UBS Axcera 334B 2000-Watt VHF Low Band Transmitter User Manual 334B

UBS-Axcera 2000-Watt VHF Low Band Transmitter 334B

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Compiled Manual 334B

INSTRUCTION MANUAL

334B

2000 WATT VHF LOW BAND

TRANSMITTER

AXCERA, LLC

103 FREEDOM DRIVE P.O. BOX 525 LAWRENCE, PA 15055-0525 USA

(724) 873-8100 • FAX (724) 873-8105

www.axcera.com • info@axcera.com

2000-Watt VHF Low Band Transmitter Table of Contents

334B, Rev. 0 i June 29, 2004

TABLE OF CONTENTS

CHAPTER 1 INTRODUCTION

SECTION PAGE

1.1 Manual Overview ............................................................................ 1-1

1.2 Assembly Designation Procedure ........................................................ 1-1

1.3 Safety........................................................................................... 1-1

1.4 Contact Information......................................................................... 1-2

1.5 Material Return Procedure................................................................. 1-2

1.6 Limited One-Year Warranty for Axcera Products .................................... 1-3

CHAPTER 2 SYSTEM DESCRIPTION, MAINTENANCE & REMOTE CONTROL

CONNECTIONS

2.1 System Overview............................................................................ 2-1

2.2 Control and Status of Transmitter....................................................... 2-4

2.2.1 VHF Exciter Tray .................................................................... 2-5

2.2.2 VHF Amplifier Tray.................................................................. 2-7

2.3 Maintenance.................................................................................. 2-8

2.4 Input Connections........................................................................... 2-9

2.5 Customer Remote Control Connections..........................................2-9

CHAPTER 3 INSTALLATION AND SETUP PROCEDURES

3.1 Site Considerations.......................................................................... 3-1

3.2 Unpacking the Cabinet and Trays ....................................................... 3-4

3.3 Installing the Cabinet and Trays......................................................... 3-5

3.4 Setup and Operation Procedures ........................................................ 3-6

CHAPTER 4 CIRCUIT DESCRIPTIONS

4.1 Low-Band VHF Exciter...................................................................... 4-1

4.1.1 Aural IF Synthesizer Board, 4.5 MHz .......................................... 4-1

4.1.2 Sync Tip Clamp/Modulator Board ............................................... 4-3

4.1.3 Delay Equalizer Board ............................................................. 4-6

4.1.4 IF Carrier Oven Oscillator Board ................................................ 4-7

4.1.4.1 IF VCXO Board .............................................................. 4-8

4.1.5 ALC Board, NTSC.................................................................... 4-9

4.1.6 IF Phase Corrector Board ........................................................4-15

4.1.7 VHF Mixer/Amplifier Enclosure Assembly ....................................4-17

4.1.7.1 x2 Multiplier Board ........................................................4-17

4.1.7.2 VHF Filter/Mixer Board ...................................................4-18

4.1.7.3 Low Band VHF Filter/Amplifier Board .................................4-18

4.1.8 Transmitter Control Board .......................................................4-19

4.1.9 Visual/Aural Metering Board.....................................................4-24

4.1.10 Channel Oscillator Assembly, Dual Oven...................................4-25

4.1.10.1 VCXO Channel Oscillator Assembly, Dual Oven ..................4-26

4.1.11 (Optional) EEPROM FSK Identifier Board...................................4-26

4.1.12 (Optional) IF Attenuator Board ...............................................4-27

4.2 VHF Low-Band Amplifier Trays..........................................................4-27

4.3 3 Way Combiner Assembly..............................................................4-31

2000-Watt VHF Low Band Transmitter Table of Contents

334B, Rev. 0 ii June 29, 2004

TABLE OF CONTENTS (continued)

SECTION PAGE

4.4 Harmonic Filter, Bandpass Filter and Coupler Assembly..........................4-31

CHAPTER 5 DETAILED ALIGNMENT PROCEDURES

5.1 VHF Low-Band Exciter Tray with Baseband Video and Audio Inputs........... 5-1

5.2 VHF Exciter Tray with 4.5-MHz Composite Input Kit ............................... 5-2

5.3 VHF Exciter Tray with Either Baseband or 4.5-MHz Composite Input.......... 5-2

5.4 IF Phase Corrector Adjustment .......................................................... 5-3

5.5 Linearity Corrector Adjustment .......................................................... 5-3

5.6 Low Band VHF Amplifier Trays ........................................................... 5-4

5.6.1 AGC Control Board.................................................................. 5-5

5.6.2 Phase Shifter Board ................................................................ 5-5

5.6.3 VHF Filter/Amplifier Board........................................................ 5-5

5.6.4 VHF Low Band Amplifier Board .................................................. 5-5

5.6.5 Overdrive Protection Board....................................................... 5-5

5.6.6 3-Way Splitter Board............................................................... 5-6

5.6.7 VHF Low Band Pallet ............................................................... 5-6

5.6.8 3-Way Combiner Board............................................................ 5-6

5.6.9 Calibration of the Visual + Aural Output Power and VSWR Cutback... 5-6

5.7 Phase and Gain Adjustment of Multiple VHF Amplifier Trays..................... 5-7

5.8 Calibration of the Forward Output Level of the Transmitter...................... 5-8

5.9 Calibration of the Reflected Output Level of the Transmitter..................... 5-8

5.10 3-Way Combiner Assembly.............................................................. 5-9

5.11 Bandpass Filter Assembly................................................................ 5-9

5.12 Complete Board Level Alignment of the VHF Exciter ............................. 5-9

5.12.1 (Optional) 4.5-MHz Composite Input Kit .................................... 5-9

5.12.2 Delay Equalizer Board............................................................ 5-9

5.12.3 Composite 4.5-MHz Filter Board..............................................5-10

5.12.4 (Optional) 4.5-MHz Bandpass Filter Board.................................5-10

5.12.5 IF Carrier Oven Oscillator Board..............................................5-10

5.12.6 Sync Tip Clamp/Modulator Board ............................................5-10

5.12.7 Aural IF Synthesizer Board, 4.5 MHz ........................................5-12

5.12.8 ALC Board (Part 1 of 2).........................................................5-13

5.12.9 IF Phase Corrector Board.......................................................5-14

5.12.10 ALC Board, NTSC (Part 2 of 2)..............................................5-14

5.12.11 Channel Oscillator Board, Dual Oven ......................................5-15

5.12.12 x2 Multiplier Board .............................................................5-15

5.12.13 VHF Filter/Mixer Board ........................................................5-16

5.12.14 VHF Low-Band Filter/Amplifier Board......................................5-16

APPENDICES

APPENDIX A SYSTEM SPECIFICATIONS

APPENDIX B SAMPLE LOG REPORT SHEET AND TYPICAL READINGS

APPENDIX C ASSEMBLY DRAWINGS AND PARTS LISTS

APPENDIX D SUBASSEMBLY DRAWINGS AND PARTS LISTS

2000-Watt VHF Low Band Transmitter Table of Contents

334B, Rev. 0 iii

LIST OF FIGURES

FIGURE PAGE

3-1 1 kW Minimum Ventilation Configuration ....................................... 3-4

3-2 Chassis Trak Cabinet Slides ........................................................ 3-5

5-1 Waveform..............................................................................5-11

2000-Watt VHF Low Band Transmitter Table of Contents

334B, Rev. 0 iv

LIST OF TABLES

TABLE PAGE

2-1 334B Trays and Assemblies ........................................................ 2-1

2-2 VHF Exciter Tray Meters............................................................. 2-5

2-3 VHF Exciter Tray Switches.......................................................... 2-6

2-4 VHF Exciter Tray Fault Indicators ................................................. 2-6

2-5 VHF Exciter Tray Samples .......................................................... 2-6

2-6 VHF Amplifier Tray Switches....................................................... 2-7

2-7 VHF Amplifier Tray Fault Indicators .............................................. 2-8

2-8 VHF Amplifier Tray Control Adjustments........................................ 2-8

2-9 VHF Amplifier Tray Sample ......................................................... 2-8

2-10 334B Customer Remote Control Connections .........................2-10

4-1 VHF Amplifier Tray Boards and Assemblies ...................................4-27

5-1 ALC Board LEDs ......................................................................5-13

2000-Watt VHF Low Band Transmitter Chapter 1, Introduction

334B, Rev. 0 1-1

Chapter 1

Introduction

This manual explains the installation,

setup, alignment, and maintenance

procedures for the 334B 2000-watt solid

state VHF Low Band transmitter. It is

important that you read all of the

instructions, especially the safety

information in this chapter, before you

begin to install or operate the unit.

1.1 Manual Overview

This instruction manual is divided into

five chapters and supporting appendices.

Chapter 1, Introduction, contains

information on the assembly numbering

system used by Axcera, safety, contact

information, return procedures, and

warranties. Chapter 2, System

Description, Maintenance and Remote

Control Connections, describes the

transmitter and includes discussions on

system control and status indicators,

maintenance and remote control

connections. Chapter 3 Installation and

Set Up Procedure, explains how to

unpack, install, setup, and operate the

transmitter. Chapter 4, Circuit

Descriptions, contains a detailed

discussion of the circuits and boards that

make up the 334B. Chapter 5, Detailed

Alignment Procedures, provides

information on adjusting the system and

trays to achieve peak operation of the

transmitter and assemblies. The

appendices contain system

specifications, a sample log sheet, typical

operational readings, interconnects,

schematics, assembly and subassembly

drawings and parts lists.

1.2 Assembly Designation Procedure

Axcera has assigned assembly numbers,

such as Ax (x=1,2,3…), to all assemblies,

trays, subassemblies, and boards that

make up the 334B. The assembly

numbers are referenced to in the text of

this manual and shown on the block

diagrams and interconnect drawings

provided in the appendices. These

supporting documents are arranged in

increasing numerical order in the

appendices. Section titles in the text for

assembly, tray descriptions and

alignment procedures also indicate the

associated drawing(s) and the relevant

appendix that contains the drawing.

Sections describing vendor-supplied

items, such as meters and power

supplies, do not contain this information.

1.3 Safety

The transmitters manufactured by Axcera

are designed for ease of operation and

repair while providing protection from

electrical and mechanical hazards. Listed

throughout the manual are notes,

cautions, and warnings concerning

possible safety hazards that may be

encountered while operating or servicing

the transmitter. Please review these

warnings and familiarize yourself with the

operation and servicing procedures

before attempting to maintain or repair

the transmitter.

Read All Instructions – All of the

operating and safety instructions should

be read and understood before operating

this equipment.

Retain Manuals – An instruction manual

provided with the transmitter should be

retained at the transmitter site for future

reference. Axcera provides two

instruction manuals for this purpose; one

manual can be left at the office while the

other can be kept at the site.

Heed all Notes, Warnings, and

Cautions – The avoid injury or damage

to the equipment, all of the notes,

warnings, and cautions listed in this

safety section and throughout the

manual must be followed.

2000-Watt VHF Low Band Transmitter Chapter 1, Introduction

334B, Rev. 0 1-2

Follow Instructions – All of the

operating and use instructions for the

transmitter should be followed.

Cleaning – Unplug or otherwise

disconnect all power from the equipment

before cleaning. Do not use liquid or

aerosol cleaners as damage to silk

screens may occur. Use a damp cloth for

cleaning.

Ventilation – Openings in the cabinets

and tray front panels are provided for

ventilation. To ensure reliable operation

of the transmitter, and to protect the unit

from overheating, these openings must

not be blocked and cleaned regularly.

Servicing – Do not attempt to service

this product yourself until becoming

familiar with the equipment. If in doubt,

refer all servicing questions to qualified

Axcera service personnel.

Replacement Parts – When

replacement parts are needed, use the

replacement part numbers as given on

the parts lists included in this manual, in

Appendix C or Appendix D. If other parts

are used, be sure that the parts have the

same functional and performance

characteristics as the original part.

Unauthorized substitutions may result in

fire, electric shock, or other hazards.

Please contact the Axcera field service

department if you have any questions

regarding service or replacement parts.

1.4 Contact Information

The Axcera Field Service Department can

be contacted by phone at (724) 873-

8100 or by fax at (724) 873-8105.

Before calling Axcera, please be prepared

to supply the Axcera technician with

answers to the following questions. This

will save time and help ensure the most

direct resolution to the problem.

1. What are the Customers’ Name and

call letters?

2. What are the model number and

type of transmitter?

3. Is the transmitter digital or analog?

4. How long has the transmitter been

on the air? (Approximately when

was the transmitter installed.)

5. What are the symptoms being

exhibited by the transmitter?

Include the status as read on the

LCD display, if present. Also record

the status of any LEDs located on

the front panels of the Trays.

Include all meter readings from the

trays.

1.5 Material Return Procedure

To insure the efficient handling of

equipment or components that have been

returned for repair, Axcera requests that

each returned item be accompanied by a

Material Return Authorization Number

(MRA#).

An MRA# can be obtained from any

Axcera Field Service Engineer by

contacting the Axcera Field Service

Department at (724) 873-8100 or by fax

at (724) 873-8105. This procedure

applies to all items sent to the Field

Service Department regardless of

whether the item was originally

manufactured by Axcera.

NOTE: To prevent damage to the product

during shipping, Axcera will supply a

shipping container to the customer upon

request.

When equipment is sent to the field on

loan, an MRA# is included with the unit.

The MRA# is intended to be used when

the unit is returned to Axcera. All

shipping material should be retained for

the return of the unit to Axcera.

Replacement assemblies are also sent

with an MRA# to allow for the proper

routing of the exchanged hardware.

Failure to close out this type of MRA# will

normally result in the customer being

invoiced for the value of the loaner item

or the exchange assembly.

2000-Watt VHF Low Band Transmitter Chapter 1, Introduction

334B, Rev. 0 1-3

When shipping an item to Axcera, please

include the MRA# on the packing list and

on the shipping container. The packing

list should also include contact

information and a brief description of why

the unit is being returned.

Please forward all MRA items to:

Axcera, LLC

103 Freedom Drive

P.O. Box 525

Lawrence, PA 15055-0525 USA

For more information concerning this

procedure, call the Axcera Field Service

Department.

Axcera can also be contacted through

e-mail at info@axcera.com and on the

Web at www.axcera.com.

1.6 Limited One-Year Warranty for

Axcera Products

Axcera warrants each new product that

it has manufactured and sold against

defects in material and workmanship

under normal use and service for a

period of one (1) year from the date of

shipment from Axcera's plant, when

operated in accordance with Axcera's

operating instructions. This warranty

shall not apply to tubes, fuses,

batteries, or bulbs.

Warranties are valid only when and if

(a) Axcera receives prompt written

notice of breach within the period of

warranty, (b) the defective product is

properly packed and returned by the

buyer (transportation and insurance

prepaid), and (c) Axcera determines, in

its sole judgment, that the product is

defective and not subject to any misuse,

neglect, improper installation,

negligence, accident, or (unless

authorized in writing by Axcera) repair

or alteration. Axcera's exclusive liability

for any personal and/or property

damage (including direct, consequential,

or incidental) caused by the breach of

any or all warranties, shall be limited to

the following: (a) repairing or replacing

(in Axcera's sole discretion) any

defective parts free of charge (F.O.B.

Axcera’s plant) and/or (b) crediting (in

Axcera's sole discretion) all or a portion

of the purchase price to the buyer.

Equipment furnished by Axcera, but not

bearing its trade name, shall bear no

warranties other than the special hours-

of-use or other warranties extended by

or enforceable against the manufacturer

at the time of delivery to the buyer.

NO WARRANTIES, WHETHER

STATUTORY, EXPRESSED, OR

IMPLIED, AND NO WARRANTIES OF

MERCHANTABILITY, FITNESS FOR

ANY PARTICULAR PURPOSE, OR

FREEDOM FROM INFRINGEMENT,

OR THE LIKE, OTHER THAN AS

SPECIFIED IN PATENT LIABILITY

ARTICLES, AND IN THIS ARTICLE,

SHALL APPLY TO THE EQUIPMENT

FURNISHED HEREUNDER.

2000-Watt VHF Low Band Transmitter Chapter 2, System Description,

Maintenance & Remote Control Connections

334B, Rev. 0 2-1

Chapter 2

System Description, Maintenance & Remote Control Connections

The 334B is a complete 2000-watt VHF

Low Band solid state internally diplexed

television transmitter that operates at a

nominal visual output power of 2000

watts peak sync and an average aural

output power of 200 watts, at an A/V

ratio of 10 dB, 10% sound, or 100 watts

at 13 dB, 5% sound.

2.1 System Overview

The 334B (1304407) is made up of the

trays and assemblies listed in Table 2-1.

Table 2-1. 334B Trays and Assemblies

MAJOR ASSEMBLY

DESIGNATOR TRAY/ASSEMBLY NAME DRAWING NUMBER

A2 AC distribution block

A4 VHF L.B. exciter 1070820 or

1304463 w/Precise Frequency

A6, A7 & A11 Three VHF amplifier trays 1304363

A8 VHF combiner assembly 1065241

A13 Harmonic filter 1304390

A14 Bandpass filter assembly 1304388

A12 Remote interface assembly 1083510

(Optional)

A25 Precise Frequency Control Tray 1294-1153(+), 1294-1154(0)

or 1294-1155(-)

VHF L.B. Exciter Tray

The (A4) VHF L.B. exciter tray (1070820)

operates using baseband audio and video

inputs to produce a diplexed, modulated,

and on-channel frequency visual + aural

RF output.

NOTE: If your transmitter contains a

precise frequency kit, a precise frequency

control tray provides the PLL circuits that

connect to the VHF exciter tray w/precise

frequency (1304463) for precise channel

oscillator frequency control. Refer to the

334B precise frequency control system

instruction manual for information on the

precise frequency control tray and

system.

Aural IF Synthesizer Board

The baseband audio, either balanced at

TB1 or composite at J6, and the

subcarrier audio at J4, if present, connect

from the rear of the VHF exciter to (A4)

the aural IF synthesizer board (1265-

1303). The board amplifies and controls

the levels of the three possible audio

inputs and provides a single audio

output. A 4.5-MHz CW signal is

generated using a voltage controlled

oscillator (VCO), onto which the audio is

modulated. This produces the modulated

4.5 MHz output of the board that

connects to the sync tip modulator board.

The board also contains a phase lock loop

(PLL) circuit that maintains the precise

4.5-MHz separation between the aural

(41.25 MHz) and the visual (45.75 MHz)

IF frequencies

Sync Tip Clamp/Modulator Board

The baseband video connects from J1 on

the rear of the VHF exciter to (A5) the

sync tip clamp/modulator board (1265-

1302). The sync tip clamp/modulator

board takes the video, amplifies it,

provides a sync tip clamp circuit and

modulates the video with a 45.75 MHz IF

generated by the IF carrier oven

oscillator or IF VCXO board. The audio

2000-Watt VHF Low Band Transmitter Chapter 2, System Description,

Maintenance & Remote Control Connections

334B, Rev. 0 2-2

modulated 4.5 MHz IF, from the aural IF

synthesizer board, is mixed with the

45.75 MHz CW to produce a modulated

41.25 MHz aural IF output. The video

modulated 45.75 MHz is then diplexed

with the audio modulated 41.25 MHz to

produce the combined Visual IF + Aural

IF output of the board that connects to

the ALC board.

4.5 MHz Composite Input Kit

NOTE: If your transmitter does not

contain the 4.5 MHz composite input kit,

the following paragraph description does

not pertain. If the (optional) 4.5-MHz

composite input kit is purchased, the 4.5-

MHz composite input or the baseband

video and audio inputs are used. The

switching between the inputs is

accomplished by a relay mounted on the

sync tip clamp modulator board that is

controlled by a baseband select. The

baseband select controls a relay that

selects either the 4.5 MHz generated

from the baseband inputs or from the

4.5-MHz composite input. To operate the

transmitter with the (optional) 4.5-MHz

composite input kit using baseband

inputs, the baseband video must be

connected to J1 or J2, the baseband

audio must be connected to the proper

input jack, and a baseband select must

be connected from J7-6 and J7-7. To

operate the transmitter with the

(optional) 4.5-MHz composite input kit

using the 4.5-MHz composite input, the

4.5-MHz composite input must be

connected to J1 or J2 and the baseband

select must be removed from J7-6 and

J7-7.

IF Carrier Oven Oscillator Board

NOTE: If the precise frequency kit is

present in your transmitter, the IF VCXO

Board (1248-1131) will be used.

The IF carrier oven oscillator (1191-

1404) or the IF VCXO board generates

the 45.75 MHz visual IF CW signal that

connects to the sync tip clamp/modulator

board.

ALC Board

The (A8) automatic level control (ALC)

board (1265-1305) provides the ALC and

amplitude linearity correction of the

45.75 MHz + 41.25 MHz IF signal. The

ALC circuit adjusts the level of the

combined IF signal through the board

that controls the output power of the

transmitter. The level controlled

combined IF output of the ALC board

connects to the filter/mixer board.

VHF L.B. Filter/Mixer Board

The (A11-A2) VHF filter/mixer board

(1153-1101) is made up of three

separate circuits. The on channel

frequency RF output of the x2 multiplier

board connects to a filter and amplifier

circuit before it is connected to the mixer

stage. The combined 41.25 MHz + 45.75

MHz IF from the ALC board also connects

to the mixer stage. The RF output of the

mixer is filtered and amplified in the final

circuit before it is connected to the VHF

filter amplifier board.

X2 Multiplier Board

The (A11-A1) x2 multiplier board (1172-

1111) multiplies the frequency of the RF

from the channel oscillator by a factor of

two using a broadband frequency doubler

circuit. The RF on channel frequency

output of the board connects to the

filter/mixer board.

VHF Low Band Filter Amplifier Board

The VHF low band filter/amplifier board

(1064251) is made up of two separate

circuits. The RF output of the filter/mixer

board is connected to a filter circuit tuned

for best response on the channel

frequency. The filtered RF is then

connected to an amplifier circuit with a

manual gain control. The output of the

board connects to J15, the RF output jack

located on the rear of the VHF exciter

tray

2000-Watt VHF Low Band Transmitter Chapter 2, System Description,

Maintenance & Remote Control Connections

334B, Rev. 0 2-3

Channel Oscillator Board

NOTE: If the precise frequency kit is

present in your transmitter, the VCXO

Channel Oscillator Board (1145-1204)

will be used.

The channel oscillator board (1145-1201)

or VCXO board generates a stable

frequency reference signal of

approximately 100 MHz. The output

connects to the x2 multiplier board.

Transmitter Control Board

The (A17) transmitter control board

(1265-1311) provides system control

functions and the operational LED

indications, which can be viewed on the

front panel of the transmitter. The main

control functions are the

Operate/Standby and Auto/Manual

selections. When the transmitter is

switched to Operate, the board supplies

the enables to the three external VHF

amplifier trays. The board also performs

the automatic switching of the

transmitter to Standby upon the loss of

the video input when the transmitter is in

Automatic.

Visual/Aural Metering Board

The (A19) visual/aural metering board

(1265-1309) provides detected outputs

of the visual, aural, and reflected output

samples that are used for monitoring on

the front panel meter. These readings are

attained from the forward power and the

reflected power samples from the output

coupler assembly of the transmitter.

4 Way Power Splitter

The RF output of the VHF exciter is split

four ways in (A5) the 4-way power

splitter assembly (ZFSC-4-3BNC). Only

three of the outputs are used in this

configuration, the fourth is terminated.

VHF Low Band Amplifier Tray

The outputs of the splitter feed the three

(A6, A7 and A11) VHF amplifier trays

(1304363). Each tray amplifies the RF

signals to approximately 750 watts peak

of sync visual + aural.

In the VHF amplifier tray, a forward

power sample and a reflected power

sample from the combiner board are

connected to the AGC control board that

provides peak-detected samples that are

monitored on the front panel meter of

the tray.

3 Way VHF Combiner Assembly

The outputs of the three VHF amplifier

trays are combined in (A8) the 3 way

VHF combiner that provides

approximately 2100 watts peak of sync

output.

Harmonic and Bandpass Filters

The output of the combiner assembly is

connected to (A13) a harmonic filter and

(A14) a bandpass filter assembly. The

harmonic and bandpass filters are tuned

to provide a high out-of-band rejection of

unwanted products.

Output Coupler Assembly

The filtered signal is connected to the

(A16) coupler assembly, which provides

a forward and a reflected power sample

to the visual/aural metering board

mounted in the VHF exciter. The forward

sample is processed to provide peak

detected visual and aural power output

samples to the transmitter control board

in the VHF exciter. The reflected power

sample is also peak detected and wired

to the transmitter control board. The

transmitter control board connects the

visual, aural, and reflected power output

samples to the front panel meter for

visual monitoring of the system

operation.

2000-Watt VHF Low Band Transmitter Chapter 2, System Description,

Maintenance & Remote Control Connections

334B, Rev. 0 2-4

2.2 Control and Status of Transmitter

Control and status information for the

transmitter is provided by the meter and

LED indicators on the front panel of the

VHF exciter. The switches and LED

indicators are part of the (A17)

transmitter control board that is mounted

so that the switches and LEDs are

operated or viewed from the front panel

of the VHF exciter.

Switch S1 is an Operate/Standby switch

that controls the output of the

transmitter by providing the Enables

that, when the transmitter is in Operate,

are needed to turn on the switching

power supplies in the three VHF amplifier

trays. When the transmitter is in

Operate, the green LED DS2, located on

the front panel of the VHF exciter. When

it is in Standby, the amber LED DS1 is

on. If the transmitter does not switch to

Operate when S1 is switched to Operate,

check that a dummy jumper plug is

connected to (A12-J9 at pins 21 and 22)

on the remote interface panel. It must

be present for the transmitter to operate.

If the interlock is present, the green LED

DS5, mounted on the transmitter control

board, will be lit.

NOTE: If the remote interface panel is

not present in your transmitter the

dummy jumper plug must be present on

J11, with a jumper between pins 23 and

24, located on the back of the VHF

exciter tray. The jumper provides the

interlock needed for the transmitter to

operate. If the interlock is present, the

green LED DS5, mounted on the

transmitter control board, will be lit.

Switch S2 is an Automatic/Manual switch

that controls the operation of the

transmitter by the presence of the video

input signal. When the switch is in

Automatic, the green LED DS3 is lit and,

if the video input signal to the

transmitter is lost, the transmitter will

automatically switch to Standby. When

the video input signal returns, the

transmitter will automatically switch back

to Operate. In Manual, the amber LED

DS4 is lit and the operation of the

transmitter is controlled by the front

panel switches. During normal operation

of the transmitter, switch S2 should be in

the Auto position. The front panel of the

VHF exciter also has LEDs that indicate a

Video Fault (red LED DS9) and VSWR

Cutback (amber LED DS7).

2000-Watt VHF Low Band Transmitter Chapter 2, System Description,

Maintenance & Remote Control Connections

334B, Rev. 0 2-5

2.2.1 VHF Exciter Tray (A4)

Table 2-2. VHF Exciter Tray Meters

METER FUNCTION

This meter reads power in terms of a percentage of the calibrated

output power level on the upper scale. The voltage level or

frequency level is read on one of the bottom two scales. A full-

scale reading on the top scale is 120%. 100% is equivalent to the

full-rated 2000 watts peak of sync visual. The meter also reads %

Aural Power, % Exciter Power, % Reflected Power, audio levels,

video levels, and the ALC reading.

With Switch S3 in Position Display

Switch S3, Meter

Selects the desired ALC voltage

reading, % Exciter Power,

% Reflected Power, % Visual

Power, % Aural Power, video

level, or audio level.

Audio

(0 to 100 kHz)

Reads the audio level, ±25 kHz

balanced or ±75 kH composite,

on the 0 to 10 scale. Will indicate

baseband audio, if it is connected

to the transmitter, even with the

(optional) video + 4.5-MHz SCA

input selected.

ALC

(0 to 10 volts) Reads the ALC voltage level,

.8 VDC, on the 0 to 10 scale.

% Exciter

(0 to 120)

Reads the % Exciter Output

Power Level needed to attain

100% output of the transmitter

on the top scale.

% Aural Power

(0 to 120)

Reads the % Aural Output Power

of the transmitter,

100% = 200 watts at 10 dB A/V

ratio, on the top scale.

% Visual Power

(0 to 120)

Reads the % Visual Output Power

of the transmitter,

100% = 2000 watts peak of sync,

on the top scale.

% Reflected

(0 to 120) Reads the % Reflected Output

Power, <5%, on the top scale.

Meter (A4-A18)

Video

(0 to 1 volt) Reads the video level, at white,

on the bottom 0 to 10 scale.

2000-Watt VHF Low Band Transmitter Chapter 2, System Description,

Maintenance & Remote Control Connections

334B, Rev. 0 2-6

Table 2-3. VHF Exciter Tray Switches

SWITCH FUNCTION

Transmitter

Operate/Standby

The momentary switch S1 applies a ground to K1, a latching

relay on the transmitter control board. K1 will switch either

to Operate or to Standby depending on which direction S1 is

pushed. When switched to Operate, the low, Enable

commands are applied to the VHF amplifier trays. These

Enables will turn on the VHF amplifier trays. The opposite

occurs when the switch is turned to Standby.

Mode Select

Auto/Manual

The momentary switch S2 applies a ground to K2, a latching

relay on the transmitter control board. K2 will switch the

transmitter to Automatic or Manual depending on which

direction S2 is pushed. In Automatic, the video fault

command from the ALC Board will control the operation of

the transmitter. The transmitter will switch to Standby, after

a slight delay, if the input video is lost and will switch back to

Operate, quickly, when the video is restored. In Manual, the

transmitter is controlled by the operator using the front panel

Operate/Standby switch or by remote control.

Power Adjust The 5 kΩ pot (A20) sets the ALC level on the ALC board that

controls the output power of the transmitter.

Table 2-4. VHF Exciter Tray Fault Indicators

INDICATOR DESCRIPTION

DS9

Video Loss

(Red)

Indicates that the input video to the transmitter has been

lost. The fault is generated on the ALC board in the VHF

exciter tray.

DS7

VSWR Cutback

(Amber)

Indicates that the reflected power level of the transmitter has

increased above 20%. This automatically cuts back the

output power level to 20%. The fault is generated on the

transmitter control board in the VHF exciter tray.

Table 2-5. VHF Exciter Tray Samples

SAMPLE DESCRIPTION

f(IF) A sample of the visual IF that is taken from the sample jack

on the IF carrier oven oscillator board.

f(IC) A sample of the intercarrier signal that is taken from the

sample jack on the aural IF synthesizer board.

f(s) A sample of the channel oscillator output that is taken from

the sample jack of the channel oscillator assembly.

Exciter O/P An output power sample of the exciter that is taken from the

VHF filter/amplifier board.

Transmitter O/P A forward power sample of the transmitter that is taken from

the output coupler assembly through the visual/aural

metering board.

2000-Watt VHF Low Band Transmitter Chapter 2, System Description,

Maintenance & Remote Control Connections

334B, Rev. 0 2-7

2.2.2 VHF Amplifier Tray (A6, A7 & A11)

Table 2-6. VHF Amplifier Tray Switches

SWITCH FUNCTION

CB1

On/Off Circuit Breaker

Switches 220 VAC through a 15-amp circuit breaker-type

protection device. The switch lights if AC is present. The

AC is applied to the switching power supply in the tray.

Selects the desired % Visual Forward Output Power, %

Visual Reflected Power reading, AGC Voltage, Power Supply

Voltage, or Current

With Switch S1 in

Position Display

% Forward Reads the % Forward Output

Power of the tray (100%= 750

watts peak of sync + aural)

% Refl (Reflected) Reads the % Reflected Output

Power (<5%)

AGC Voltage Reads the AGC level of the tray

(1 to 3 VDC)

Power Supply Reads the voltage from the

switching power supply

(+30 VDC)

Switch, Meter

Current Uses Switch S2 to indicate the

current of transistor devices

Selects the current of the transistor devices on the high

band amplifier boards. S1 must be in the Current position.

With Switch S2 in

Position Display

Reads the current of (A3-A1) the

low band amplifier board (idling

current=1.8 amps and operating

current=12-13 amps, black

picture)

Reads the current of (A3-A2) the

low band amplifier board (idling

current=1.8 amps and operating

current=12-13 amps, black

picture)

Reads the current of (A3-A3)

the low band amplifier board

(idling current=1.8 amps and

operating current=12-13 amps,

black picture)

Switch, Meter

Reads the current of (A2-A1) the

low band amplifier board (idling

current=3 amps and operating

current=3 amps, black picture)

2000-Watt VHF Low Band Transmitter Chapter 2, System Description,

Maintenance & Remote Control Connections

334B, Rev. 0 2-8

Table 2-7. VHF Amplifier Tray Fault Indicators

INDICATOR DESCRIPTION

DS1

Overdrive

Indicates that the level of drive is too high. The protection

circuit will limit the drive level to the set threshold. The fault

is generated on the overdrive protection board.

DS2

Enable Indicates that the Enable supplied by the exciter tray is

present

DS3

Module Status Indicates that the forward power sample level is lower than

the set reference level

DS4

VSWR Cutback

Indicates that the reflected level of the tray has increased

above 20%; this will automatically cut back the output power

of the tray. The fault is generated on the AGC control board.

DS5

Overtemperature

Indicates that the temperature of (A4-A5, A4-A6 or A5-A2)

one of the thermal switches is above 175° F. When this fault

occurs, the Enable to the switching power supply is

immediately removed.

Table 2-8. VHF Amplifier Tray Control Adjustments

ADJUSTMENT DESCRIPTION

R2 – A7

Phase Adjusts the phase of the RF output by approximately 70°.

R3 – A6

Gain Adjusts the gain of the RF output when the amplifier control

board is in the AGC mode.

Table 2-9. VHF Amplifier Tray Sample

SAMPLE DESCRIPTION

RF Front Panel Sample Forward power sample of the tray from the AGC control

board.

2.3 Maintenance

The 334B is designed with components

that require little or no periodic

maintenance except for the routine

cleaning of the fans and the openings in

front panels of the trays.

The amount of time between cleanings

depends on the conditions within the

transmitter room. While the electronics

have been designed to function even if

covered with dust, a heavy buildup of

dust, dirt, or insects will affect the

cooling of the components. This could

lead to a thermal shutdown or premature

failure of the affected trays.

When the front panels of the trays

become dust covered, the top covers

should be removed and any accumulated

foreign material should be removed. A

vacuum cleaner, utilizing a small wand-

type attachment, is an excellent way to

suction out the dirt. Alcohol and other

cleaning agents should not be used

unless you are certain that the solvents

will not damage components or the silk-

screened markings on the trays and

boards. Water-based cleaners can be

used, but do not saturate the

components. The fans and heatsinks

should be cleaned of all dust or dirt to

permit the free flow of air for cooling

purposes.

It is recommended that the operating

parameters of the transmitter be

recorded from the meters on the trays at

least once a month. It is suggested that

2000-Watt VHF Low Band Transmitter Chapter 2, System Description,

Maintenance & Remote Control Connections

334B, Rev. 0 2-9

this data be retained in a rugged folder

or envelope. A sample format for a log

sheet is provided in Appendix B.

Photocopies of the log sheet should be

made to allow you to make continued

data entries.

2.4 Input Connections

The baseband audio input connects to

(A12) the A/V input and remote interface

assembly. The baseband audio connects

to TB1 for balanced audio or to jack J6

for composite, stereo, audio. The

baseband video input connects to jack

J2. NOTE: If another transmitter is

using the same composite audio and

video inputs, the loop through

connections on the rear of the VHF

exciter can be used. The video can be

connected to J2 and the composite audio

to J13.

NOTE: If your transmitter contains a

precise frequency kit, a 5/10 MHz

reference input must be connected to the

BNC jack J19 on the remote interface

assembly.

NOTE: If your transmitter contains a

receiver tray the RF input connects to the

“N” connector J1 or the “F” connector J18

on the remote interface assembly.

If the (A12) A/V input and remote

interface panel is not present in your

system, the baseband video and audio

inputs connect directly to the rear of the

VHF exciter.

NOTE: If your transmitter does not

contain the 4.5 MHz composite input kit,

the following description does not pertain

to your transmitter. The baseband video

input or the 4.5-MHz composite input

connects to jacks J1 or J2, which are

loop-through connected. The baseband

audio input connects to TB1 for balanced

audio or to jacks J3 or J13, which are

loop-thru connected, for composite,

stereo, audio. To use the (Optional) 4.5-

MHz composite input kit, the baseband

audio can remain connected to the VHF

exciter even if the 4.5-MHz composite

input kit is used, but the baseband video

must be removed from J1 or J2 and the

4.5-MHz composite input must be

connected to J1 or J2. The baseband

select command must be removed from

J7-6 and J7-7.

2.5 Remote Connections

The remote connections listed in Table 2-

10 are made to the (A12) A/V input and

remote interface assembly. The remote

connections are made to the 37 pos “D”

connector J9 or the 25 pos “D” connector

J10 on the assembly. Refer to the

interconnect drawing (1304391) to

confirm the remote pin connections.

2000-Watt VHF Low Band Transmitter Chapter 2, System Description,

Maintenance & Remote Control Connections

334B, Rev. 0 2-10

Table 2-10. 334B Remote Interface Connections to (A12) the A/V Input

and Remote Interface Assembly

FUNCTION REMOTE JACK/PIN

NUMBER INTERFACE TYPE

Transmitter Enable Interlock J9-21

Transmitter Enable Interlock Rtn. J9-22

J9-21 and J9-22 must be

connected together for

normal operation. The

(1176-1038) jumper jack or

an external interlock can be

used.

Remote Control Commands

Transmitter Standby (Disable) J9-9 Contact closure

Transmitter Standby/Operate Rtn. J9-10

Transmitter Operate (Enable) J9-11 Contact closure

Transmitter Manual J9-15 Contact closure

Transmitter Auto/Manual Rtn. J9-16

Transmitter Auto J9-17 Contact closure

Power Level Raise (Optional) J9-27 Contact closure

Pwr Lvl Raise/Lower Rtn (Optional) J9-28

Power Level Lower (Optional) J9-29 Contact closure

Modulator Select (Optional) J9-31 Contact closure

Modulator Select Rtn (Optional) J9-32

Remote Status Indications

Transmitter Operate (Enable) Ind. J9-12 50 mA max current sink

Operate/Standby Ind. Return J9-13

Transmitter Standby (Disable) Ind. J9-14 50 mA max current sink

Transmitter Auto Indicator J9-18 50 mA max current sink

Auto/Manual Indicator Return J9-19

Transmitter Manual Indicator J9-20 50 mA max current sink

VSWR Cutback Indicator J9-23 50 mA max current sink

VSWR Cutback Indicator Return J9-24

Video Loss (Fault) Indicator J9-25 50 mA max current sink

Video Loss (Fault) Ind. Rtn. J9-26

Receiver Fault (Optional) J9-30

2000-Watt VHF Low Band Transmitter Chapter 2, System Description,

Maintenance & Remote Control Connections

334B, Rev. 0 2-11

FUNCTION REMOTE JACK/PIN

NUMBER INTERFACE TYPE

Remote Metering

Visual Output Power J9-1

Visual Output Power Rtn J9-2 1V full scale at 1kΩ source

resistance

Aural Output Power J9-3

Aural Output Power Rtn J9-4 1V full scale at 1kΩ source

resistance

Reflected Power J9-5

Reflected Power Rtn J9-6 1V full scale at 1kΩ source

resistance

Exciter Output Power J9-7

Exciter Output Power Rtn J9-8 1V full scale at 1kΩ source

resistance

Forward Output Power (A6) VHF

Amp #1 J10-1

Forward Output Power (A6) Rtn J10-2

1V full scale at 1kΩ source

resistance

Reflected O/P Power (A6) VHF

Amp #1 J10-3

Reflected O/P Power (A6) Rtn J10-4

1V full scale at 1kΩ source

resistance

Forward Output Power (A7) VHF

Amp #2 J10-6

Forward Output Power (A7) Rtn J10-7

1V full scale at 1kΩ source

resistance

Reflected O/P Power (A7) VHF

Amp #2 J10-8

Reflected O/P Power (A7) Rtn J10-9

1V full scale at 1kΩ source

resistance

Forward Output Power (A11) VHF

Amp #3 J10-10

Forward Output Power (A11 Rtn J10-11

1V full scale at 1kΩ source

resistance

Reflected O/P Power (A11 VHF

Amp #3 J10-12

Reflected O/P Power (A11) Rtn J10-13

1V full scale at 1kΩ source

resistance

NOTE: If your transmitter does not

contain the (A12) A/V input and remote

interface assembly, the remote

connections are made directly to the rear

of the VHF exciter at J10 a 25 pos “D”

connector or J11 a 37 pos “D” connector

and to each of the VHF amplifier trays at

J3 a 25 pos “D” connector. Refer to the

interconnect drawing (1304391) to

confirm the remote pin connections.

This concludes this chapter on the

System Description, Maintenance and

Remote Control Connections.

2000-Watt VHF Low Band Transmitter Chapter 3, Installation and Setup Procedures

334B, Rev. 0 3-1

Chapter 3

Installation and Setup Procedures

There are special considerations that

need to be taken into account before the

334B can be installed. For example, if

the installation is completed during cool

weather, a heat-related problem may not

surface for many months, suddenly

appearing during the heat of summer.

This section provides planning

information for the installation and set up

of the transmitter.

3.1 Site Considerations

The transmitter requires an AC input line

of 220 VAC with a rating of 25 amps that

connects to the transmitter cabinet.

Make sure that the proposed site for the

transmitter has the necessary voltage

requirements.

The 334B is designed and built to provide

long life with a minimum of maintenance.

The environment in which it is placed is

important and certain precautions must

be taken. The three greatest dangers to

the transmitter are heat, dirt, and

moisture. Heat is usually the greatest

problem, followed by dirt, and then

moisture. Over-temperature can cause

heat-related problems such as thermal

runaway and component failure. Each

amplifier tray in the transmitter contains

a thermal interlock protection circuit that

will shut down that tray until the

temperature drops to an acceptable level.

A suitable environment for the

transmitter can enhance the overall

performance and reliability of the

transmitter and maximize revenues by

minimizing down time. A properly

designed facility will have an adequate

supply of cool, clean air, free of airborne

particulates of any kind, and no

excessive humidity. An ideal

environment will require temperature in

the range of 40° F to 70° F throughout

the year, reasonably low humidity, and a

dust-free room. It should be noted that

this is rarely if ever attainable in the real

world. However, the closer the

environment is to this design, the greater

the operating capacity of the transmitter.

The fans, designed and built into the

transmitter, will remove the heat from

within the trays, but additional means

are required for removing this heat from

the building. To achieve this, a few

issues need to be resolved. The first step

is to determine the amount of heat to be

removed from the transmitter room.

There are generally three sources of heat

that must be considered. The first and

most obvious is the heat from the

transmitter itself. This can be

determined by subtracting the average

power to the antenna (1400 watts) from

the AC input power (4800 watts) . This

number in watts (3400) is then multiplied

by 3.41, which gives 11,594, the BTUs to

be removed every hour. 12,000 BTUs

per hour equals one ton, so a 1-ton air

conditioner will cool a 2000-watt

transmitter.

The second source of heat is other

equipment in the same room. This

number is calculated in the same way as

the equation for BTUs. The third source

of heat is equally obvious but not as

simple to calculate. This is the heat

coming through the walls, roof, and

windows on a hot summer day. Unless

the underside is exposed, the floor is

usually not a problem. Determining this

number is usually best left up to a

qualified HVAC technician. There are far

too many variables to even estimate this

number without reviewing the detailed

drawings of the site that show all of the

construction details. The sum of these

three sources is the bulk of the heat that

must be removed. There may be other

sources of heat, such as personnel, and

all should be taken into account.

2000-Watt VHF Low Band Transmitter Chapter 3, Installation and Setup Procedures

334B, Rev. 0 3-2

Now that the amount of heat that must

be removed is known, the next step is to

determine how to accomplish this. The

options are air conditioning, ventilation,

or a combination of the two. Air

conditioning is always the preferred

method and is the only way to create

anything close to an ideal environment.

Ventilation will work quite well if the

ambient air temperature is below 100° F,

or about 38° C, and the humidity is kept

at a reasonable level. In addition, the air

stream must be adequately filtered to

ensure that no airborne particulates of

any kind will be carried into the

transmitter. The combination of air

conditioning for summer and ventilation

during the cooler months is acceptable,

when the proper cooling cannot be

obtained through the use of ventilation

alone and using air conditioning

throughout the year is not feasible.

Caution: The use of air conditioning

and ventilation simultaneously is not

recommended. This can cause

condensation in transmitters.

The following precautions should be

observed regarding air conditioning

systems:

1. Air conditioners have an ARI

nominal cooling capacity rating.

In selecting an air conditioner, do

not assume that this number can

be equated to the requirements of

the site. Make certain that the

contractor uses the actual

conditions that are to be

maintained at the site in

determining the size of the air

conditioning unit. With the

desired conditioned room

temperature under 80° F, the unit

must be derated, possibly by a

substantial amount.

2. Do not have the air conditioner

blowing directly onto the

transmitter. Condensation may

occur on, or worse in, the

transmitter under certain

conditions.

3. Do not isolate the front of the

transmitter from the back with the

thought of air conditioning only

the front of the unit. Cooling air is

drawn in at the front of all

transmitters and in the front and

back of others. Any attempt to

isolate the front from the rear will

adversely affect the flow of cooling

air.

4. Interlocking the transmitter with

the air conditioner is

recommended to keep the

transmitter from operating without

the necessary cooling.

5. The periodic cleaning of all filters

is a must.

When using ventilation alone, the

following general statements apply:

1. The blower, with attendant filters,

should be on the inlet, thereby

pressurizing the room and

preventing dirt from entering the

transmitter.

2. The inlet and outlet vents should

be on the same side of the

building, preferably the leeward

side. As a result, the pressure

differential created by wind will be

minimized. Only the outlet vent

may be released through the roof.

3. The inlet and outlet vents should

be screened with 1/8-inch

hardware cloth (preferred) or

galvanized hardware cloth

(acceptable).

4. Cooling air should enter the room

as low as practical but in no case

higher than four feet above the

floor. The inlet must be located

where dirt, leaves, snow, etc., will

not be carried in with the cooling

air.

2000-Watt VHF Low Band Transmitter Chapter 3, Installation and Setup Procedures

334B, Rev. 0 3-3

5. The exhaust should be located as

high as possible. Some ducting is

usually required to insure the

complete flushing of heated air

with no stagnant areas.

6. The area of the filter, located in

the ducting, must be large enough

to insure a maximum air velocity

of 300 feet per minute through the

filter. This is not a conservative

number but a never-exceed

number. In a dusty or remote

location, this number should be

reduced to 150 CFM.

7. The inlet and outlet(s) must have

automatic dampers that close any

time the ventilation blower is off.

8. In those cases in which

transmitters are regularly off for a

portion of each day, a

temperature-differential sensor

that controls a small heater must

be installed. This sensor will

monitor inside and outside

temperatures simultaneously. If

the inside temperature falls to

within 5° F of the outside

temperature, the heater will come

on. This will prevent condensation

when the ventilation blower comes

on and should be used even in the

summer.

9. A controlled-air bypass system

must be installed to prevent the

temperature in the room from

falling below 40° F during

transmitter operation.

10. The blower should have two

speeds, which are thermostatically

controlled, and also be interlocked

with the transmitter.

11. The blower on high speed must be

capable of moving the required

volume of air into a half inch of

water pressure at the required

elevation. The free air delivery

method must not be used.

12. Regular maintenance of the filters,

if used, can not be

overemphasized.

13. It is recommended that a site plan

be submitted to Axcera for

comments before installation

begins.

In calculating the blower requirements,

filter size, and exhaust size, if the total

load is known in watts, 2000 CFM into ½

inch of water will be required for each

5000 watts. If the load is known in

BTUs, 2000 CFM into ½ inch of water will

be required for each 17,000 BTUs. The

inlet filter must be a minimum of seven

square feet, larger for dusty and remote

locations, for each 5000 watts or 17,000

BTUs. The exhaust must be at least four

square feet at the exhaust screen for

each 5000 watts or 17,000 BTUs.

The information presented in this section

is intended to serve only as a general

guide and may need to be modified for

unusually severe conditions. A

combination of air conditioning and

ventilation should not be difficult to

design (see Figure 3-1). System

interlocking and thermostat settings

should be reviewed with Axcera.

As with any equipment installation, it is

always good practice to consult the

manufacturer when questions arise. The

field support department at Axcera can

be contacted at (724) 873-8100.

2000-Watt VHF Low Band Transmitter Chapter 3, Installation and Setup Procedures

334B, Rev. 0 3-4

Figure 3-1. 1 kW Minimum Ventilation Configuration

3.2 Unpacking the Cabinet and Trays

Note: Air conditioning and any

related heat exhaust ducts should be

in place before continuing with the

installation of the transmitter.

Thoroughly inspect the cabinet and all

other materials upon their arrival.

Axcera certifies that upon leaving our

facility the equipment was undamaged

and in proper working order. The

shipping containers should be inspected

for obvious damage that indicates rough

handling. Check for dents and scratches

or broken switches, meters, or

connectors. Any claims against in-transit

damage should be directed to the carrier.

Inform Axcera as to the extent of any

damage as soon as possible.

Remove the cabinet and the trays from

the crates and boxes. Remove the straps

that hold the cabinet to the shipping skid

and slide the cabinet from the skid.

Remove the plastic wrap and foam

protection from around the cabinet. Do

not remove any labeling or tags from any

cables or connectors; these are

identification markers that make

assembly of the transmitter much easier.

Remove the two L-brackets, mounted on

the front panel rails, which held the trays

in place during shipment. The trays are

mounted in the cabinet using Chassis

Trak cabinet slides as shown in Figure

3-2. The tray slides are on the sides of

the three VHF amplifier trays and the

VHF exciter tray. Inspect the trays for

any loose hardware or connectors,

tightening as needed.

2000-Watt VHF Low Band Transmitter Chapter 3, Installation and Setup Procedures

334B, Rev. 0 3-5

Figure 3-2. Chassis Trak Cabinet Slides

Open the rear door and inspect the

interior of the cabinet for packing

materials and carefully remove any that

are found. Slowly slide each tray in and

out to verify that they do not rub against

each other and have no restrictions to

free movement. It may be necessary to

adjust the position of the trays to keep

them from rubbing. This is accomplished

by loosening the cabinet slide mounting

bolts that hold the front of the slide to

the mounting frame of the cabinet and

moving the tray up or down, as needed,

to correct for the rubbing.

3.3 Installing the Cabinet and Trays

The air intake to the 2000-watt

transmitter is only intended for room air.

The cabinet should be positioned for

adequate air intake and exhaust, the

opening of the rear door, if present;

access to the trays, including sliding

them out for testing, the main AC

hookup, and the installation of the output

transmission line. The cabinet should be

grounded using copper strapping

material and should be permanently

mounted to the floor of the site using the

holes in the bottom of the cabinet.

Once the cabinet is in place, and the

trays are checked for damage, the main

AC hookup can be made.

Caution: Before connecting the 220

VAC, make certain that the circuit

breaker associated with the

transmitter has been switched off.

The main AC input circuit to the 2000-

watt transmitter should be a 25-amp,

220-VAC line, using AWG 10 wire, inside

of a 1-1/4-inch conduit. The three wire

220 VAC input is connected to the AC

distribution block, white to white, black

to black and green to green by stripping

the ends of the wires, approximately ½”,

and placing them into the proper hole

and tightening the retaining screws that

holds them in place. NOTE: The 220VAC

should be connected by a qualified

electrician.

The AC is distributed to the trays through

AC plugs that connect from the power

distribution block to the rear of each tray.

The output of the (A16) coupler assembly

at (A16-J2), which is a 1-5/8” connector

and the RF output for the transmitter,

should connect to the transmission line

for the antenna system.

2000-Watt VHF Low Band Transmitter Chapter 3, Installation and Setup Procedures

334B, Rev. 0 3-6

This completes the unpacking and

installation of the 334B 2000-watt VHF

television transmitter. Refer to the setup

and operation procedures that follow

before applying power to the transmitter.

3.4 Setup and Operation Procedures

Initially, the transmitter should be turned

on with the RF output at (A16-J2) of the

coupler assembly terminated into a

dummy load of at least 2000 watts. If a

load is not available, check that the

output of the coupler assembly is

connected to the antenna.

The baseband audio and video inputs and

any remote control connections must be

made to the (A12) A/V input and remote

interface assembly. The baseband

balanced audio input connects to the

terminal block TB1 or the composite

audio input connects to the BNC jack J6.

Connect the baseband video input to the

BNC jack J2.

NOTE: If your transmitter does not

contain the 4.5 MHz composite input kit,

the following description does not pertain

to your transmitter. The baseband audio

input can remain connected when the

4.5-MHz composite input is in use

without affecting the operation of the

tray. Connect the baseband video input

to BNC jack J2 on the A/V input and the

remote interface assembly. If the

(optional) 4.5-MHz composite input kit is

purchased, connect the 4.5-MHz

composite input to the BNC jack J2. To

use the 4.5-MHz composite input, the

4.5-MHz composite input must be

connected to J2 and the baseband select

must be removed from J7-6 and J7-7 on

the rear of the VHF exciter tray. To use

the baseband video and audio inputs, the

baseband video input must be connected

to J2, the baseband audio must be

connected to the proper jack, and the

baseband select must be connected from

J7-6 and J7-7 on the rear of the VHF

exciter tray.

If the (A12) A/V input and remote

interface assembly is not present in the

system, connections are made directly to

the rear of the VHF exciter tray.

Connect the baseband balanced audio

input to the terminal block TB1 or the

composite audio input to the BNC jack J3

or J13 on the rear of the VHF exciter.

The baseband audio input can remain

connected when using the (Optional) 4.5-

MHz composite input, if present, without

affecting the operation of the tray.

Connect the baseband video input to the

BNC jack J2 or J1 also on the rear of the

VHF exciter or, if the (optional) 4.5-MHz

composite input kit is purchased, connect

the 4.5-MHz composite input to the BNC

jack J2 or J1. To use the 4.5-MHz

composite input, the 4.5-MHz composite

input must be connected to J2 or J1 and

the baseband select must be removed

from J7-6 and J7-7 on the rear of the

tray. To use the baseband video and

audio inputs, the baseband video input

must be connected to J2 or J1, the

baseband audio must be connected to

the proper jack, and a baseband select

must be connected from J7-6 and J7-7.

Switch on the main AC for the

transmitter and the circuit breakers

located on the rear of the VHF exciter,

and on the front of the three VHF

amplifier trays. On the VHF exciter tray,

switch the Operate/Standby switch to

Standby and the Auto/Manual switch to

Manual. Normal operation of the

transmitter is in Automatic, which uses

the video input to the VHF exciter as an

Operate/Standby switch. In Auto, if the

input video is lost for approximately 7

seconds, the transmitter will

automatically revert to Standby and,

when the video signal is restored, the

transmitter will quickly return to Operate.

Move the Operate/Standby switch on the

VHF exciter tray to Operate. This will

apply enables to the switching power

supplies in each of the VHF amplifier

trays. Observe that a power supply

voltage reading of +28 V is on the front

2000-Watt VHF Low Band Transmitter Chapter 3, Installation and Setup Procedures

334B, Rev. 0 3-7

panels of the VHF amplifier trays, in the

power supply position.

NOTE: If the transmitter does not switch

to Operate when the Operate/Standby

switch is placed in Operate, check that on

the (A12) A/V input and remote interface

assembly an external interlock plug is

connected to J9, with a jumper wired

from pins 21 to 22. If the (A12) A/V

input and remote interface assembly is

not present in your transmitter, check

that an external interlock plug is

connected to J11, with a jumper wired

from pins 23 to 24, on the rear of the

VHF exciter.

With the transmitter in Operate, monitor

the front panel meter of the VHF exciter

tray. In the % Visual Power position, it

should read 100%. If necessary, adjust

the screwdriver adjust power pot on the

front panel of the VHF exciter for 100%.

Check the % Reflected Power position. If

the % Reflected Power is very high,

above 10%, a problem exists with the

output coaxial lines and they will need to

be checked. A center bullet missing from

the coax lines or loose bolts on the

connections can cause this problem.

The gain and phase controls on the front

panels of the individual VHF amplifier

trays were adjusted at the factory to

obtain an output of 100% for the

transmitter and should not need to be

readjusted. The front panel readings on

the individual VHF amplifier trays may

not be the same. Refer to the Test Data

Sheet for the transmitter to compare the

final readings from the factory with the

readings on each of the trays after the

setup. If a reading is off by a significant

amount, refer to the phasing and power

adjustment procedures for the VHF

amplifier trays in Chapter 5, Detailed

Alignment Procedures, of this manual

before trying to make any adjustments.

If a dummy load is connected to the

transmitter, switch the unit to Standby

and switch off the main AC circuit

breaker. Remove the dummy load and

make all of the connections that are

needed to connect the transmitter to the

antenna. Switch the main AC circuit

breaker on and the Operate/Standby

switch to Operate. Adjust the output

power screwdriver pot to achieve an

output of 100%.

If the transmitter is already connected to

the antenna, check that the output is

100%. If necessary, adjust the power

screwdriver pot.

This completes the transmitter setup and

operation procedures for the 334B VHF

low band transmitter. The transmitter

can now be operated normally.

If a problem occurred during the setup

and operation procedures, refer to

Chapter 5, Detailed Alignment

Procedures, of this manual for more

information.

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-1

Chapter 4

Circuit Descriptions

4.1 (A4) Low Band VHF Exciter

(1070820 or 1304463 w/P.F.;

Appendix C)

NOTE: The 1304463 VHF Exciter is used

with the precise frequency system and

will contain the VCXO Assembly (1145-

1206), in place of the Channel Oscillator

Assembly (1145-1202), and the IF VCXO

Board (1248-1131), in place of the IF

Oven Oscillator Assembly (1191-1404).

4.1.1 (A4) Aural IF Synthesizer

Board, 4.5 MHz (1265-1303;

Appendix D)

The aural IF synthesizer board amplifies

and controls the levels of the three

possible audio inputs and provides a

single audio output. The balanced audio

or the composite audio input is connected

to the board while the subcarrier audio

(SCA) input can be connected at the

same time as either of the other two

inputs. The board has the 4.5-MHz

voltage-controlled oscillator (VCO) and

the aural modulation circuitry that

produces the modulated 4.5-MHz output.

The board also contains a phase lock loop

(PLL) circuit that maintains the precise

4.5-MHz separation between the aural

(41.25 MHz) and the visual (45.75 MHz)

IF frequencies.

4.1.1.1 Balanced Audio Input

The first of the three possible baseband

audio inputs to the board is a 600Ω-

balanced audio input (+10 dBm low gain

or 0 dBm high gain) that enters through

jack J2, pins 1 (+), 2 (GND), and 3 (-).

The input is then buffered by U1B and

U1C. The diodes CR18 and CR19 are

transient voltage suppressors that

protect the board from any surges or

transients that may occur on the

balanced audio input lines. The Diodes,

CR1 to CR4, protect the input stages of

U1B and U1C if an excessive signal level

is applied to the board. The outputs of

U1B and U1C are applied to the

differential amplifier U1A that eliminates

any common mode signals (hum) on its

input leads. A pre-emphasis of 75 µs is

provided by R11, C11, and R10 and can

be eliminated, if not needed, by

removing the jumper W5 on J5. The

signal is then applied to the amplifier

U1D whose gain is controlled by the

jumper W3 on J11. The Jumper is

positioned according to the input level of

the audio signal (0 or +10 dBm). If the

input level is approximately 0 dBm, the

mini-jumper should be in the high gain

position between pins 1 and 2 of J11. If

the input level is approximately +10

dBm, the mini-jumper should be in low

gain position which is between pins 2 and

3 of J11. The balanced audio is then

connected to the buffer amplifier U2A

whose input level is determined by the

setting of balanced audio gain pot R13.

The output of the amplifier stage is wired

to the summing point at U2D pin 13.

4.1.1.2 Composite Audio Input

The second possible audio input to the

board is the composite audio (stereo)

input at BNC jacks J3 and J13. The two

jacks are loop-through connected.

Therefore, the audio can be used in

another application by connecting to the

unused jack and moving the jumper W4

to J12 between pins 2 & 3. The jumper

W4 on jack J12 provides a 75Ω-input

impedance when the jumper is on J12

pins 1 and 2 and a high impedance when

it is on pins 2 and 3. The diodes CR20

and CR21 are transient voltage

suppressors that protect the board from

surges and transients on the composite

audio input lines. Diodes CR9 to CR12

protect the input stages of U6A and U6B

if an excessive signal level is applied to

the board. The outputs of U6A and U6B

are connected to the differential amplifier

U2C, which eliminates any common

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-2

mode signals (hum) that may occur on

its input leads. The composite audio

input signal is applied to the amplifier

U2B whose gain is controlled by the

composite audio gain pot R17. The

composite audio signal is then connected

to the summing point at U2D pin 13.

4.1.1.3 Subcarrier Audio Input

The third possible input to the board is

the subcarrier audio (SCA) input at the

BNC jack J4. The SCA input has an input

impedance of 75Ω that can be eliminated

by removing the jumper W2 from J14.

The SCA input is bandpass filtered by

C66, C14, R22, C15, C67, and R23 and

fed to the buffer amplifier U3A pin 3.

The amplified signal is then applied

though the SCA gain pot R24 to the

summing point at pin 13 of U2D.

4.1.1.4 Audio Modulation of the VCO

The balanced audio or the composite

audio and/or the SCA audio signals, are

fed to the common junction of resistors

R14, R20, and R27 that connect to the

summing point at pin 13 of the amplifier

U2D. The output audio signal at pin 14

of U2D is typically .8 Vpk-pk at a ±25-

kHz deviation with a balanced audio input

or .8 Vpk-pk at ±75-kHz deviation with a

composite audio input, as measured at

TP1. This audio signal is applied to the

VCO U10. A sample of the deviation

level is amplified, detected by U7A and

U7B, and connected to J10 on the board,

which is cabled to the front panel meter

through the transmitter control board.

The audio is applied through C64, a

frequency response adjustment, to CR13

to CR16, which are varactor diodes that

frequency modulate the audio signal onto

the generated 4.5-MHz signal in U10.

U10 is the 4.5-MHz VCO that generates

the 4.5-MHz continuous wave (CW)

signal. The output frequency of this

signal is maintained and controlled by the

correction voltage output of the PLL IC

U5. The audio-modulated, 4.5-MHz

signal is fed to amplifiers U11A and

U11B. The output of U11B is connected

to the 4.5-MHz output jacks at J7 and J8.

4.1.1.5 Phase Lock Loop (PLL) Circuit

A sample of the signal from the 4.5-MHz

aural VCO at the output of U11A is

applied to the PLL IC U5 pin 1, the Fin

connection. In U5, the signal is divided

down to 50 kHz and is compared to a 50-

kHz reference signal. The 50-kHz

reference signal is a divided-down

sample of the visual IF, 45.75-MHz signal

generated on the IF carrier oven

oscillator board, that is applied to pin 27,

the oscillator in connection, on the PLL

chip through jack J6 on the board. These

two 50-kHz signals are compared in the

IC and the fV

output at pin 8 and the fR

output at pin 7 are applied to the

differential amplifier U3B. The output of

U3B is fed back through CR17 to the 4.5-

MHz VCO IC U10, which sets up a PLL

circuit, therefore any change in frequency

will be corrected by the AFC error

voltage. The 4.5-MHz VCO, using the

PLL circuit, will maintain the extremely

accurate 4.5-MHz separation between the

visual 45.75 MHz and aural 41.25 MHz IF

signals.

The PLL chip U5 also contains an internal

lock detector that indicates the status of

the PLL circuit. When U5 is in a "locked"

state, pin 28 goes high and causes the

green LED DS1 to illuminate. If the 4.5-

MHz VCO and the 45.75-MHz oscillator

become "unlocked," out of the capture

range of the PLL circuit, pin 28 of U5 will

go to a logic low and cause the red LED

DS2 to light. A mute output signal from

Q3 (unlock mute) will be applied to jack

J9. This mute is connected to the

transmitter control board.

4.1.1.6 Voltage Requirements

The ±12 VDC needed for the operation of

the board enters through jack J1. The

+12 VDC is connected to J1-3 and

filtered by L2, C3, and C4 before it is

connected to the rest of the board. The

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-3

-12 VDC is connected to J1-5 and filtered

by L1, C1, and C2 before it is connected

to the rest of the board. Two

connections of the +12 VDC are to U8

and U9, which are 5-volt regulator ICs

that provide the voltage to the U10 and

U5 ICs.

4.1.2 (A5) Sync Tip Clamp/

Modulator Board (1265-1302;

Appendix D)

The sync tip clamp/modulator board is

divided into five circuits: the main video

circuit, the sync tip clamp circuit, the

visual modulator circuit, the aural IF

mixer circuit, and the diplexer circuit.

The sync tip clamp/modulator board

takes the baseband video or the 4.5-MHz

composite input that is connected to the

video input jack, either J1 or J2, which

are loop-through connected, and

produces a modulated visual IF + aural

IF output at output jack J20 on the

board. The clamp portion of the board

maintains a constant peak of sync level

over varying average picture levels

(APL). The modulator portion of the

board contains the circuitry that

generates an amplitude modulated

vestigial sideband visual IF signal output

that is made up of the baseband video

input signal (1 Vpk-pk) modulated onto

an externally generated 45.75-MHz IF

carrier frequency. The visual IF signal

and the aural IF signal are combined in

the diplexer circuit to produce the visual

IF + aural IF output that is connected to

J20, the IF output jack of the board.

4.1.2.1 Main Video Signal Path (Part 1 of

The baseband video or the 4.5-MHz

composite input connects to the board at

J2. J2 is loop-through connected to J1

and terminated into 75Ù, if the jumper

W4 is on jack J3. With jumper W4

removed, the input can be connected to

another transmitter through J1.

Test point TP1 is provided to monitor the

level of the input. The input is fed to the

non-inverting and inverting inputs of

U1A, a differential amplifier that

minimizes any common-mode hum that

may be present on the incoming signal.

Diodes CR1 to CR4 form a voltage-limiter

network in which, if the input voltages

exceed the supply voltages for U1A, the

diodes conduct, preventing damage to

U1A. CR1 and CR3 conduct if the input

voltage exceeds the negative supply and

CR2 and CR4 conduct if the input voltage

exceeds the positive supply voltage.

The video output of U1A is connected to

J22 on the board. Normally, the video at

J22 is jumpered to J27 on the board. If

the optional 4.5-MHz composite input kit

is purchased, the 4.5-MHz composite

signal at J22 connects to the external

composite 4.5-MHz filter board and the

4.5-MHz bandpass filter board. These

two boards provide the video-only signal

to J27 and the 4.5-MHz intercarrier signal

to J28 from the 4.5-MHz composite input.

The video through the video gain pot R12

is typically adjusted for 1 Vpk-pk at TP2

and connects to amplifier U1B.

The output of U1B, if the delay equalizer

board is present in the tray, connects the

video from J6 pin 2, to the external delay

equalizer board and back to the sync tip

clamp/modulator board at J6 pin 4. If

the delay equalizer is not present, the

video connects through jumper W1 on J5,

pins 1 and 2. The delay equalizer board

plugs directly into J6 on the sync tip

clamp/modulator board. The video from

J6 pin 4 is connected through the jumper

W1 on J5 pins 2 and 3, to the amplifier

Q1. The output of Q1 connects to Q2.

The base voltage of Q2 is set by the DC

offset voltage output of U3B, which is the

sync tip clamp circuit output.

4.1.2.2 Sync Tip Clamp Circuit

The automatic sync tip clamp circuit is

made up of U4A, Q7, U3B, and

associated components. The circuit

begins with a sample of the clamped

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-4

video that is split off from the main video

path at the emitter of Q3. The video

sample is buffered by U3A and connected

to U4A. The level at which the tip of sync

is clamped, approximately -1.04 VDC, as

measured at TP2, is set by the voltage-

divider network connected to U4A. If the

video level changes, the sample applied

to U4A changes. If the jumper W7 on J4

is in the Clamp-On position, the voltage

from the clamp circuit that is applied to

the summing circuit at the base of Q2 will

change and bring the sync tip level back

to approximately -1.04 VDC. Q7 will be

turned off and on by the peak of sync

voltage level that is applied to U4A. The

capacitors C14, C51, C77, and C41 will

charge or discharge to the new voltage

level, which biases U3B more or less,

through the jumper W7 on J4 when in

the Auto Clamp-On position. U3 will

increase or decrease its output, as

needed, to bring the peak of sync back to

the correct level that is set by R152 and

R12. This voltage level is applied

through U3B to Q2. In the Manual

position, jumper W7 on J4 is in the

Clamp-Off position, between pins 1 and

2, and the adjustable resistor R41

provides the manual clamp bias

adjustment for the video that connects to

Q2.

The Jumper W6 on jack J35 must be in

the Normal position, between pins 2 and

3, for the clamp circuit to operate with a

normal non-scrambled signal. If a

scrambled signal is used, the tray is

operated with jumper W6 in the Encoded

position, connected between pins 1 and

The clamp circuit is set by adjusting the

depth of modulation pot R152 for the

correct depth of modulation as measured

at TP2. Depending on the input video

level, the waveform as measured at TP2

may not be 1 Vpk-pk. If W7 on J4 is

moved to the Clamp-Off (Manual)

position, between pins 1 and 2, the

clamp level is adjusted by R41 and will

not automatically be clamped to the set

level.

The output of buffer amplifier U3A drives

the sync tip clamp circuit consisting of

the differential amplifier U4A, FET Q7,

and buffer amplifier U3B. U4A is biased

by R124, R125, R184, R152, and R126

so that the clamped voltage level at the

peak of sync is approximately -1.04 VDC

as measured at TP2.

4.1.2.3 Main Video Signal Path (Part 2 of

The clamped video from Q2 is connected

to the white clipper circuit Q3. Q3 is

adjusted by R20 and set to prevent video

transients from overmodulating the video

carrier. The clamped video is connected

to the sync clipper circuit Q4, which is

adjusted by R24. Q4 limits the sync to

-40 IRE units. The corrected video

output of the emitter follower Q4 is wired

to the unity gain amplifier U2A that

provides a low impedance, clamped video

output at pin 1, which can be measured

at TP2.

4.1.2.4 Visual Modulator Circuit

The clamped video signal from U2A is

split. One part connects to a metering

circuit, consisting of U20 and associated

components, which produces a video

output sample, white level, at J8-6 that

connects through the transmitter control

board to the front panel meter for

monitoring. The other clamped video

path from U2A is through a sync stretch

circuit that consists of Q5 and Q6. The

sync stretch circuit contains R48 that

adjusts the sync stretch magnitude

(amount) and R45 that adjusts the cut-in

point. This sync stretch adjustment

should not be used to correct for output

sync problems, but it can be used for

input video sync problems. The output of

the sync stretch circuit connects to pin 5,

the I input of mixer Z1.

The video signal is heterodyned, in mixer

Z1, with the 45.75 MHz visual IF CW

signal. The visual IF CW signal enters

the board at jack J15 and is connected to

U9, where it is amplified and wired to pin

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-5

1, the L input of mixer Z1. The

adjustable capacitor C78 and resistor R53

are set up to add a small amount of

incidental carrier phase modulation

(ICPM) correction to the output of the

mixer stage to compensate for any non-

linearities generated by the mixer.

The modulated 45.75-MHz RF output of

mixer Z1, at pin 4, the R output, is

amplified by U5 and is fed to J18 the

double sideband visual IF output jack.

The level at this output jack is adjusted

by R70, typically –4 to –10 dBm. J18 is

the visual IF loop-through output jack

that is normally jumpered by W10 to J19

on the board. If the (Optional) visual IF

loop-through kit is purchased, the visual

is connected out of the board to any

external IF processor trays and then back

to the board.

After any external processing, the

modulated visual IF, double-sideband

signal re-enters the board through J19.

The visual IF from J19 is amplified by

U10 and U11 and routed through the

vestigial sideband filter network,

consisting of T1, FL1, and T2, that

produces a vestigial sideband visual IF

signal output. The filtered vestigial

sideband visual IF is amplified by U7 and

connected to a T-type attenuator. R62 is

adjustable to set the visual IF gain, which

is the amount of visual IF signal that is

coupled to the amplifier IC U8. R63 and

C30 are adjusted for the best VSBF

frequency response. The amplified IF

signal output of U8 is fed to the input of

the diplexer circuit that consists of R76,

L13, and L12. A detected voltage sample

of the visual IF is available at the test

point TP5.

4.1.2.5 41.25-MHz Aural IF Circuit

The modulated 41.25-MHz aural IF is

created on this board by mixing the

modulated 4.5-MHz aural intercarrier

signal, produced by the aural IF

synthesizer board or by the optional

composite 4.5-MHz filter board, with the

45.75-MHz CW signal produced by the

45.75-MHz IF carrier oven oscillator

board or the IF VCXO board, in a precise

frequency system. The modulated

baseband 4.5-MHz aural intercarrier

signal enters the board at J14, baseband

4.5-MHz Input, and for normal operation

connects through the jumper W8 on J32

pins 1 and 2, IF Relay Disabled, through

the jumper W3 on J7 pins 2 and 3,

Internal 4.5-MHz, to Z2 pin 5, the I input

of the Mixer.

If both composite 4.5-MHz and baseband

4.5-MHz is to be used in your system,

then the relay K1 must be enabled. This

is accomplished by moving the jumper

W8 on J32 to between pins 2 and 3.

Both inputs, the modulated baseband

4.5-MHz aural intercarrier input from J14

and the Composite 4.5-MHz Input from

J28 connect to the IF relay K1. The

jumper W2 on J30 must be between pins

1 and 2, baseband select off, for external

operation of the relay. Now the relay is

controlled by a baseband select, Low,

that connects to J31 Pin 3. With the

baseband select, Low, present at J31 pin

3, the relay is energized and applies the

baseband 4.5 MHz to the mixer Z2 and

DS1 the baseband indicator will be lit.

With the baseband select removed, not

present at J31 pin 3, the relay is de-

energized and applies the composite 4.5

MHz to the mixer Z2 and DS1 the

baseband indicator will not be lit.

The Jumper W3 on J7 determines

whether the 4.5-MHz used by the board

is internally generated, either the

baseband or composite inputs, or from

an external source. With the jumper W3

connected between pins 2 and 3, the 4.5

MHz from the aural IF synthesizer board

or from the 4.5-MHz composite input is

connected to the mixer Z2. With the

jumper W3 connected between pins 1

and 2, the external 4.5 MHz input is

connected to the mixer Z2. The external

4.5-MHz signal enters the board at J12

and is fed through the gain pot R88 to

the amplifier IC U13A. The amplified 4.5-

MHz is then connected to J7 through the

jumper W3 to the mixer.

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-6

The Mixer Z2 heterodynes the aural-

modulated, 4.5-MHz signal with the

45.75-MHz CW signal to produce the

modulated 41.25-MHz aural IF signal

output.

The output of the mixer at pin 4, the R

output, is fed to a bandpass filter that is

tuned to pass only the modulated 41.25-

MHz aural IF signal. The bandpass

filtered signal is fed to jack J16, the

41.25-MHz aural IF loop-through output

jack of the board. For normal operation,

the 41.25-MHz signal is jumpered by a

coaxial cable W11 from J16 to J17 on the

board. If the (Optional) aural IF loop-

through kit is purchased, the Aural IF

41.25-MHz signal is connected to the rear

of the tray, to which any Aural IF

processing trays can be connected, and

then back to jack J17 on the board.

The modulated 41.25-MHz aural IF signal

from J17 is connected through an

impedance matching transformer T3,

75Ù to 50Ù, to the amplifier ICs U15 and

U16. The amplified output is connected

to the attenuator matching circuit that is

adjusted by R85. R85 increases or

decreases the level of the Aural IF 41.25

MHz that sets the A/V ratio in the

diplexer circuit.

4.1.2.6 Diplexer Circuit

The diplexer circuit takes the modulated

45.75-MHz visual IF, that connects to the

junction of R76 and L12, and the

modulated 41.25-MHz aural IF, that

connects to the junction of R76 and L13,

and combines them to produce the

45.75-MHz + 41.25-MHz IF output. The

combined 45.75-MHz + 41.25-MHz IF

signal is amplified by U12 and connected

to J20 the combined IF output jack of the

board. A sample of the combined IF

output is provided at J21.

If an (Optional) NICAM input is used, it

connects to J36 on the board. The level

of the NICAM signal is set by R109 before

it is fed to the diplexer circuit consisting

of L28, L29, and R115. This circuit

combines the NICAM signal with the

45.75-MHz visual IF + 41.25-MHz aural

IF signal.

4.1.2.7 Operational Voltages

The +12 VDC needed to operate the sync

tip clamp modulator board enters the

board at J23 pin 3, and is filtered by L26,

L33, and C73 before it is connected to

the rest of the board.

The -12 VDC needed to operate the

board enters the board at J23 pin 5, and

is filtered by L27 and C74 before being

fed to the rest of the board.

4.1.3(Optional) (A6) Delay Equalizer

Board (1227-1204; Appendix D)

The (Optional) delay equalizer board

provides a delay to the video signal,

correction to the frequency response, and

amplification of the video signal.

The video signal enters the board at J1-2

and is connected to a pi-type, low-pass

filter consisting of C16, L7, and C17.

This filter eliminates any unwanted

higher frequencies from entering the

board. The output of the filter is

connected to the amplifier stage U1,

whose gain is controlled by R29. The

video output of the amplifier stage is

wired to the first of four delay-equalizing

circuits that shape the video signal to the

FCC specification for delay equalization or

to the desired shape needed for the

system. The board has been factory-

adjusted to the FCC specification and

should not be readjusted without the

proper equipment.

Resistors R7, R12, R17, and R22 adjust

the sharpness of the response curve,

while inductors L1, L2, L3, and L4 adjust

the position of the curve. With a delay

equalizer test generator signal or a sine

x/x video test pattern input, the resistors

and inductors can be adjusted, while

monitoring a Tektronix VM700 test

measurement set, until the desired FCC

delay equalization curve or system curve

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-7

is attained. The delay-equalized video

signal output of the board is at J1-4. A

sample of the delayed video signal is

provided at J2 on the board and can be

used for testing purposes.

The ±12 VDC needed to operate the

board enters the board at J1. The +12

VDC connects to J1-9, which is filtered by

L5 and C11 before it is directed to the

rest of the board. The -12 VDC connects

to J1-6, which is filtered by L6 and C12

before it is directed to the rest of the

board.

4.1.4 (A7) IF Carrier Oven Oscillator

Board (1191-1404; Appendix D)

NOTE: If the precise frequency kit is

present in your transmitter, the IF VCXO

Board (1248-1131) will be used.

The IF carrier oven oscillator board

generates the visual IF CW signal at

45.75 MHz for NTSC system "M" usage.

The 45.75 MHz crystal Y1 is the principal

device that determines the operating

frequency and is the most sensitive in

terms of temperature stability, therefore

it is enclosed in an oven. +12 VDC is

applied through jack J10 to the crystal

oven HR1, which is preset to operate at

60° C. The oven encloses the crystal Y1

and stabilizes the crystal temperature.

The crystal operates in an oscillator

circuit consisting of the transistor Q1 and

its associated components. Feedback is

provided through a capacitor voltage

divider, consisting of C5 and C6, that

operates the crystal in a common-base

amplifier configuration using Q1. The

operating frequency of the oscillator can

be adjusted by the variable capacitor

C17. The oscillator circuit around Q1 has

a separate regulated voltage, 6.8 VDC,

which is produced from the +12 VDC by

a combination of the dropping resistor R4

and the zener diode VR1. The output of

the oscillator at the collector of Q1 is

capacitively coupled through C8 to the

base of Q2. The small value of C8, 10

pF, prevents the oscillator from being

loaded down by Q2.

Q2 is operated as a common-emitter

amplifier stage whose bias is provided

through R8 from the +12 VDC line. The

output of Q2, at its collector, is split

between two emitter-follower transistor

stages, Q3 and Q4. The output of Q3 is

taken from its emitter through R11, to

establish an approximate 50-ohm source

impedance, through C11 to J3, the main

output jack of the board. This 45.75-

MHz signal is approximately +5 dBm in

level. The output is directed to a visual

modulator circuit located on the

clamp/modulator board. The second

output from the collector of Q2 is fed to

the base of Q4, an emitter follower

transistor. Q4 drives two different output

circuits. One output is directed through

the voltage dividers R14 and R15 to jack

J2 and is normally fed to a frequency

counter. While monitoring J2 the

oscillator can be set exactly on the

operating frequency (45.75 MHz) by

adjusting C17. The output at J2 is

approximately -2 dBm in level, which is

sufficient to drive most frequency

counters. The other output of Q4

connects to the prescaler chip U1, which

divides the signal by 15. The output of

U1 is applied to U2, a programmable

divider IC. U2 is programmed through

pins 11 to 20 to divide by 61, which

results in a 50-kHz signal at pin 9 that is

available as an output at J1. This 50 kHz

reference output is generally used in

systems where the visual IF carrier oven

oscillator is used as the reference for a

PLL circuit. An example of this is when

the PLL circuit locks the aural VCO on the

aural IF synthesizer board. The 50-kHz

CMOS output at jack J1 is not capable of

achieving enough drive level for a long

coaxial cable length. As a result, when a

long coaxial cable is needed, the output

at jack J5 is utilized. The push-pull

transistor stage Q5 and Q6, along with

emitter resistor R18, provide a large load

output capability at J5.

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-8

The stages U1, U2, U3, Q5, and Q6 are

from the +12 VDC line voltage using the

voltage-dropping resistor R16 and the

zener diode VR2.

The +12 VDC input to the board is

applied through the jack J4 at pin 3. The

voltage is isolated from any RF, which

may occur in the +12 VDC line, through

the use of the RF choke L2 and the filter

capacitor C10.

4.1.4.1 (Optional) (A7) IF VCXO

Board (1248-1131; Appendix D)

NOTE: If a precise frequency kit is not

present in your transmitter, the IF Carrier

Oven Oscillator Board (1191-1404) will

be used.

The IF Carrier VCXO Board generates the

Visual IF CW signal at 45.75 MHz for

NTSC System "M" usage.

The 45.75 MHz crystal Y1 is the principal

device that determines the operating

frequency and is the most sensitive in

terms of temperature stability, therefore

it is enclosed in an oven. +12 VDC is

applied through jack J10 to the crystal

oven HR1, which is preset to operate at

60° C. The oven encloses the crystal Y1

and stabilizes the crystal temperature.

The crystal operates in an oscillator

circuit consisting of the transistor Q1 and

its associated components. Feedback is

provided through a capacitor voltage

divider, consisting of C5 and C6, which

operates the crystal in a Common Base

Amplifier configuration using Q1. The

operating frequency of the Oscillator is

adjustable by the variable capacitor C22

and maintained for accuracy by the AFC

voltage, from the external Precise

Frequency Tray, that connects to J13.

The AFC voltage input connects through

J13 and then the combination of the

dropping resistor R23 and the Zener

Diode VR1 to the oscillator circuit. The

output of the oscillator at the collector of

Q1 is capacitively coupled through C8 to

the base of Q2. The small value of C8,

10 pF, prevents the oscillator from being

loaded down by Q2.

Q2 is operated as a Common Emitter

Amplifier stage whose bias is provided

through R8 from the +12 VDC line. The

output of Q2, at its collector, is split

between two Emitter Follower Transistor

Stages, Q3 and Q4. The output of Q3 is

taken from its Emitter through R11 to

establish an approximate 50Ù source

impedance thru C11 to J3 the Main

Output Jack of the board. The 45.75

MHz signal is approximately +5 dBm in

level. A Sample of the Main O/P is

provided at J11. The second output

from the collector of Q2 is fed to the

Base of the Emitter Follower Transistor,

Q4.

Q4 drives two different output circuits.

One output is directed through a voltage

divider R14 and R15 to Jack J2 that is

typically fed to a Frequency Counter.

The output level at J2 is approximately

-2 dBm, which is sufficient to drive most

Frequency Counters. The other output of

Q4 connects to (U1) a Prescaler Chip that

divides the signal by 15. The output of

U1 is applied to (U2) a Programmable

Divider IC. U2 is programmed through

Pins 11-20 to divide by 61, which results

in a 50 kHz signal at Pin 9 that is

available as an output at J1. The output

of 50 kHz is generally used in systems

where the Visual IF Carrier Oven

Oscillator is used as the reference for a

PLL Circuit. An example is the PLL Circuit

using the Aural IF Synthesizer Board and

the Aural VCO. The 50 kHz CMOS Output

at Jack J1 is not capable of enough drive

level for a long coaxial cable length,

therefore, when a long coaxial cable is

needed, the output at Jack J5 is utilized.

The Push-Pull transistor stage Q5 and

Q6, along with the Emitter resistor R18,

provide a large load output capability at

J5.

The stages U1, U2, U3, Q5 and Q6 are

from the +12 VDC line voltage and the

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-9

voltage dropping resistor R16 and Zener

Diode VR2.

The +12 VDC input to the board is

applied through Jack J4 Pin 3 and is

isolated from any RF, which may occur

on the +12 VDC Line, through the use of

the RF choke L2 and the filter capacitor

C10.

4.1.5 (A8) ALC Board, NTSC (1265-

1305; Appendix D)

The automatic level control (ALC) board

provides the ALC and amplitude linearity

correction of the IF signal. The ALC

adjusts the level of the IF signal through

the board to control the output power of

the transmitter.

The visual + aural IF input (0 dBm)

signal, from the clamp/modulator board,

enters the board at the modulator IF

input jack J32. If the (Optional) receiver

tray is present, the visual + aural IF

input (0 dBm) from the receiver tray

connects to receiver IF input jack J1.

4.1.5.1 Local Modulator Select Enabled

(Normal Operation with the Modulator IF

as the Input)

The modulator IF input connects to the

relay K3 and the receiver IF input

connects to the relay K4. The two relays

are controlled by the position of the local

Modulator Select enable/disable jumper

W11 on J29. The normal operation of

the transmitter uses the Modulator IF

input at J32. The jumper W11 connected

between pins 2 and 3 is the normal

operating position for the board. This

sets the board to the local Modulator

enable position, which is both relays de-

energized and the Modulator IF Input

connected to the rest of the board. DS5

the Modulator Enable LED will be lit.

4.1.5.2 Local Modulator Select Disabled

(Operation with the ability to select either

the Modulator IF or the Receiver IF as

the Input)

If a receiver tray is part of your system,

then the relays need to be controlled by

the Modulator Select command that is

connected to J30 on the board, so that

either the receiver IF or the modulator IF

can be used by the board. The position

of the Modulator select enable/disable

jumper W11 on J29 provides for the

Modulator Select command at J30 to

control the operation of the relays. With

the jumper W11 on J29, between pins 1

and 2, the Modulator Select command at

J30 controls the operation of the relays

and with the jumper W11 on J29,

between pins 2 and 3, the modulator is

selected all of the time and DS5, the

modulator enable LED, will be lit.

4.1.5.3 Modulator IF Selected

(With the Local Modulator Select

Disabled)

The modulator is normally selected by

J11-10 and J11-28 on the rear of the VHF

exciter tray, wired to J30 on the board,

connected together. This makes J30 go

low and causes relays K3 and K4 to de-

energize. When K4 is de-energized, it

connects the receiver IF input at J1 to

50Ù. When K3 is de-energized, it

connects the modulator IF input at J32 to

the rest of the board and the Modulator

Enable LED DS5 will be illuminated.

4.1.5.4 Receiver IF Selected

(With the Local Modulator Select

Disabled)

The receiver is normally selected when

J11-10 and J11-28 on the rear of the VHF

exciter tray, connected to J30 on the

board, are not connected together. This

makes J30 high and causes the relays K3

and K4 to energize. When K4 is

energized, it connects the receiver IF

input at J1 to the rest of the board.

When K3 is energized, it connects the

modulator IF input at J32 to 50Ù and the

Modulator Enable LED DS5 will not be

illuminated.

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-10

4.1.5.5 Main IF Signal Path (Part 1 of 3)

The selected visual + aural IF input (0

dBm) signal is split at L1 and L2, with

one half of the signal flowing through L1

and entering a bandpass filter that

consists of L3, L4, C4, L5, and L6. This

bandpass filter can be tuned with C4 and

is substantially broader than the IF signal

bandwidth. It is used to slightly steer the

frequency response of the IF to make up

for any small discrepancies in the

frequency response in the stages that

precede this point. The filter also serves

the additional function of rejecting

unwanted frequencies that may occur if

the tray cover is off and the tray is in a

high RF environment. If this is the case,

the transmitter will have to be serviced

with the tray cover off in spite of the

presence of other RF signals. The filtered

IF signal is fed through a pi-type

matching pad consisting of R2, R3, and

R4 to the pin-diode attenuator circuit

consisting of CR1, CR2, and CR3.

4.1.5.6 Input Level Detector Circuit

The other part of the split IF input is

connected through L2 and C44 to U7, an

IC amplifier that is the first stage of the

input level detector circuit. The amplified

IF is fed to T4 that is a step-up

transformer, which feeds a diode

detector CR14. The positive-going

detected signal is then low-pass filtered

by C49, L18, and C50. This allows only

the video with positive sync to be applied

through the emitter follower Q1. The

signal is then connected to the detector

CR15 that produces a peak of sync

voltage, which is applied to the op-amp

U9A. There is a test point at TP3 that

provides a voltage reference check of the

input level. The detector serves the dual

function of providing a reference that

determines the input IF signal level to

the board and also serves as an input

threshold detector. The input threshold

detector prevents the automatic level

control from reducing the attenuation of

the pin-diode attenuator to minimum

(the maximum signal) if the IF input to

the board is removed. Without the

threshold detector, and with the pin-

diode attenuator at minimum, when the

signal is restored it will overdrive the

stages following this board. The ALC,

video loss cutback, and the threshold

detector circuits will only operate when

jumper W3 on jack J6 is in the Auto

position, between pins 1 and 2.

As part of the threshold detector

operation, the minimum IF input level, as

measured at TP3, is fed through the

detector diode CR15 to the op-amp IC

U9A pin 2. The reference voltage for the

op-amp is determined by the voltage

divider that consists of R50 and R51, off

the +12 VDC line. When the detected

input signal level at U9A pin 2, falls

below this reference threshold,

approximately 10 dB below the normal

input level, the output of U9A at pin 1

goes to the +12 VDC rail. This high is

connected to the base of Q2. At this

point, Q2 is forward biased and creates a

current path from the -12 VDC line

through the red LED DS1, the input level

fault indicator, which lights, the resistor

R54, and the transistor Q2 to the +12

VDC line.

The high from U9A also connects through

the diode CR16 to U9B pin 5, whose

output at pin 7 goes high. The high

connects through the range adjust pot

R74 to J20, which connects to the front

panel mounted power adjust pot. This

high also connects to U10A pin 2, and

causes it to go low at U10A pin 1. The

low is applied through the jumper W3 on

J6, when in auto, to the pin-diode

attenuator circuit, CR1 – CR3, that cuts

back the IF level and, therefore also the

output power level, to 0. When the input

signal level increases above the threshold

level, the output power will increase, as

the input level increases, until normal

output power is reached.

The video input level as measured at TP3

is also fed to a sync-separator circuit,

consisting of U8, CR17, Q3, and

associated components, and then to a

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-11

comparator circuit made up of U9C and

U9D. The reference voltage for the

comparators is determined by a voltage

divider network consisting of R129, R64,

R65, R66, and R130, off the -12 VDC

line. When the input signal level falls

below this reference threshold, which

acts as a loss of sync detector circuit, the

outputs of U9C and U9D move towards

the -12 VDC rail. The low output is split

with one part connecting to and biasing

on the transistor Q5. A current path is

then established from the +12 VDC line

through Q5, the resistors R69, R137, and

the red LED DS3, the video loss indicator,

which lights. When Q5 is biased on, it

applies a high to the gates of Q6 and Q7.

This causes them to conduct and apply

video loss fault pull-down outputs to J18

pins 5 and 2.

The other low output of U9C and U9D is

connected through CR20 to jack J5,

which controls the cutback enable/disable

operation. The jumper W2 on J5, in the

Cutback Enable position, which is

between pins 2 and 3, connects the low

to the base of Q4 that is forward-biased.

If the jumper W2 is in the Disable

position, between pins 1 and 2, the auto

cutback will not operate. With Q4 biased

on, a level determined by the setting of

the cutback level pot R71, which is set at

the factory to cut back the output to

approximately 25%, is applied to U9B pin

5. The output of U9B at pin 7 goes low

and is applied through the power adjust

pot to U10A pin 2, whose output goes

low. This low is applied to the pin-diode

attenuator, CR1-CR3, to cut back the

level of the output to the cut back value

of approximately 25%.

4.1.5.7 Pin-Diode Attenuator Circuit

The input IF signal to the board is fed to

a pin-diode attenuator circuit that

consists of CR1, CR2 & CR3. Each of the

pin diodes contains a wide intrinsic

region, which makes the diodes function

as voltage variable resistors at this

intermediate frequency. The value of the

resistance is controlled by the DC bias

applied to the diodes. The pin diodes are

configured in a pi-type attenuator

configuration where CR1 is the first shunt

element, CR3 is the series element, and

CR2 is the second shunt element. The

control voltage, which can be measured

at TP1, originates either from the ALC

circuit, when jumper W3 on J6 is in the

ALC Auto position, between pins 1 and 2,

or from the variable resistor R87 when

the jumper is in the Manual Gain

position, between pins 2 and 3. In the

pin-diode attenuator circuit, a current

path exists from J6 through R6 and then

through the diodes of the pin attenuator.

Changing the amount of current through

the diodes by forward biasing them,

decreases their resistances which

increases the IF output level of the

board.

There are two extremes of attenuation

ranges for the pin-diode attenuators. In

the minimum attenuation case, the

voltage, as measured at TP1, approaches

the +12 VDC line. There is a current

path created through R6, through series

diode CR3, and finally through R9 to

ground. This path forward biases CR3

and causes it to act as a relatively low-

value resistor. In addition, the larger

current flow increases the voltage drop

across R9 that tends to turn off the

diodes CR1 and CR2 and causes them to

act as high-value resistors. In this case,

the shunt elements act as a high

resistance and the series element acts as

a low resistance to represent the

minimum loss condition of the attenuator

(maximum signal output). The other

extreme case occurs as the voltage at

TP1 is reduced and goes towards ground

or even slightly negative. This tends to

turn off (reverse bias) diode CR3, the

series element, causing it to act as a

high-value resistor. An existing fixed

current path from the +12 VDC line

through R5, CR1, CR2, and R9, biases

the series element CR3 off and the shunt

elements, diodes CR1 and CR2 on,

causing them to act as relatively low-

value resistors. This represents the

maximum attenuation case of the pin

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-12

attenuator (minimum signal output). By

controlling the value of the voltage

applied to the pin diodes, the IF signal

level is maintained at the set level.

4.1.5.8 Main IF Signal Path (Part 2 of 3)

When the IF signal passes out of the pin-

diode attenuator through C11, it is

applied to the modular amplifier U1. This

device includes within it the biasing and

impedance matching circuits that makes

it operate as a wide-band IF amplifier.

The output of U1, at jack J2, is available,

as a sample of the pre-correction IF for

troubleshooting purposes and system

setup. The IF signal is then connected to

the linearity corrector portion of the

board.

4.1.5.9 Linearity Corrector Circuits

The linearity corrector circuits use three

stages of correction to correct for any

amplitude non-linearities in the IF signal.

Each stage has a variable threshold

control adjustment, R34, R37, or R40,

and a variable magnitude control

adjustment, R13, R18, or R23. The

threshold control determines the point at

which the gain is changed and the

magnitude control determines the

amount of gain change that occurs once

the breakpoint is reached. Two reference

voltages are needed for the operation of

the corrector stages. The Zener diode

VR1 using R33 and R135 provides a +6.8

VDC reference from +12 VDC. The

diodes CR11 and CR12 provide a .9 VDC

reference that temperature compensates

for the two diodes in each corrector

stage.

The linearity corrector stages begin

operation when an IF signal is applied to

transformer T1, which doubles the

voltage swing by means of a 1:4

impedance transformation. Resistors

R14, R15, and R16 form an L-pad that

lowers the level of the signal. The

amount that the level is lowered is

adjusted by adding more or less

resistance, using R13, in parallel with the

L-pad resistors. R13 is only in parallel

when the signal reaches a level large

enough to turn on the diodes CR4 and

CR5. When the diodes turn on, current

flows through R13, putting it in parallel

with the L-pad. When R13 is put in

parallel with the resistors, the

attenuation through the L-pad is lowered,

causing signal stretch. The amount of

stretch is determined by the adjustment

of R13. The signal is next applied to the

amplifier U2 that compensates for any

loss through the L-pad. The breakpoint,

or cut-in point, for the first corrector

stage is set by controlling where CR4 and

CR5 turn on. This is accomplished by

adjusting the cut-in resistor R34, which

forms a voltage-divider network from

+6.8 VDC to ground. The voltage at the

wiper arm of R34 is buffered by the

unity-gain amplifier U5D. This reference

voltage output of U5D is then applied to

R35, R36, and C39 through L12 to the

CR4 diode. C39 keeps the reference

from sagging during the vertical interval.

The .9 VDC reference created by CR11

and CR12 is applied to the unity-gain

amplifier U5B. The reference voltage is

then connected to the diode CR5 through

the choke L11. The two chokes L11 and

L12 form a high impedance for IF that

serves to isolate the op-amp ICs from the

IF.

After the signal is amplified by U2, it is

applied to the second corrector stage

through T2. The second and the third

corrector stages operate in the same

fashion as the first. All three corrector

stages are independent and do not

interact with each other.

The corrector stages are disabled by

moving the jumper W1 on J4 to the

Disable position, which is between pins 2

and 3. This moves all of the breakpoints

of the stages past the tip of sync so that

if adjusted they will have no affect on the

IF signal.

The IF signal exits the board at the IF

output jack J3 (0 dBm) after passing

through the three corrector stages. A

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-13

sample of the corrected IF is provided at

TP2. The IF output is normally connected

to an external IF phase corrector board.

4.1.5.10 Main IF Signal Path (Part 3 of 3)

After the IF signal passes through the

external IF phase corrector board, it

returns to the ALC board at IF input jack

J7 (0 dBm). The IF then passes through

a bandpass filter consisting of L20, C97,

C62, L21, L22, L23, C64, C99, and C63,

which is adjustable for best response.

This bandpass filter is intended to make

up for small errors in frequency response

that are incurred by the signal while

being processed through the linearity and

incidental phase correction circuits.

Following the bandpass filter, the signal

is split using L24, L25, and R89. The

signal passing through L24 is the main IF

path through the board. A sample of the

corrected main IF signal is split off and

connected to J10, the IF sample jack.

The main IF, whose level is controlled by

R99, connects to jacks J27 and J28.

These jacks control if a 6-dB pad is

included in the circuit by the positioning

of the jumpers W9 and W10. The 6-dB

pad is in when the jumpers W9 and W10

are connected between pins 2 and 3 on

J27 and J28. The 6-dB pad is out when

jumpers W9 and W10 are connected

between pins 1 and 2 on J27 and J28.

Normally, the pad is jumpered out. The

IF signal is then applied to a two-stage,

frequency-response corrector circuit that

is adjusted as needed. The variable

resistors R103 and R106 adjust the depth

and gain of the notches and the variable

capacitors C71 and C72 adjust the

frequency position of the notches. The

corrected IF signal is amplified by U13

and U14 before it is connected to J12,

the IF output jack of the board. The

output level is set for 0 dBm by R99.

The combined IF output of the ALC board

connects to (A11-A2) the filter/mixer

board. A sample of the IF is fed to J11 to

provide an IF sample point that can be

monitored without breaking the signal

path and gives an indication of the IF

signal after the linearity and the

frequency-response correction takes

place.

4.1.5.11 ALC Circuit

The other path of the corrected IF signal

is used in the ALC circuit. The IF is wired

out of the splitter through L25 and

connects to op-amp U12. The output of

U12 is wired to jacks J8 and J9 on which

jumpers W4 and W8 control the normal

or encoded operation of the ALC circuitry.

For normal operation, jumper W4 on J8

and jumper W8 on J9 are between pins 1

and 2. The IF signal is applied to the

transformer T5 that doubles the voltage

swing by means of a 1:4 impedance

transformation. The IF is then connected

to the ALC detector circuit on the board,

amplified by U10B and applied to jacks

J26 and J21.

For normal operation, jumper W7 on J26

and jumper W5 on J21 are between pins

1 and 2. The detected ALC voltage is

wired to U10A pin 2, where it is summed

with the front panel power control

setting. The output power adjustment

for the transmitter is controlled by the

screwdriver adjust pot R1, located on the

front panel of the VHF exciter tray. If the

(Optional) remote power raise/lower kit

is purchased, the power is set by

adjusting R75, a motor-driven pot

controlled by the switch S1 on the board.

An external power raise/lower switch can

be used by connecting it to jack J10, at

J10-11 power raise, J10-13 power

raise/lower return, and J10-12 power

lower, on the rear of the VHF exciter

tray. S1, or the remote switch, controls

relays K1 and K2, which control the

motor M1 that moves variable resistor

R75. If the (optional) remote power

raise/lower kit is not purchased, the ALC

voltage is controlled only by screwdriver

adjust pot R1 on the front panel of the

VHF exciter tray. The ALC voltage is set

for .8 VDC at TP4 with a 0 dBm output at

J12 of the board. A sample of the ALC at

J19 pin 2, is wired to the transmitter

control board where it is used on the

front panel meter and in the AGC circuits.

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-14

This ALC voltage, and the DC level

corresponding to the IF level after signal

correction, are fed to U10A pin 2, whose

output at pin 1 connects to the ALC pin-

diode attenuator circuit, CR1-CR3. If

there is a loss of gain somewhere in an IF

circuit, the output power of the

transmitter will drop and the ALC circuit

will sense this drop at U10A that will

automatically lower the loss of the pin-

diode attenuator circuit that increases

the IF level through the attenuator

circuit.

The ALC action starts with the ALC

detector level that is monitored at TP4.

The detector output at TP4 is nominally

+.8 VDC and is applied through the

resistor R77 to a summing point at the

op-amp U10A pin 2. The current

available from the ALC detector is offset,

or complemented, by the current taken

away from the summing junction. In

normal operation, U10A pin 2, is at 0

VDC when the loop is satisfied. If the

recovered or peak-detected IF signal at

the IF input jack J7 of this board should

drop in level, which normally means that

the output power is decreasing, the null

condition, 0 VDC, would no longer occur

at U10A pin 2. When the level drops, the

output of U10A at pin 1, will go more

positive. If jumper W3 on J6 is in the

Automatic position, it will cause the ALC

pin-diode attenuators CR1, CR2, and CR3

to have less attenuation therefore

increasing the IF level through them that

will act to compensate for the original

decrease in level. If the ALC cannot

increase the input level enough to satisfy

the ALC loop, due to not enough range,

an ALC fault will occur. The fault is

generated because U10D pin 12,

increases above the trip point set by R84

and R83 until it conducts. This makes

U10D pin 14, high and causes the red

ALC Fault LED DS2 to light.

4.1.5.12 (Optional) Scrambled Operation

with Encoding

For optional encoded, scrambled

operation, the jumper W4 on J8, the

jumper W8 on J9, the jumper W7 on J26

and the jumper W5 on J21 must all be

between pins 2 and 3. The IF is

connected through W4 on J8 to the sync

regeneration circuits beginning with L37.

If this board is operated with scrambling,

using suppressed sync, the ALC circuit

operates differently than described above

because there is no peak of sync present

on the IF input. A timing pulse from the

scrambling encoder must connect to the

board at J24. This timing pulse is

converted to sync pulses by U17A and

U17B, which control the operation of Q8.

The sync amplitude is controlled by R149

and is then applied to U15A, where it is

added to the detected IF signal to

produce a peak of sync level. The output

of U15A is peak detected by CR26 and

fed to U15B. If necessary, the

intercarrier notch L39 can be placed in

the circuit by placing the jumper W6 on

J22. The intercarrier notch is adjusted to

filter any aural and 4.5-MHz intercarrier

frequencies. The peak of sync signal is

fed through R162, the ALC calibration

control, to amplifier U15C. The amplified

peak of sync output is connected through

J21 pins 2 and 3, to U10A, where it is

used as the reference for the ALC circuit

and the AGC reference to the transmitter

control board. Voltage TP4 should be the

same in either the normal or the encoded

video mode. Monitor J9 pins 3 and 4,

with a spectrum analyzer, check that the

board is in the AGC mode, and tune C103

to notch-out the aural IF carrier.

4.1.5.13 Mute Fault Command

NOTE: This fault command circuit is not

used in the 334B VHF transmitter.

The ALC board has circuitry for an

external mute fault input that can

connect to J19 pin 6. This is a Mute

command, in most systems, it is involved

in the protection of the circuits of high

gain output amplifier devices. The Mute

command is intended to protect the

amplifier devices against VSWR faults. In

this case, the action should occur faster

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-15

than just pulling the ALC reference down.

Two different mechanisms are employed.

One is a very fast-acting circuit to

increase the attenuation of the pin-diode

attenuator, CR3, CR1, and CR2, and the

second is the reference voltage being

pulled away from the ALC amplifier

device. An external Mute is a pull-down

applied to J19 pin 6, to provide a current

path from the +12 VDC line through R78

and R139, the LED DS4 (Mute indicator),

and the LED section of opto-isolator U11.

These actions turn on the transistor

section of U11 that applies -12 VDC

through CR21 to U10A, pin 3, and pulls

down the reference voltage. This is a

fairly slow action that is kept at this pace

by the low-pass filter function of R81 and

C61. When the transistor section of U11

is on, -12 VDC is also connected through

CR22 to the pin-diode attenuator circuit.

This establishes a very fast muting

action, by reverse biasing CR3, in the

event of an external VSWR fault.

4.1.5.14 ±12 VDC Needed to Operate the

ALC Board

The ±12 VDC connects to the board at

J14. The +12 VDC connects to J14-3 and

is filtered by L30, L41, and C80 before it

is applied to the rest of the board. The

-12 VDC connects to J14-5 and is filtered

by L31 and C81 before it is applied to the

rest of the board.

One of the boards +12 VDC connects to

U16, a 5-VDC regulator IC that produces

the +5 VDC needed to operate the timing

IC U17.

4.1.6 (A9) IF Phase Corrector Board

(1227-1250; Appendix D)

The IF phase corrector board has

adjustments that pre-correct for any IF

phase modulation distortion that may

occur in the solid state amplifier devices

located in the external VHF amplifier

trays. Two separate, adjustable IF paths

are found on the board, a quadrature IF

path and an in-phase IF path. The

quadrature IF is 90° out of phase and

much larger in amplitude than the in-

phase IF. When they are combined in

Z2, it provides the required adjustable

phase correction to the IF signal.

The IF input signal (0 dBm) enters at J1

and is AC coupled to U1. U1 amplifies

the IF before it is connected to Z1, a

splitter that creates two equal IF outputs.

IF output 1 is connected to J2 and IF

output 2 is connected to J3. The IF

output 1, at J2, is jumpered through the

coaxial cable W4 to jack J6, the

quadrature input. The IF output 2, at J3,

is jumpered through the coaxial cable W5

to jack J7, the in-phase input.

4.1.6.1 Phase Corrector Circuit,

Quadrature Correction

The phase corrector circuit corrects for

any amplitude nonlinearities of the IF

signal. It is designed to work at IF and

has three stages of correction. Each

stage has a variable threshold and

magnitude control. The threshold control

determines the point at which the gain is

changed and the magnitude control

determines the gain change once the

breakpoint is reached. The second stage

has a jumper that determines the

direction of correction, so that the gain

can increased either above or below the

threshold, therefore either black or white

stretch can be achieved.

Two reference voltages are utilized in the

corrector stages and both are derived

from the +12 VDC line. Zener diode

VR1, with R46 as a dropping resistor,

provides +6.8 VDC. Diodes CR11 and

CR12 provide a .9 VDC reference, Vref, to

temperature compensate the corrector

circuits from the effects of the two diodes

in each corrector stage.

In the phase corrector circuit, the

Quadrature IF signal from J6 is applied to

the transformer T1, which doubles the

voltage swing using a 1:4 impedance

transformation. Resistors R8, R61, R9,

and R48 form an L-pad that attenuates

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-16

the signal. This attenuation is adjusted

by adding R7, a variable resistor, in

parallel with the L-pad. R7 is only in

parallel when the signal reaches a level

large enough to bias on CR1 and CR2

that allows current to flow through R7.

When R7 is put in parallel with the L-pad,

the attenuation through the L-pad is

lowered, causing black stretch.

The threshold for the first corrector stage

is set by controlling where CR1 and CR2

turn on. This is accomplished by

adjusting R3 that forms a voltage divider

from +6.8 VDC to ground. The voltage

at the wiper of R3 is buffered by U9C, a

unity-gain amplifier, and applied to CR1

through the choke L2. The .9 VDC

reference is connected to U9D, a unity-

gain amplifier, whose output is wired to

CR2 through the choke L3. The L2 and

L3 chokes form a high impedance for RF

to isolate the op-amps from any RF. The

adjusted signal is next applied to the

amplifier U2 that compensates for the

loss through the L-pad. U2 is powered

through L4 and R10 from the +12 VDC

line. After the signal is amplified by U2,

it is applied to the second corrector stage

through a matching, isolation

transformer T2 and then to a third

corrector stage through the matching,

isolation transformer T3. The other two

corrector stages operate in the same

manner as the first. Each stage is

independent and do not interact with

each other. The Quadrature corrected IF

output of the third corrector stage, at

unity gain through the three corrector

stages, is applied to pin 6 of the

combiner Z2.

When jumper W1 on J8 is connected

from pin 2 to pin 1, center to ground,

R15 is put in series with ground. In this

configuration, black stretch (white

compression) is applied to the IF signal

by controlling the attenuation through

the path. When W1 is connected from

the pin 2 to pin 3, center to the end that

connects to T2, R15 is put in parallel with

the L-pad. In this configuration, black

compression (white stretch) is applied to

the IF signal.

The phase correctors can be bypassed by

moving the jumper W2 on J9 to the

Disable position, between pins 2 and 3.

This action will move all of the threshold

points past sync tip so that they will have

no effect. R68 is adjusted and set for the

correction range that is needed. TP2 is a

test point that gives the operator a place

to measure the level of the quadrature IF

signal that is connected to pin 6 on

combiner Z2.

4.1.6.2 Amplitude Corrector Circuit, In

Phase Correction

The amplitude corrector circuit, in phase,

uses one stage of correction to correct

for any amplitude nonlinearities of the IF

signal. The stage has a variable

threshold control, R31, and a variable

magnitude control, R35. The threshold

control determines the point at which the

gain is changed and the magnitude

control determines the amount of gain

change once the breakpoint is reached.

Two reference voltages are needed for

the operation of the corrector circuit.

Zener diode VR1 with R46 provides the

+6.8 VDC reference. The diodes CR11

and CR12 provide the other reference of

.9 VDC, Vref, which temperature

compensates for the two diodes, CR8 and

CR9, in the corrector stage. In the

amplitude corrector circuit, the IF signal

from J7 is applied to transformer T4 to

double the voltage swing by means of a

1:4 impedance transformation. Resistors

R36, R55, R56, and R37 form an L-pad

that lowers the level of the signal. The

amount that the level is lowered is

adjusted by adding more, or less,

resistance, using R35 in parallel with the

L-pad resistors. R35 is only in parallel

when the signal reaches a level large

enough to turn on diodes CR8 and CR9.

When the diodes turn on, current flows

through R35 and puts it in parallel with

the L-pad. When R35 is in parallel with

the resistors, the attenuation through the

L-pad is lowered, causing signal stretch.

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334B, Rev. 0 4-17

The amount of stretch is determined by

the adjustment of R35.

The signal is next applied to the amplifier

U5 to compensate for the loss in level

through the L-pad. The breakpoint, or

cut-in point, for the corrector stage is set

by controlling where CR8 and CR9 turn

on. This is achieved by adjusting the

cut-in resistor R31 to form a voltage

divider from +6.8 VDC to ground. The

voltage at the wiper arm of R31 is

buffered by the unity-gain amplifier U8B.

This voltage is then applied to R34

through L11 to the CR9 diode. The .9

VDC reference created by CR11 and

CR12 is applied to the unity-gain

amplifier U8A. C36 keeps the reference

from sagging during the vertical interval.

The reference voltage is then connected

to the diode CR8 through choke L12.

The two chokes L11 and L12 form a high

impedance for RF to isolate the op-amp

ICs from the RF.

After the signal is amplified by U5, it is

applied to a second stage through T5.

The transformer doubles the voltage

swing by means of a 1:4 impedance

transformation. Resistors R39, R57,

R58, and R40 form an L-pad that delays

the signal to match the Quadrature input

path. The signal is then applied to

amplifier U6 that compensates for the

loss in level through the L-pad and

provides unity gain. After the signal is

amplified by U6, it is applied to a third

stage through T6. The transformer

doubles the voltage swing by means of a

1:4 impedance transformation. Resistors

R42, R59, R60, and R43 form an L-pad

that delays the signal to match the

Quadrature input path. The signal is

then applied to amplifier U7 to

compensate for the loss in level through

the L-pad. The in-phase corrected IF

signal is connected to pin 5 on the

combiner stage Z2. TP1 is a test point

that gives the operator a place to

measure the level of the in-phase IF

signal. The amplitude corrector can be

disabled by moving the jumper W3 on

J10 to the Disable position, between pins

2 and 3, which will move the breakpoint

past sync tip and the circuit will then

have no effect on the signal.

4.1.6.3 Output Combiner Circuit, Z2

The Quadrature, phase, corrected input

on pin 6 and the In phase, amplitude,

corrected input on pin 5 are combined in

Z2. The phase-corrected signal from pin

1 on combiner Z2 exits the board at the

IF output jack J4 after passing through a

pad network consisting of six resistors,

R62-R67, that provides a unity gain,

through the board, output level.

4.1.7 (A11) VHF Mixer/Amplifier

Enclosure Assembly, Low Band

(1070902; Appendix C)

The VHF mixer/amplifier enclosure

assembly is an aluminum enclosure that

provides RFI protection for the x2

multiplier board, the VHF filter/mixer

board, and the low-band VHF

filter/amplifier board, which are mounted

inside the enclosure.

4.1.7.1 (A1) x2 Multiplier Board

(1172-1111; Appendix D)

The x2 multiplier board multiplies the

frequency of the RF from the channel

oscillator by a factor of two. The board is

made up of a x2 broadband frequency

doubler.

The input signal, typically +5 dBm, at the

fundamental frequency enters through

the SMA jack J1 and is fed through a 3-

dB matching pad, consisting of R1, R2,

and R3, to the amplifier IC U1. The

output of the amplifier stage is directed

through a bandpass filter, consisting of

L1 and C4, that is tuned to the

fundamental frequency. The voltage

measured at TP1 is typically +0.6 VDC.

The RF is next connected to the doubler

stage that consists of Z1 and the

bandpass filter, L2 and C6, which is

tuned to the second harmonic. The

second harmonic is amplified by U2 and

fed to the SMA output jack of the board

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-18

at J2. The typical LO signal output level

is +5 dBm. The voltage measured at TP2

is typically +0.6 VDC.

The +12 VDC for the board enters

through jack J3-3 and is filtered by L3,

C2 and C7 before being distributed to the

rest of the board.

4.1.7.2 (A2) VHF Filter/Mixer Board

(1153-1101; Appendix D)

The VHF filter/mixer board is made up of

three separate circuits: a filter and

amplifier circuit for the LO input, a mixer

stage, and a filter and amplifier for the

RF output of the mixer.

The LO input, +5 dBm, from the x2

multiplier connects to the board at J3 and

is fed to a filter circuit. The input to the

filter consists of C11, C12, L5, and C12

that is adjusted for the best input

loading. C13 and C17 are adjusted for

the best frequency response and C18 is

adjusted for the best output loading of

the LO signal. The filtered LO is

amplified by U2 and connected to the LO

output jack J4, typically+14 dBm.

Normally, the output at jack J4 is

jumpered by a coaxial cable to jack J5 on

the board. The LO Input, +14 dBm, at

J5 connects to the mixer Z1 at pin 1.

The combined IF input, typically,

-3 to 0 dBm, from the ALC board,

connects to the board at J7 and is fed to

mixer Z1 at pin 3.

Mixer Z1 takes the LO input at pin 1 and

the IF input at pin 3 and produces an RF

output at pin 8. The RF output at pin 8

connects through a pi-type attenuator,

made up of R3, R4, and R5, before it is

connected to RF output jack J6, typically

-14 dBm in level. Normally, jack J6 is

connected by a coaxial cable to J1 on the

board. The RF from J1 is wired to the

input of a filter circuit, consisting of C25,

C1, C23, C2, and L1, with C2 adjusted

for the best input loading. C3 and C6 are

adjusted for the best frequency response,

C4 is adjusted for the best coupling, and

C7 is adjusted for the best output loading

of the RF signal. The filtered RF is

amplified by U1 and connected to the RF

output jack for the board at J2 (-2 dBm

to 0 dBm).

The +12 VDC needed for the operation of

the board is supplied by an external

power supply in the tray. The +12 VDC

enters the board at J8 pin 3, and is

filtered and isolated from the rest of the

tray by L7 and C22 before being applied

to the board.

4.1.7.3 (A3) Low Band VHF Filter/

Amplifier Board (1064251;

Appendix D)

The VHF low band filter/amplifier board is

made up of two separate circuits: a filter

circuit and an amplifier with a gain

control circuit.

The RF input connects to the board at J7,

typically 0 dBm, and is fed through a

channel filter circuit. The input filter

consists of C31, C27, C28, and C29, with

C29 adjusted for the best input loading.

C23 and C26 are adjusted for center

frequency, with C24 adjusted for the best

coupling, and C20 is adjusted for the best

output loading of the RF signal. The

filtered RF is connected to RF output jack

J6, which is usually jumpered to jack J1

on the board.

The filtered RF at J1 connects through a

7-dB pi-type attenuator, consisting of R1,

R2, and R3, before it is wired to a pin-

diode attenuator circuit. The pin-diode

attenuator circuit is made up of CR1,

CR2, and CR3 and is controlled by the

bias current applied to them through R5.

The diodes CR1, CR2, and CR3 are pin-

type diodes with a broad intrinsic region

sandwiched inside the diode. This broad

intrinsic region causes the pin diodes to

act as variable resistors instead of as

detecting devices at RF frequencies. The

resistance values of the pin diodes are

determined by the relative amount of

forward bias that is applied to the diodes.

Jumper W1 on J5 is set for manual gain

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334B, Rev. 0 4-19

or auto gain by its position on the jack.

Between 1 and 2 is manual gain, which

uses pot R9 to set the output level.

Between pins 2 and 3 is auto gain, which

uses an external control voltage input at

jack J4 as the level control. NOTE: The

334B transmitter operates in Manual

only.

The level set RF is pre-amplified by U1

and connected to Q1, the output

amplifier for the board. The RF output is

amplified by Q1 and connected to a

matching network with C17 adjusted to

maximize the RF signal level that is fed

to the direction coupler Z1. The RF exits

pin 4 of Z1 and connects to J2, the RF

output jack of the board (+10 dBm to

+20 dBm). Z1 provides a RF sample at

pin 3 that is split. The first split sample

connects to J8 through a voltage divider

consisting of R19 and R18 that is fed to

the front panel of the VHF exciter tray for

monitoring purposes. The second split

sample provided by Z1, pin 3, is fed

through a pad consisting of R20, R21,

and R22. The voltage is stepped up by a

1 to 4 transformer T1. The signal is then

peak detected by C32 and CR4 before

being buffered and amplified by U2A and

U2B. The peak-detected voltage at J9-1

and J9-2, which is used for metering

purposes, through the transmitter control

board, is level controlled by the pot R29

on the board.

The ±12 VDC needed for the operation of

the board is supplied by an external

power supply in the tray. The +12 VDC

enters the board at J3 pin 3, and is

filtered and isolated by L5 and C19

before being applied to the rest of the

board. The –12 VDC enters the board at

J3 pin 5, and is filtered and isolated by L6

and C35 before being applied to the rest

of the board.

4.1.8 (A17) Transmitter Control

Board (1265-1311; Appendix D)

The transmitter control board provides

system control functions and the

operational LED indications, which can be

viewed on the front panel of the

transmitter. The main control functions

are the Operate/Standby and

Auto/Manual selections. When the

transmitter is switched to Operate, the

board supplies the enables to the three

external VHF amplifier trays. The board

also performs the automatic switching of

the transmitter to Standby upon the loss

of the video input when the transmitter is

in Automatic.

The transmitter control board contains a

VSWR cutback circuit. If the VSWR of

the transmitter increases above 20%, the

VSWR cutback circuit will become active

and cut back the output level of the

transmitter, as needed, to maintain a

maximum of 20% VSWR.

An interlock (low) must be present at J8-

24 for the transmitter to be switched to

Operate. When the interlock is present,

the green Interlock LED DS5 will be lit.

4.1.8.1 Operate/Standby Switch S1

K1 is a magnetic latching relay that

controls the switching of the transmitter

from Operate and Standby. When the

Operate/Standby switch S1, on the front

panel of the tray, is moved to Operate,

the coil connected to pins 3 & 4 of relay

K1 energizes and causes the contacts to

close and apply a low to U4B-9. If the

transmitter interlock is present, and

there is no overtemperature fault, lows

will also be applied to U4B-10, 11, and

12. With all the inputs low to U4B, the

output at U4B-13 will also be low. This

low biases off Q1 that turns off the

amber Standby LED DS1 on the front

panel. Q1 off applies a high to Q2 that

turns on and lights the green Operate

LED DS2, also on the front panel. When

Q2 is biased on, it connects a low to Q12

that biases it off; which allows the ALC,

from J6 through U2C, to be applied to J1

and connect to the three external VHF

amplifier trays. The low from U4B-13 is

also applied to Q4 and Q24, which are

biased off that removes the disables from

J1-4, which connects to the remote

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334B, Rev. 0 4-20

standby indicator, if present, and J18-1.

The low from U4B-13 also connects to

Q10, which is biased on, and connects a

high to Q6, Q7, Q8, and Q9, which are

biased on and apply -12 VDC enables to

J8-2, J8-3, J8-4, and J8-5 that connect to

the VHF amplifier trays. The high applied

to Q2 is also connected to Q5, which is

biased on, and applies a low enable to

J1-3, which connects to the remote

operate indicator, if present, turning it

on. The transmitter is now in the

Operate mode.

When the Operate/Standby switch S1 is

moved to Standby, the coil connected to

pins 1 and 6, of relay K1 energizes,

causing the contacts to open and a high,

+12 VDC, to be applied to U4B-9. The

high at the input causes the output at

U4B-13 to go high. The high biases on

Q1, which applies a low to the amber

Standby LED DS1, on the front panel,

that turns on. The low is also applied to

Q2, which causes Q2 to turn off and

extinguishes the green Operate LED DS2.

The low from Q2 connects to Q12 that is

biased on, which causes the output from

U2C to go low that pulls the ALC voltages

at J1 low. This lowers the gain of the

external VHF amplifier trays. The high

from U4B-13 is applied to Q4 and Q24,

which are biased on, and applies a

disable at J1-4, which connects to the

remote standby indicator, if present, and

to J18-1, power supply disable, which is

not used in the 334B. The high from

U4B-13 connects to the base of Q10,

which is biased off. Q10 biased off

removes the high from Q6, Q7, Q8, and

Q9, which are biased off, and removes

the -12 VDC enables at J8-2, J8-3, J8-4,

and J8-5, which connect to the external

VHF amplifier trays, turning off the power

supplies in the trays. The low applied to

Q2 is also connected to Q5, which is

biased off, and removes the remote

enable at J1-3, which connects to the

remote operate indicator, if present,

turning it off. The transmitter is now in

the Standby mode.

4.1.8.2 Automatic/Manual Switch S2

K2 is a magnetic latching relay that

switches the operation of the transmitter

to Automatic or Manual using the

Auto/Manual switch S2 mounted on the

front panel of the VHF exciter tray.

When S2 is set to the Auto position, the

operation of the transmitter is controlled

by the fault circuits and will stay in

Operate even if the Operate/Standby

switch S1 is moved to Standby, as long

as no fault occurs. With S2 in Auto, a

low is applied to the coil connected to

pins 3 and 4, in the relay and this

energizes and closes the contacts. The

closed contacts apply a low to the green

Automatic LED DS3, which will light. The

low from the relay connects to U5A pin 2,

U5D pin 13, Q21, and Q23. The low to

Q21 and Q23 causes them to be biased

off, which causes their outputs to go

high. The high from Q21 connects to the

amber Manual LED DS4, on the front

panel, biasing it off, and also to Q22,

biasing it on. The drain of Q22 goes low

and is applied to J8-7 that enables any

remote auto indicator. The low to Q23

biases it off and removes the enable to

J8-6 and any remote manual indicator.

When S2 is set to the Manual position,

the operation of the transmitter is no

longer controlled by the fault circuits, it is

controlled by Operate/Standby switch S1.

With S2 in Manual, a low is applied to the

coil connected to pins 1 and 6 in the

relay that energizes and opens the

contacts. The open contacts remove the

low from the green Automatic LED DS3

on the front panel that causes it to not

light. The high connects to U5A pin 2,

U5D pin 13, Q21, and Q23. Q21 and 23

are biased on that causes their outputs to

go low. The low from Q21 connects to

the amber Manual LED DS4 on the front

panel, biasing it on, and to Q22, biasing

it off. The drain of Q22 goes high and is

applied to J8-7, which will disable any

remote auto indicators. Q23 is biased on

and applies a low to J8-6, which will

enable any remote manual indicators.

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-21

4.1.8.3 The Automatic Turning On and

Off of the Transmitter Using the Presence

of Video.

The transmitter control board also allows

the transmitter to be turned on and off

by the presence of video at the

transmitter when the transmitter is in

Auto. When a video fault occurs due to

the loss of video, J7-5 goes low. The low

is applied through the jumper W1, on

J10, to Q16, which is biased off, and to

the red Video Loss Fault LED DS9, on the

front panel, which will light. The drain of

Q16 goes high and connects to U5B pin

5, causing the output at pin 4 to go low.

The low connects to Q18, which is biased

off, and causes the drain of Q18 to go

high. The high connects to U3D pin 12,

whose output at pin 14 goes high. The

high connects to U5C pins 8 and 9,

causing its output at pin 10 to go low.

The high also connects U5A pin 1,

causing its output at pin 3 to go low.

With S2 set to Automatic, a low is applied

to U5A pin 2, and to U5D pin 13. When

U5A pin 1 is high and U5A pin 2 is low, it

causes the output at pin 3 to go low.

When U5D pin 12 is low and U5D pin 13

is low, it causes its output to go high.

When U5A pin 3 is low, it biases off Q20

and removes any pull down to the

Operate switch. A high at U5D pin 11,

biases on Q19 and applies a low enable

to the Standby switch that places the

transmitter in the Standby mode.

When the video signal is returned, J7-5

goes high. The high is applied to Q16,

which is biased on, and to the red Video

Fault LED DS9, which is extinguished.

The output of Q16 goes low and connects

to U5B pin 5. If there is no receiver ALC

fault, U5B pin 6, is also low, this causes

the output at pin 4 to go high. The high

connects to Q18, which is biased on, and

causes the drain of Q18 to go low. The

low connects to U3D pin 12, whose

output at pin 14 goes low. The low

connects to U5C pins 8 and 9, which

causes its output at pin 10 to go high.

The low also connects to U5A pin 1. With

the Auto/Manual switch S2 in Auto, a low

is applied to U5A pin 2, and to U5D pin

13. When U5A pins 1 and 2, are low, its

output at pin 3 goes high. When pin 12

of U5D is high, the output of U5D at pin

11 goes low. When U5A pin 3, is high, it

biases on Q20 and applies a pull-down

enable to the Operate switch. A low at

U5D pin 11, biases off Q19 and removes

any pull down to the Standby switch. As

a result of these actions, the transmitter

is switched to Operate.

4.1.8.4 Faults

There are four possible faults that may

occur in the transmitter and are applied

to the transmitter control board. They

are video loss fault, VSWR cutback fault,

overtemperature fault, and ALC fault.

During normal operation, no faults are

sent to the board. The receiver ALC fault

circuit will only function if a receiver tray

is part of the system. The

overtemperature fault is controlled by the

temperature of the heatsink of the

system 3 way combiner assembly.

4.1.8.5 Video Loss Fault

If a video loss occurs while the

transmitter is in Auto, the system will

switch to the Standby mode until the

video is returned. When this happens

the transmitter will immediately revert to

Operate. A video loss fault applies a low

from the ALC board to the video fault

input at J7-5 on the transmitter control

board. With jumper W1 in place on J10,

the video fault is connected to the LED

DS9 and to Q16. The red Video Loss

Fault LED DS9 on the front panel will

light. Q16 is biased off and causes its

drain to go high. The high is wired to

U5B pin 5, whose output at U5B pin 4

goes low. The low is wired to Q18, which

is biased off, and causes the drain to go

high. The high is connected to U3D pin

12, which causes its output at U3D pin

14 to go high. The high connects to U5A

pin 1. If the transmitter is in Auto, pin 2

of U5A is low. When pin 1 is high and pin

2 is low, the output of U5A goes low and

reverse biases Q20, shutting it off. The

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-22

high at U5C pins 8 and 9, causes its

output at pin 10 to go low. This low is

connected to U5D pin 12. If the

transmitter is in Auto, pin 13 of U5D is

also low. The lows on pins 12 and 13

cause the output of U5D to go high and

forward bias Q19. The drain of Q19 goes

low and energizes the coil connected to

pins 1 and 6 in relay K1, causing it to

switch to Standby.

When the video returns, the video loss

fault is removed from the video fault

input at J7-5. With jumper W1 in place

on J10, the base of Q16 goes high. The

red Video Loss Fault LED DS9 on the

front panel will be extinguished. Q16 is

biased on, which causes its drain to go

low. The low is wired to U5B pin 5. U5B

pin 6 will be low, if no ALC fault occurs.

The two lows at the inputs make the

output at U5B pin 4 go high. The high is

wired to Q18, which is biased on, causing

the drain to go low. The low is connected

to U3D pin 12, which causes its output at

U3D pin 14, to go low. The low connects

to U5A pin 1, and, if the transmitter is in

Auto, pin 2 of U5A is also low. With both

inputs low, the output of U5A at pin 3

goes high. The high forward biases Q20

and causes its drain to go low. The low

energizes to the operate coil connected

to pins 3 and 4 on relay K1 that switches

the transmitter to Operate. The low at

U5C pins 8 and 9, causes its output at

pin 10 to go high. This high is connected

to U5D pin 12, and, if the transmitter is

in Auto, pin 13 of U5D is low. The high

on pin 12 causes the output of U5D to go

low and reverse bias Q19. The drain of

Q19 goes high and this removes the low

from the standby coil in relay K1.

Transmitter is in Operate

4.1.8.6 Overtemperature Fault

In the 2-kW transmitter, the thermal

switch on (A8) the 3 way combiner

assembly connects to J8-1 on the board.

If the temperature of the heatsink on

which the thermal switch is mounted

rises above 175° F, the switch closes and

applies a low to J8-1. The low from J8-1

connects to the Overtemperature LED

DS6, which is biased on. The low also

connects to Q3, which is biased off,

causing the drain of Q3 to go high that

connects to pins 11 and 12 of U4B. The

high at the input to U4B causes it to go

high and switches the system to

Standby, which removes the Operate

Enable commands to the three external

VHF amplifier trays. After the thermal

switch cools below 175° F, the

transmitter will switch back to operate.

4.1.8.7 VSWR Cutback Fault

The reflected power sample of the RF

output of the transmitter, through the

visual/aural metering board, is connected

to J2 pin 9 of the transmitter control

board. The sample connects to op-amp

U1B pin 5, which buffers the signal

before it is split. One of the split

reflected samples connects to J1-5 on the

board that is wired to J10-5 on the rear

of the tray for remote monitoring.

Another split reflected sample connects

to position 3 on the front panel meter for

the tray. The final split remote reflected

sample connects to U2B pin 5. If this

reflected sample level increases above

the level set by R22, the VSWR cutback

pot, the output of U2B at pin 7, goes

high. The high is connected to Q11

through CR11, which is biased on,

making U2C pin 10, low and causing U2C

pin 8 to go low. This low is split and fed

out of the tray at J1-6, J1-7, J1-8, and

J1-9. These are AGC outputs to the VHF

amplifier trays that cut back the output

power of the amplifier trays. The low

from U2C pin 8, is also fed through

coaxial jumper W2 on J13 and J14 to

R73. R73 is a power adjust, bias-adjust,

pot that sets the level of the pin

attenuator bias available as an output at

J16. NOTE: This bias output is not used

in the 334B. The high at U2B pin 7, is

also fed to the base of Q14 and Q13,

which are forward biased. This produces

a low at the drains that connect to the

front panel amber VSWR Cutback LED

DS7, causing it to light and indicate that

the tray is in cutback, and to output jack

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-23

J8-37 for the connection to a remote

VSWR cutback indicator.

4.1.8.8 Receiver ALC Fault

If a receiver tray is part of the system, a

sample of the ALC voltage from this tray

is connected to J8-11 on the transmitter

control board. If the receiver is

operating normally, the ALC level that is

applied to U3C pin 9, remains below the

trip level set by R35; as a result, the

output at pin 13 stays high. The high is

applied to the red ALC Fault LED DS8,

which is off. The high also connects to

U3A pin 2, and to Q15. Q15 is biased on

and the drain goes low. The low

connects to U5B, pin 6. In addition, U5B

normally has a low that is connected to

U5B, pin 5, and produces a high at

output pin 4. The high is wired to Q18,

which is biased on, and makes its drain

low. The low connects to U3D pin 12,

which, because the level is below the

preset, the output at U3D pin 14 goes

low. A low at this point indicates a no-

fault condition. The high that is

connected to U3A pin 2, causes its output

to go low. The low is connected to Q25,

which is biased off. The low is removed

from J8-12, which will not light any

remote receiver fault indicator that is

connected to it.

If the receiver malfunctions, the ALC

level applied to U3C pin 9 goes high. This

is above the level set by R35 and causes

the output at pin 13 to go low. The low

is applied to the red ALC Fault LED DS8,

which lights. The low also connects to

U3A pin 2 and to Q15. Q15 is biased off

and the drain goes high. The high

connects to U5B pin 6 that produces a

low at output pin 4. The low is wired to

Q18, which is biased off and makes its

drain go high. The high connects to U3D

pin 12 and, because the level is above

the preset, the output at U3D pin 14

goes high. A high at this point indicates

a fault condition that switches the

transmitter to Standby. The low

connected to U3A pin 2, causes its output

to go high. The high is connected to

Q25, which is biased on and causes the

drain to go low. The low is connected to

J8-12, which can light any remote

receiver fault indicator that is connected

to it.

4.1.8.9 Metering

The front panel meter connects to J3-1

(-) and J3-2 (+), the output of switch S3,

on the transmitter control board. The

front panel meter has seven metering

positions, which are controlled by S3.

They are the Audio level, Video level, %

Aural Power, % Visual Power, %

Reflected Power, % Exciter Power, and

ALC level. A sample of the video

connects to the board at J5-4 and is

connected through the video calibration

pot R20 to position 6 on front panel

meter switch S3. An audio sample enters

the board at J5-6 and is connected

through audio calibration pot R19 to

position 7 on front panel meter switch

S3. A reflected sample connects to the

board at J2-9 and is connected through

buffer amplifier U1B and 100Ω resistor

R84 to position 3 on front panel meter

switch. A visual sample connects to the

board at J2-5 and is connected through

buffer amplifier U1D and 100Ω resistor

R86 to position 4 on the meter switch.

The aural sample connects to the board

at J2-7 and is connected through buffer

amplifier U1C and 100-watt resistor R85

to position 5 on the front panel meter

switch. An exciter sample connects to

the board at J2-3 and is connected

through the buffer amplifier U1A and the

100Ω resistor R87 to position 2 on the

front panel meter switch. An ALC sample

connects to the board at J6-1 and is

connected through the buffer amplifier

U2C and the ALC calibration pot R15,

which adjusts the output of U2A pin 1,

and through the 100Ω resistor R18 to

position 1 on front panel meter switch.

Typical readings on the meter are:

• Video = 1 Vpk-pk at white

• % Reflected = < 5%

• % Visual power = 100%

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-24

• % Aural power = 100%

• % Exciter = The level on the meter

needed to attain 100% output power

from the transmitter

• ALC = .8 VDC

• Audio = ±25 kHz with a balanced

audio input or ±75 kHz with a

composite audio input

Refer to the test data sheet for the

transmitter for the actual reading:

Remote metering samples are provided

at J1-10 for the exciter, J8-26 for the

visual, J8-27 for the aural, and J1-5 for

the reflected. U6 is a temperature

sensor IC that gives the operator the

ability to measure the temperature inside

the tray by measuring the voltage at

TP1. The sensor is set up for +10 mV

equals 1° F. (for example, 750 mV equals

75° F).

4.1.8.10 Operational Voltages

The +12 VDC needed for the operation of

the transmitter control board enters the

board at jack J4 pin 3. C28, L1, and L3

are for the filtering and isolation of the

+12 VDC before it is split and applied to

the rest of the board. The -12 VDC

needed for the operation of the board

enters the board at jack J4 pin 5. C29

and L2 are for the filtering and isolation

of the -12 VDC before it is split and

applied to the rest of the board.

Four +12 VDC outputs are fed out of the

board at J8-16, J8-17, J8-18, and J8-19

through diodes CR7, CR8, CR9, or CR10

and resistors R50, R51, R52, or R53 to

the three VHF amplifier trays for use in

their logic circuits. The resistors are for

current limiting and the diodes are to

prevent voltage feedback from the VHF

amplifier trays.

4.1.9 (A19) Visual/Aural Metering

Board (1265-1309; Appendix D)

The visual/aural metering board provides

detected outputs of the visual, aural, and

reflected output samples that are used

for monitoring on the front panel meter.

These readings are attained from

samples of the forward power and

reflected power outputs from (A16) the

output coupler assembly for the

transmitter. The board also provides

adjustments for the calibration of the

readings on the meter.

A forward power sample, visual + aural,

is applied to the SMA jack J1 on the

board. The input signal is split, with one

path connected to the front panel forward

power sample SMA jack J2 for monitoring

purposes. The other path is connected

through C1 to CR2, R4, R5, R6, C4, and

CR1, which make up a detector circuit.

The detected visual + aural signal is

amplified by U6B and its output is split.

One amplified output of U6B connects to

the aural level circuit and the other

output connects to the visual level circuit.

4.1.9.1 Aural Level Circuit

One of the detected visual + aural level

outputs of U6B connects through C6 to

the intercarrier filter circuit that consists

of R13, R14, L1, C7, and C8. C8 and L1

are typically adjusted for a maximum

aural reading. The filter notches out the

video + aural and only leaves the 4.5-

MHz difference frequency between the

visual and aural, which is a good

representation of the aural level. The

4.5-MHz signal is fed to the buffer

amplifier U6A. The output of U6A is

detected by the diode detector CR3 and

U1A and then fed through the aural

calibration control R20 to amplifier U2D.

The amplified output of U2D is split, with

the main output connected through R21

to J6 pin 1, which supplies the aural level

output to the front panel meter for

monitoring. The other output of U2D is

connected to the aural null adjust R51

and offset null adjust R48, which are

adjusted to set up the visual power

calibration output.

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-25

4.1.9.2 Visual Level Circuit

The other detected visual + aural level

output from U6B is connected to U1C

and, if there is no scrambling, connects

directly to intercarrier notch L3, which is

adjusted to filter out the aural and the

4.5-MHz intercarrier frequencies, leaving

only a visual + sync output. The visual +

sync output is fed to a peak detector

circuit consisting of CR5 and U2A. The

signal is then fed through the visual

calibration control R28, which is adjusted

for a 100% visual reading with no aural,

to amplifier U2B. The amplified visual

peak of sync output is connected to

comparator U2C. The other input to U2C

is the level set by the aural null adjust

R51, which is adjusted for 100% visual

power after the aural is added and the

peak power is adjusted back to the

reference level and also from the offset

null adjust R48, which is adjusted for 0%

visual power with the transmitter in

Standby. The adjusted output is

amplified by U3D and connected to the

other input of U2C pin 9. The output of

U2C connects to J6 pins 2 and 3, which

supply the peak of sync visual level

output to the front panel meter for

monitoring.

If this board is operated with scrambling,

using suppressed sync, the visual level

circuit operates differently than described

above because there is no peak of sync

present on the forward sample input. For

the board to operate properly, a timing

pulse from the scrambling encoder must

connect to the board at J4. This timing

pulse is converted to sync pulses by U4A

and U4B, which control the operation of

Q2. Intercarrier notch L2 is tuned to

remove any visual + aural signal that

may remain. The sync amplitude is

controlled by the gate amplitude adjust

R25 and then applied to the minus input

of U1C. At this point, the sync is inserted

into the visual + aural signal that is

connected to the plus input of U1C,

producing a peak of sync in the signal.

The output of U1C is connected to

intercarrier notch L3, which is adjusted to

filter out the aural and the 4.5-MHz

intercarrier frequencies. The visual +

sync output is fed to a peak detector

circuit, consisting of CR5 and U2A, and

then fed through the visual calibration

control R28 to amplifier U2B. The

amplified visual peak of sync output is

connected to J6 pins 2 and 3, which

supply the peak of sync visual level

output to the front panel meter for

monitoring. R32 moves the pulse to

where the sync should be and R25 sets

the visual metering calibration with no

sync present.

4.1.9.3 Reflected Level Circuit

A reflected-power sample is applied to J3

of the visual/aural metering board and is

detected by the diode detector circuit

CR7 and U3B. The detected output is fed

through the reflected calibration pot R39,

which can be adjusted to control the gain

of U3C. The output of U3C connects to

J6 pin 7, which supplies a reflected power

level output to the transmitter control

board for VSWR cutback and also to the

front panel meter.

4.1.9.4 Voltages for Circuit Operation

The ±12 VDC is applied to the board at

J5. The +12 VDC is connected to J5 pin

3, and is isolated and filtered by L4 and

C34 before it is connected to the rest of

the board. One +12 VDC line connects

to U5, a 5-VDC regulator that provides

the voltage needed to operate U4. The

-12 VDC is applied to J5 pin 5, and is

isolated and filtered by L5 and C35

before it is connected to the rest of the

board.

4.1.10 (A14) Channel Oscillator

Assembly, Dual Oven (1145-1202;

Appendix D)

NOTE: If the precise frequency kit is

present in your transmitter, the VCXO

Assembly (1145-1206) will be used.

The channel oscillator assembly contains

(A14-A1) the channel oscillator board

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-26

(1145-1201) that generates a stable

frequency reference signal of

approximately 100 MHz. The channel

oscillator assembly is an enclosure that

provides temperature stability for the

crystal oscillator. An SMA output at jack

J1 and an RF sample at BNC connector

jack J2 are also part of the assembly.

Adjustments can be made through access

holes in the top cover of the assembly.

These adjustments are set at the factory

and should not be tampered with unless

it is absolutely necessary and the proper,

calibrated equipment is available. R1 is

the temperature adjustment; C11 is the

course-frequency adjustment; C9 is the

fine-frequency adjustment; and C6, C18,

L2, and L4 are adjusted for the maximum

output level at the frequency as

measured at jack J1.

The +12 VDC for the assembly enters

through FL1 and the circuit ground

connection is made at E1.

4.1.10.1 (A14) (Optional) VCXO

Assembly, Dual Oven (1145-1206;

Appendix D)

NOTE: If the precise frequency kit is not

present in your transmitter, the Channel

Oscillator Assembly (1145-1202) will be

used.

The VCXO assembly contains the VCXO

channel oscillator board (1145-1204),

which generates a stable frequency

reference signal of approximately 100

MHz. The VCXO channel oscillator

assembly is an enclosure that provides

temperature stability for the crystal

oscillator. An SMA output at jack J1

feeds the x2 multiplier board and an RF

sample at BNC connector jack J2

provides an oscillator sample to the front

panel of the VHF exciter tray.

Adjustments are provided through access

holes in the top cover of the assembly.

These adjustments are set at the factory

and should not be adjusted unless it is

absolutely necessary and the properly

calibrated equipment is available. R1 is

the temperature adjustment; C11 is the

course frequency adjustment; and C6,

C18, L2, and L4 are adjusted for

maximum output level at frequency as

measured at jacks J1 or J2. The AFC

voltage, which is fed to FL2 from the

precise frequency control tray, is the fine

frequency adjustment.

The +12 VDC for the assembly enters

through FL1 and the circuit ground

connection is made at E1.

4.1.11 (Optional) (A13) EEPROM FSK

Identifier Board (1265-1308;

Appendix D)

The (Optional) FSK identifier board, with

EEPROM, generates a morse code

identification call sign by sending a bias

voltage to the IF attenuator board to

amplitude modulate the aural carrier.

This gives the station a means of

automatically repeating its identification

call sign, at a given time interval, to

meet FCC requirements.

The starting circuit is made up of U1B

and U1D, which are connected as a

flip-flop, with gate U1A used as the set

flip-flop. U1A automatically starts the

flip-flop each time U3 completes its

timing cycle. At the start of a cycle, U1B

enables clock U2. U2 applies the clock

pulses that set the speed, which is

adjusted by R2, for when the

identification code is sent to 12-bit binary

counter U4. R2, fully clockwise (CW), is

the fastest pulse train and R2, fully

counter-clockwise (CCW), is the slowest

pulse train. U4 provides binary outputs

that address EEPROM U5.

The scans in U4 will continue until the

field effect transistor (FET) Q1 is gated

on. The gate of Q1 is connected to pin

13 on U4, which is the maximum count

used in the EEPROM, and will provide a

reset pulse each time the binary counter

goes high on pin 13. The reset pulse,

when the drain of Q1 goes low, is applied

to the flip-flop and the timer U3, which

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-27

determines the length of time between

the sending of the identification code.

R14 is adjusted to set this time interval.

R14, fully CW, is the longest interval

between identification calls,

approximately eight minutes. R14, fully

CCW, is the shortest interval between the

sending of the code (approximately 10

seconds).

U6B is an amplifier connected to the

output of U5, which turns the LED DS1

on and off at the rate set by R2. This

gives the operator a visual indication that

the FSK identifier board is operating and

at the rate at which it is operating.

The data output of U5, which is serial, is

connected to U6A, whose output shifts

low and high, and is applied to the VCXO

board, which shifts the frequency

according to the programming of U5. The

deviation of the shift is adjusted by R4

and is typically set at 1 kHz. Once R4 is

set, R9 is re-adjusted to -1.5 VDC at J3-

The +12 VDC from an external power

supply enters the board at J1, pin 3. The

voltage is fed through RF choke L1 and is

filtered by C1 before being applied to the

rest of the tray. The +12 VDC is also

applied to U7, which is a voltage

regulator that regulates its output at +5

VDC. The +5 VDC is fed to the ICs on the

board. The -12 VDC from an external

power supply enters the board at J1, pin

5. The voltage is fed through RF choke L2

and filtered by C2 before being applied to

the rest of the tray.

4.1.12 (Optional) (A12) IF

Attenuator Board (1150-1201;

Appendix D)

The IF attenuator board is operated with

the FSK identifier board to produce an

amplitude modulated aural IF signal for

broadcasting the required FCC station

identification call sign at the proper time

intervals. The board contains a pin-diode

attenuation circuit that consists of CR1

and the two resistors R2 and R3. The

bias output of the FSK identifier board is

applied to J3 of the IF attenuator board.

As the bias applied to J3 increases and

decreases, the amplitude of the aural IF

signal, which enters the board at J1 and

exits the board at J2, will increase and

decrease. This produces an amplitude-

modulated IF signal at J2, the aural IF

output jack of the board.

4.2 (A6, A7 and A11) Low Band VHF

Amplifier Trays (1304363;

Appendix C)

The low band VHF amplifier tray is

adjusted at the factory for use as a visual

+ aural RF amplifier tray. The tray has

approximately 55 dB of gain at the

frequency of the VHF low band channel

and will take the typical +7 dBm Visual

– 3dBm Aural input and amplify it to an

output level of approximately +58.8

dBm. As a visual + aural amplifier, the

tray is calibrated for 750 watts peak of

sync visual plus 10 dB aural power (75

watts) that is equal to a 100% meter

reading.

The tray is made up of the boards and

assemblies listed in Table 4-1.

Table 4-1. VHF Amplifier Tray Boards and Assemblies

MAJOR ASSEMBLY

DESIGNATOR BOARD/ASSEMBLY NAME DRAWING NUMBER

A2-A1 Phase shifter board (mounted in

[A2] an RF enclosure assembly) 1198-1602

A2-A2 Filter/amplifier board (mounted in

[A2] an RF enclosure assembly) 1198-1606

A3-A1 Low band VHF amplifier board

(mounted in [A3] an RF enclosure

1198-1605

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-28

assembly)

MAJOR ASSEMBLY

DESIGNATOR BOARD/ASSEMBLY NAME DRAWING NUMBER

A3-A2 Overdrive protection board

(mounted in [A3] an RF enclosure

assembly) 1198-1601

A3-A3 3-way splitter board (mounted in

[A3] an RF enclosure assembly) 1198-1608

A4-A1, A4-A2 and A4-A3 Three low band VHF amplifier pallets

(mounted in [A4] an RF enclosure

assembly)

P400-VHF-L-18

1304348

A5-A1 3-way combiner board (mounted on

[A5] the combiner heatsink

assembly) 1198-1626

A13 AGC control board 1142-1601

A8 Current metering board 1304362

A10 +30 VDC switching power supply

assembly PM3329B-5-1-R-2-E

1301504

The on-channel RF input signal (+7 dBm

Visual –3 dBm Aural) enters the rear of

the tray at the BNC jack J1 and is fed

through J1 of the (A2) enclosure

assembly to J1 of (A2-A1) the phase

shifter board (1198-1602). The board

provides a phase shifter adjustment of

the RF signal that is needed to provide

maximum output during the combining of

the three VHF amplifier trays in the 3

way combiner. The front panel mounted

phase shift potentiometer R2 (A7)

connects to J3 on the board and controls

the phase of the RF signal.

If the input signal level to the phase

shifter board falls below a preset level, a

high, which is an input fault, connects

from J5 of the board to J14 on the AGC

control board. When an input fault

occurs, the AGC control board generates

a fault output at J1, which is connected

to J4 on the filter/amplifier board. The

fault cuts back the RF signal level using

the pin-diode attenuator circuit on the

filter/amplifier board.

The phase-controlled output at J2 of the

phase shifter board (+7 dBm) is directed

to J7, the input jack of the (A2—A2) filter

amplifier board (1198-1606) that is made

up of two circuits. The first circuit is a

channel filter that is adjusted for the

desired channel frequency and

bandwidth. The filtered output (+5 dBm)

is connected to the second circuit that

contains two amplifiers. The RF connects

through a pin-diode circuit to the

amplifier IC U1. The voltage applied to

J4, which is the external control jack of

the board, controls the amplitude of the

RF signal through the pin-diode

attenuator circuit. Jumper W1 on J5

should be between pins 2 and 3, which

provide external control, through J4, of

the gain of the board, as well as the

output level of the tray. R9 is the

manual gain pot that is in the circuit

when the jumper W1 is between pins 1 &

The front panel mounted gain pot R3

(A6) connects to the AGC control board

and is used to adjust the AGC pin-

attenuator bias voltage that connects to

J4 on the filter/amplifier board. The RF

signal, after the pin-attenuator circuit, is

amplified by the second amplifier stage

Q1 to about +19.5 dBm; this signal is

connected to the output of the board at

J2.

The RF output of the filter/amplifier

board connects to J2 of (A3) a RF

enclosure that contains the low band VHF

amplifier board, the overdrive protection

board and the 3-way splitter board. The

RF from J2 on the enclosure connects to

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-29

J1 on the low band VHF amplifier board

(1198-1605) that amplifies the signal

approximately 22 dB.

The RF output of the low band VHF

amplifier board at J2 (+41.5 dBm)

connects to J4 of (A3-A2) the overdrive

protection board (1198-1601). The RF

signal is through connected directly to J5,

the RF output jack of the board. A

sample of the RF on the board is applied

to a diode-detector circuit that consists of

CR1 and U1A. The gain of amplifier U1D

is controlled by detector gain pot R11,

which is set to +.4 VDC as measured at

TP1. The set output of U1D is connected

to the comparator IC U1B. The trip point

for the comparator is adjusted by R12,

typically set to 110% output power, sync

only. When the signal reaches that level,

the overdrive protection board will cut

back the output power of the tray and

the red Overdrive LED DS1 located on

the board and the red Overdrive LED DS1

mounted on the front panel will be

illuminated. Typically, the output power

level will bounce down and then up and

continue bouncing until the output level

is lowered to the normal operating level

(100%). The red Overdrive LED DS1,

the green Module LED DS3, and the

Enable LED DS2 may blink on and off

during the bouncing of the output level;

this is a normal occurrence. The greater

the output level is above 110%, the

larger the bounce will be.

The RF output of the overdrive protection

board at J5 connects to J1 on (A3-A3)

the 3-way splitter board (1198-1608).

The splitter board takes the +41.3 dBm

input and provides three +36.3 dBm

outputs at J1, J2 and J3 of the (A3)

amplifier enclosure.

The three RF outputs connect to (A4) the

final amplifier enclosure. This enclosure

contains three (A4-A1, A4-A2 and A4-A3)

low-band amplifier pallets 1304348

(P400-VHF-L). The RF signals connect to

J1 on each of the low-band amplifier

pallets. Each amplifier pallet provides

approximately 18 dB of gain.

The RF signal inputs to the amplifier

pallets (+36.3 dBm) are amplified to

+54.3 dBm outputs at J2. These outputs

are connected to J1, J2 and J3 on (A5-

A1) a 3-way combiner board (1198-

1626). The 3-way combiner takes the

three +54.3 dBm inputs and combines

them to form the 750-watt RF output at

J5 of the combiner that connects to J2,

the RF output jack of the tray.

The (A5-A1) 3-way combiner board

provides a forward power sample at J6

and a reflected output power sample at

J7. The forward output power sample

connects to J4 on (A13) the AGC control

board (1142-1601). The reflected output

power sample connects to J5 on (A13)

the AGC control board (1142-1601). The

AGC control board contains two peak-

detector networks that provide detected

outputs that are used for front panel and

remote meter indications of forward and

reflected output power levels, the AGC

detector voltage level, and the VSWR

cutback protection if the reflected power

level increases above the preset level.

+30VDC and +12 VDC Voltages

Two voltages, +30 VDC from the internal

switching power supply and +12 VDC

from the VHF exciter tray, are needed for

the operation of the tray. The +12 VDC

connects to J3-7 and J3-8 on the rear of

the tray and are wired to J8 pins 4 and 1,

on (A13) the AGC control board. The

+12 VDC is connected to U8, a +5 VDC

regulator IC that supplies the +5 VDC

needed for the operation of the front

panel mounted LEDs.

The (A10) +30 VDC switching power

supply provides the +30 VDC to (A8) the

current metering board (1304362). The

current metering board distributes the

+30 VDC through fuses to the amplifier

devices on (A2-A2) the filter/amplifier

board, (A3-A1) the low-band amplifier

board, and A4-A1, A2 & A3) the three

final low-band amplifier pallets. +12

VDC from the AGC control board is

through connected to the (A2-A1) phase

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-30

shifter board, the (A2-A2) filter/amplifier

board and the (A3-A2) overdrive

protection board.

The fuses F1, F2 and F3 are 20-amp

fuses. F4 is a 5-amp fuse, F6 is a 2-amp

fuse, and F7 is a 1-amp fuse. F5 is not

used in this configuration. The 20 amp

fuse F1 protects +30 VDC to (A4-A1) one

of the low-band final amplifier pallet, the

20 amp fuse F2 protects (A4-A2) another

low-band final amplifier pallet and the 20

amp fuse F3 protects (A4-A3) the last

low-band final amplifier pallet. The 5

amp fuse F4 protects +30 VDC to (A3-

A1) the low-band VHF amplifier board.

The fuse F5 is not used in this

configuration. The 2 amp fuse F6

protects +30 VDC to (A2-A2) the

filter/amplifier board. The 1 amp Fuse F7

protects the +30 VDC connected to J8

pin 2, on (A13) the AGC control board.

On the AGC control board, the +30 VDC

is connected to the regulator IC U7 that

takes the +30 VDC and regulates it to a

+12 VDC output. The +12 VDC is used

for the operation of the AGC control

board. The +12 VDC from A13-J11-3 is

connected to the current metering board

at A8-TB1-5. The +12 VDC is jumpered

on TB1 from TB1-5 to TB1-6, which is

wired to the (A2-A1) phase shifter board,

the (A2-A2) filter/amplifier board, and

the (A3-A2) overdrive protection board.

The current metering board also supplies

sample outputs of the operating currents

of the amplifier devices in the tray to the

front panel current meter. The meter in

the (I1) position reads the current for the

(A4-A1) low-band final amplifier pallet,

the meter in the (I2) position reads the

current for (A4-A2) the low-band final

amplifier pallet and the meter in the (I3)

position reads the current for the (A4-A3)

low-band final amplifier pallet. The

meter in the (ID) position reads the

current for the (A3-A1) low-band VHF

amplifier board. To read the desired

current, place switch S1 to the Current

position, then place switch S2 to the

desired current measuring position.

These current readings can be used when

setting up the idling currents, no RF drive

applied, for the devices. The (I1, I2, and

I3) currents are each set for 1.8 amps,

while the (ID) current is set for 3 amps.

220 VAC Input

In the tray, the 220 VAC is applied

through jack J4 to terminal block TB1.

When CB1, the 15-amp, front panel-

mounted circuit breaker, is switched on,

the 220 VAC is distributed from TB1 to

(A11 and A12) two cooling fans, which

will begin to operate, and to (A10) the

switching power supply. There are four

surge suppressors on the AC input lines

for protection from transients or surges.

VR1 and VR2 are mounted on TB1,

between the AC lines and VR3 and VR4

are mounted at the input to the switching

power supply from each AC line to

ground.

Power Supply Enable

The (A10) switching power supply only

operates when the power supply enable

control line, jack J3 pins 9 and 10, on the

rear of the tray, is shorted and there is

no overtemperature fault. The enable is

supplied by the VHF exciter tray when

the transmitter is switched to Operate.

The enable is applied to J10 pins 10 and

9 on (A13) the AGC control board (1142-

1601), which, if there is no

overtemperature fault, connects the

enable from J10 pins 6 and 7 to J1-18

and J1-14 located on the switching power

supply assembly. The green Enable LED

DS2 on the front panel will light,

indicating that an enable is present. If

the transmitter is in Standby, or if an

overtemperature fault occurs, the AGC

control board will not enable the

switching power supply. As a result, the

+30 VDC will be removed from the

amplifier modules and the front panel

Enable and Module Status LEDs will not

be lit.

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-31

Front Panel Metering

The front panel meter (A9) uses the front

panel Selector switch S1 to monitor the

AGC Voltage, % Forward Power, %

Reflected Power, the power supply

voltage, and the current. The meter in

the AGC position will read between 1 and

2 volts. The power supply voltage

reading is calibrated using R86 on the

AGC control board. The % Output Power

is calibrated using R44 and the %

Reflected Power is calibrated using R53

on the AGC control board. With S1 in the

Current position, S2 can be switched to

read the idling currents, no RF drive

applied, of the low-band amplifier pallets.

Typical readings are an idling current of

1.8 amps in the I1, I2, and I3, positions

and 3 amps in the ID position.

Reflected Power Sample

The reflected power sample from the 3-

way combiner board is fed back to the

AGC control board at J5. On the board,

the reflected sample is connected

through a detector circuit, CR13 and

associated components, to the VSWR

cutback circuit, consisting of U5B and

associated components. If the reflected

power increases above 20%, the output

power of the tray, as set by R59, the

VSWR cutback adjust, will be cut back to

maintain a 20% reflected output level.

The red VSWR Cutback LED DS4 on the

front panel will remain lit until the

reflected level drops below 20%.

Thermal Protection Devices

There are three thermal switches in the

tray for overtemperature protection.

Two of the thermal switches (A4-A6 and

A4-A5) are mounted to the (A4) heatsink

for the three low-band amplifier pallets

and the third thermal switch (A5-A2) is

mounted on the (A5) heatsink for (A5-

A1) 3-way combiner board. The thermal

switches close when the heatsink on

which they are mounted reaches a

temperature of 175° F. The closed

thermal switch causes the AGC control

board to remove the enable to the

switching power supply. This eliminates

the +30 VDC and lights the red

Overtemperature LED DS5 on the front

panel and the AGC control board will

extinguish the green Module Status LED

DS3.

4.3 (A8) 3 Way Combiner Assembly

(1065241; Appendix D)

The outputs of the three VHF amplifier

trays (750 Watts each) connect to the 3

way combiner assembly. They are

combined to give approximately 2200

Watts at J5 of the assembly. A thermal

switch is mounted to the heatsink of the

combiner for overtemperature protection

in case of amplifier failure or a problem in

the output filtering network. The thermal

switch closes when the heatsink on which

it is mounted reaches a temperature of

175° F. The closed switch connects an

overtemperature command through FL1

& FL2 on the combiner to J11-1 & J11-35

on the VHF Exciter. The

overtemperature command will cause an

overtemperature fault, that will remove

the enables to the VHF amplifier trays

and place the transmitter in Standby.

4.4 (A13) Harmonic Filter, (A14)

Bandpass Filter and (A16) Coupler

Assembly

The RF output of the 3 way combiner at

(A8-J5) is fed through 1/2" superflex to a

7/8” to 1-5/8” adapter that connects to

J1 on the (A13) harmonic filter. The

harmonic and bandpass filters screen out

the -3.58-MHz, -4.5-MHz, +8.08-MHz,

+9.00-MHz intermodulation products, as

well as all of the visual and aural

harmonic frequencies. The output of the

(A14) bandpass filter is fed through 1-

5/8” hardline to (A16) the output

coupler. The coupler provides a reflected

and a forward power sample to the VHF

exciter for VSWR and metering purposes.

The forward sample connects to J8 and

the reflected sample connects to J9 on

the VHF exciter tray. The output of the

coupler, 2000 watts, at the 1-5/8”

2000-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions

334B, Rev. 0 4-32

connector J2 is then fed to the antenna

for your system.

This completes the description of the

334B VHF Low Band Transmitter.

2000-Watt VHF Low Band Transmitter Chapter 5, Detailed Alignment Procedures

334B, Rev. 0 5-1

Chapter 5

Detailed Alignment Procedures

The 334B transmitter was aligned at the

factory and should not require additional

alignments to achieve normal operation.

This transmitter operates using the

baseband audio and video inputs or, if

the (optional) 4.5-MHz composite input

kit is purchased, either a single

composite video + 4.5-MHz input or

separate baseband video and audio

inputs.

Check that the RF output at J2 of (A16)

the coupler is terminated into a dummy

load of at least 2000 watts. While

performing the alignment, refer to the

Test Data Sheet for the transmitter and

compare the final readings from the

factory with the readings on each of the

trays. They should be very similar. If a

reading is off by a significant amount, the

problem is likely to be in that tray.

Switch on the main AC circuit breaker for

the transmitter and the VHF exciter

circuit breaker located on the rear of the

tray.

5.1 (A4) VHF Low-Band Exciter Tray

(1070820 or 1304463 w/P.F;

Appendix C) with Baseband Video

and Audio Inputs

NOTE: The 1304463 VHF Exciter is used

with the precise frequency system and

will contain the VCXO Assembly (1145-

1206), in place of the Channel Oscillator

Assembly (1145-1202), and the IF VCXO

Board (1248-1131), in place of the IF

Oven Oscillator Assembly (1191-1404).

The (A4) low-band VHF exciter tray has

adjustments for video levels, audio

modulation levels, and other related

parameters.

Connect an NTSC baseband video test

signal input (1 Vpk-pk) to the transmitter

video input jack J2 on the (A12) remote

interface panel. Jacks J1 and J2 on the

VHF exciter tray are loop-through

connected and the unused jack J2 can be

used as a video source for another

transmitter by removing jumper W4 on

jack J3 on (A5) the sync tip clamp

modulator board (1265-1302). Connect

a baseband audio input (+10 dBm) to the

balanced audio input terminal block TB1-

1 (+), TB1-2 (-), and TB1-3 (ground). If

stereo/composite audio is provided,

connect it to BNC jack J6, the composite

audio input jack on the remote interface

panel. Jacks J3 and J13 on the rear of

the VHF exciter tray are loop-through

connected and the unused jack J13 can

be used as an audio source for another

transmitter by removing jumper W1 on

jack J15 on the aural IF synthesizer.

Look at the front panel meter on the VHF

exciter tray. In the Video position, the

meter indicates active video from 0 to 1

Vpk-pk. The normal video input level is 1

Vpk-pk on the meter. If this reading is

not at the proper level, the overall video

level can be changed by adjusting the

video level control R12 on the sync tip

clamp/ modulator board.

Switch the meter to the Audio position,

which shows the audio deviation,

modulation level, of the signal from 0 to

100 kHz. The aural IF synthesizer board

was factory set for a ±25 kHz deviation

with a balanced audio input of +10 dBm.

If the reading is at not the correct level,

adjust the balanced audio gain pot R13

on the aural IF synthesizer board, as

needed, to attain the ±25 kHz deviation.

The aural IF synthesizer board was

factory set for a ±75 kHz deviation with a

composite audio input of 1 Vpk-pk. If

this reading is not correct, adjust

composite audio gain pot R17 on the

aural IF synthesizer board, as needed,

for the ±75 kHz deviation.

2000-Watt VHF Low Band Transmitter Chapter 5, Detailed Alignment Procedures

334B, Rev. 0 5-2

5.2 (A4) VHF low-Band Exciter Tray

with the 4.5-MHz Composite Input

Kit (NOTE: If your transmitter does not

contain the 4.5MHz composite input kit,

skip this section.)

With the 4.5-MHz composite input kit,

the (A4) VHF exciter tray is able to

operate using either the separate video

and audio baseband inputs or the single

4.5-MHz composite input. The 4.5-MHz

composite input kit includes a composite

4.5-MHz filter board (1227-1244) and a

4.5-MHz bandpass filter board (1265-

1307).

To align the VHF exciter using baseband

video and audio, refer to the alignment

instructions described in Section 5.1 of

this chapter. Select the baseband input

operation by a applying a baseband

select, using a jumper or closed contacts,

connected between J7-6 and J7-7 on the

rear of the tray.

To operate the transmitter using the 4.5-

MHz composite input, remove the

baseband select command from J7-6 and

J7-7 on the rear of the tray.

Connect a multiburst test signal from an

envelope delay measurement set to the

input of the rear interface panel at J2.

On (A24) the composite 4.5-MHz filter

board (1227-1244), connect an

oscilloscope between J7, the center pin,

and pin 1 or 3, which are ground. Adjust

C21, if necessary, for the best frequency

response. Adjust R32 for a signal level of

1 Vpk-pk on the oscilloscope. The output,

as measured at J6 and J7 of the board,

should be video only with a minimum

4.5-MHz aural subcarrier.

On the (A25) 4.5-MHz bandpass filter

board (1265-1307), adjust the filter with

L2, C3, L4, and C7 for a frequency

response of no greater than ±.3 dB from

4.4 to 4.6 MHz. Adjust C19 for an overall

peak-to-peak variation of less than ±.3

dB from 4.4 MHz to 4.6 MHz. Recheck

the frequency response; it may have

changed with the adjustment of the

envelope delay.

5.3 (A4) VHF Exciter Tray with either

Baseband or the 4.5-MHz Composite

Input

The IF section of the (A4) VHF exciter

tray includes adjustments for automatic

level control (ALC), linearity (amplitude

predistortion), and phase (phase change

vs. level) predistortion for correction of

the nonlinearities of the RF amplifier

trays. The upconverter section also

includes adjustments to the local

oscillator chain tuning and the local

oscillator center frequency tuning. Both

of these were completed at the factory

and should not require adjustments at

this time.

Move the Operate/Standby switch on the

VHF exciter tray to Standby. The setup

of the RF output includes an adjustment

to the drive level of the three VHF

amplifier trays, the adjustment of the

linearity and phase predistortion (which

compensate for any nonlinear responses

of the amplifier trays), and the gain and

phasing adjustments of the three VHF

amplifier trays.

Verify that all of the red LEDs on the ALC

board are extinguished. The following

list describes the meaning of each LED

when they are illuminated:

• DS1 (Input Fault) – Indicates that an

abnormally low or no IF is present at

the input of the board

• DS2 (ALC Fault) – Indicates that the

ALC circuit is unable to maintain the

signal level requested by the ALC

reference. This is normally due to

excessive attenuation in the linearity

signal path or the IF phase corrector

signal path or because jumper W3 on

J6 is in the Manual ALC Gain position.

• DS3 (Video Loss) – Indicates a loss of

video at the input of the board

2000-Watt VHF Low Band Transmitter Chapter 5, Detailed Alignment Procedures

334B, Rev. 0 5-3

• DS4 (Mute) – Indicates that a visual

Mute command is present. (NOTE:

not used in this configuration)

• DS5 (Modulator Enable) – Indicates

that the modulator IF output has

been selected (NOTE: this is only

used if a receiver tray is present in

the system. DS5 is always on with

no receiver present.)

The ALC is muted when the transmitter is

in Standby. To monitor the ALC, turn off

the three VHF amplifier trays on/off

circuit breakers on the front panel of the

trays switch the transmitter to Operate.

Adjust the power adjust gain pot on the

front panel of the VHF exciter tray to

obtain +0.8 VDC on the front panel

meter in the ALC position. On the ALC

board (1265-1305), move the jumper W3

on J6 to the Manual position, between

pins 2 and 3, and adjust R87 on the ALC

board for +0.8 VDC on the front panel

meter in the ALC position. Move jumper

W3 back to Auto (between pins 1 and 2);

this is the normal operating position.

The detected IF signal level at J19-2 of

the ALC board is connected to the

transmitter control board that distributes

the level to the three VHF amplifier trays

where it is used as a reference for the

automatic gain control (AGC) in each

amplifier tray.

5.4 IF Phase Corrector Adjustment

As shipped, the exciter was preset to

include linearity (gain vs. level) and

phase (phase vs. level) predistortion. The

predistortion was adjusted to

approximately compensate the

corresponding non-linear distortions of

the VHF amplifier trays and should not

require additional adjustments.

Locate (A9) the IF phase corrector board

(1227-1250) mounted in the VHF exciter.

The amplitude correction portion of the

board is not utilized in this configuration.

As a result, jumper W3 on J10 should be

in the Disable position, to +6.8 VDC, and

R35 and R31 should be fully counter-

clockwise (CCW). R68 is the range

adjustment and should be set in the

middle of the range. The phase

correction Enable/Disable jumper W2 on

J9 should be in the Enable position, to

ground.

Switch the input video test source to

select an NTSC 3.58-MHz modulated

staircase or ramp test waveform. Set

up the station demodulator and

monitoring equipment to monitor the

differential phase or intermodulation

products of the RF output signal. There

are three corrector stages on the IF

phase corrector board, each with a

magnitude and a threshold adjustment

that are adjusted, as needed, to correct

for any differential phase or

intermodulation problems. Adjust the

R3 threshold for the cut-in point of the

correction and the R7 magnitude for the

amount of the correction that is needed.

Jumper W1 on J8 is set to give the

desired polarity of the correction shaped

by the threshold R11 and the magnitude

R15 adjustments. After setting the

polarity, adjust the R11 threshold for the

cut-in point of the correction and the R15

magnitude for the amount of the

correction that is needed. Finally, adjust

the R19 threshold for the cut-in point of

the correction and the R23 magnitude for

the amount of the correction that is

needed.

NOTE: Adjusting these pots changes all

visual parameters and should be done

cautiously and only if necessary.

5.5 Linearity Corrector Adjustment

The IF linearity correction function

consists of three non-linear cascaded

stages, each having adjustable

magnitude and threshold, or cut-in

points, located on the ALC board. The

threshold adjustment determines at what

IF signal level the corresponding

corrector stage begins to increase gain.

The magnitude adjustment determines

the amount of gain change for the part of

the signal that exceeds the corresponding

2000-Watt VHF Low Band Transmitter Chapter 5, Detailed Alignment Procedures

334B, Rev. 0 5-4

threshold point. Refer to the assembly

drawing for the ALC board (1265-5305),

to find the adjustments for the first

through third linearity corrector stages.

Because the stages are cascaded, the

order of correction is important. The first

stage should cut in near white level, with

the cut-in point of the next stage toward

black, and with the last stage primarily

stretching sync.

To adjust the linearity correctors from

scratch, ensure that the transmitter is

operating at full power with the desired

A/V ratio. Check that jumper W1 on J4

on the ALC board is in the linearity

enabled position, between pins 1 and 2.

Make sure that the ALC voltage is set to

+0.8 VDC as monitored on the front

panel meter in the ALC position.

Insert a modulated ramp video test

signal into the transmitter. Demodulate

the output signal of the transmitter and

observe the waveform on a waveform

monitor while also looking at the signal

on a spectrum analyzer. On the ALC

board (1265-1305), preset pots R34,

R37, and R40 (threshold, cut in) fully

CCW and the magnitude adjustments

R13, R18, and R23 fully clockwise (CW).

On the IF phase corrector board (1227-

1250), preset pots R7, R15, R23, and

R35 fully CW and R3, R11, R19, and R31

fully CCW.

Set the waveform monitor to differential

step filter and the volts/division scale to

.1 volts. Center the display to

approximately the blanking level.

Gradually adjust pots R3, R11, and R19

clockwise on the IF phase corrector

board, as needed, to minimize the

observed thickness of the

intermodulation as seen on the display.

Adjust pots R34, R37, and R40 clockwise

on the ALC board, as needed, to give

correction at sync or at low luminance

levels as viewed at the left-most edge of

the waveform monitor.

The intermodulation beat products

between the colorburst and the aural

carrier at 920 kHz above visual carrier

should also be observed on the spectrum

analyzer while performing the preceding

adjustments. The frequency will vary for

different video systems. When the

adjustments are performed properly, the

intermodulation products on the

spectrum analyzer should be at least -52

dB down, with a red field input, from

peak visual carrier. The intermodulation

distortion as displayed on the waveform

monitor should be no more than 1 IRE.

Pot R31 on the IF phase corrector board

is used for any extra intermodulation

correction that may be needed.

NOTE: Any adjustments to the above

pots affects other visual parameters and

some slight adjustments of all of the pots

may be needed to meet all specifications

simultaneously.

If the transmitter is being driven very

hard, it may not be possible to get

enough sync stretch while maintaining a

flat differential gain. In this case, some

video sync stretch may be used from the

sync tip clamp/modulator board; the

sync stretch adjustment is R48.

Switch the transmitter to Standby.

5.6 (A6, A7 and A11) Low-Band VHF

Amplifier Tray (1304363; Appendix

NOTE: The following procedure should

be fallowed only if complete alignment

of a VHF amplifier tray is needed.

The (A6, A7, and A11) low-band VHF

amplifier trays have been adjusted at the

factory to meet all specifications,

including phase adjustment to match the

multiple trays in an amplifier array when

they are combined. The trays should not

need to be adjusted to attain normal

operation. If necessary, any adjustments

to the boards in this tray should be

performed in the Manual Gain position,

with S1 on (A13) the AGC control board

2000-Watt VHF Low Band Transmitter Chapter 5, Detailed Alignment Procedures

334B, Rev. 0 5-5

(1142-1601) in Manual. The idling

currents for the amplifier boards are

adjusted with no RF drive applied.

Remember to put S1 back to the Auto

AGC position after any adjustments.

Auto AGC is the normal position during

operation of the transmitter.

Connect a dummy load with a rating of at

least 750 watts to J2, the RF output jack

of the tray being aligned, before

beginning the alignment procedure.

Switch the VHF amplifier tray on and the

transmitter to operate.

5.6.1 (A13) AGC Control Board

(1142-1601; Appendix D)

Using a calibrated wattmeter, check that

the tray is operating at the rated power.

Remove the sample forward power

connection J4 from the (A13) AGC control

board (1142-1601). The output power

level should drop to 20% because of the

VSWR cutback and DS4, the VSWR

Cutback LED, should be illuminated. The

front panel Module Status LED should not

be lit.

Reconnect J4 and adjust R59 so that it

begins to cut back on the output power

level when the reflected level increases

above 20%.

In the Power Supply Voltage position, the

front panel meter is calibrated to +30

VDC using R86 on the AGC control board.

5.6.2 (A2-A1) Phase Shifter Board

(1198-1602; Appendix D)

There are no adjustments to (A2-A1) the

phase shifter board (1198-1602). The

front panel has adjustments for phase

that are made during the amplifier array

setup procedure. Typically +7 dBm input

and +7 dBm output.

5.6.3 (A2-A2) VHF Filter/Amplifier

Board (1198-1606; Appendix D)

The (A2-A2) VHF filter/amplifier board

(1198-1606) has approximately 14 dB of

gain. Tune the channel filter capacitors

C29 and C20 (loading), C26 and C23

(center frequency), and C24 (coupling) at

J6 on the board for the best response.

Set voltage adjust pot R19 for +24 VDC

at the anode of CR5.

The idling current, no RF drive applied, of

the device Q1 is set for 250 mA. To set

the current, remove the RF drive,

measure the voltage across R16 (a 1Ω

resistor on the filter/amplifier board) and

adjust R13 for .25 volts (using Ohms’

Law: [E=I x R] : [E=250 mA x 1 Ω] :

E=250 mV). Typically the board has a

+7 dBm input and a +19.5 dBm output

level.

5.6.4 (A3-A1) VHF Low-Band

Amplifier Board (1198-1605;

Appendix D)

The (A3-A1) VHF low-band amplifier

board (1198-1605) has 22 dB of gain and

is biased for 3 amps of idling current, no

RF drive applied. Adjust voltage adjust

pot R10 for +24 VDC at pin 0 of the

regulator IC U1. To set the bias, remove

the RF drive from the board, measure the

voltage across R6 and R7 (two 1Ω

resistors in parallel on the high-band

driver board), and adjust R4 for 1.5 volts

(using Ohms’ Law: [E=I x R] [E=3 amps

x .5 Ω] : E=1.5 volts).

Connect a spectrum analyzer to output

jack J2 on the board and adjust C15 for

peak output. Typically +19.5 dBm input

and +41.5 dBm output.

5.6.5 (A3-A2) Overdrive Protection

Board (1198-1601; Appendix D)

The typical input level to the (A3-A2)

overdrive protection board (1198-1601)

is +41.5 dBm during normal operation

with a typical output of +41.3 dBm.

To set up the overdrive circuit, check that

the output power level of the transmitter

is at 100% and adjust R11 on the board

for a reading of .4 VDC at TP1. Increase

the output power level of the transmitter

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334B, Rev. 0 5-6

to 110%, sync only, and adjust R12 until

the output power begins to drop off.

Return the output power level of the

transmitter to 100%.

5.6.6 (A3-A3) 3-Way Splitter Board

(1198-1608; Appendix D)

There are no tuning adjustments for (A3-

A3) the 3-way splitter board. The board

takes the +41.3 dBm input and splits it

into three equal +36.3 dBm outputs.

5.6.7 (A4-A1, A4-A2, and A4-A3)

VHF Low-Band Amplifier Pallet

(1304348; Appendix D)

These pallets, P400-VHF-L, are supplied

by Delta RF Technology, Inc. Refer to

the data sheets in the subassembly

section of this manual for more

information. Each board has

approximately 18 dB of gain and with an

input of +36.3 dBm the output is

typically +54.3 dBm.

5.6.8 (A5-A1) 3-Way Combiner

Board (1198-1626; Appendix D)

There are no adjustments to the (A5-A1)

3-way combiner board. The three +54.3

dBm inputs are combined to produce the

750 watts, +58.8 dBm, peak of sync

output at J2 of the combiner assembly.

5.6.9 Calibration of the Visual Plus

Aural Output Power and VSWR

Cutback of the Tray

Check that a dummy load of at least 750

watts is connected to the output of the

tray that is to be calibrated. Place switch

S1 on the AGC control board in the

Manual position before beginning the

setup.

To adjust the visual output power levels:

1. Remove the J16 cable from (A5) the

sync tip clamp/modulator board

(1265-1302) in the VHF exciter tray.

Set the Manual AGC switch S1, on the

(A13) AGC control board (1142-1601)

in the VHF L.B. amplifier tray, to the

Manual position. Turn the transmitter

to the Operate position.

2. Connect a sync and black test signal

to the video input jack of the remote

interface panel.

3. Adjust the manual gain pot R5 on the

AGC control board for:

• Sync + black 0 IRE setup;

wattmeter=450 watts

• Sync + black 7.5 IRE setup;

wattmeter=405 watts

NOTE: The transmitter must have 40 IRE

units of sync.

4. Obtain a zero span reference of the

visual-only carrier on a spectrum

analyzer. Replace the J16 connector

on the sync tip clamp/modulator

board in the VHF exciter tray. Adjust

R5 on the AGC control board until the

same visual reference is obtained.

Adjust R44 on the AGC control board

for 100% Forward Power.

Lower the forward power reading to 80%

on the front panel meter using R5, the

manual gain adjust on the AGC control

board. Adjust R65, the AGC fault adjust

on the AGC control board, until the green

Module LED DS3 on the front panel just

begins to light. Use R5 to readjust the

forward power to 100%.

Switch off the tray and reverse the J6

and J7 cables on the 3-way combiner

enclosure.

Switch on the tray and adjust the front

panel meter, in the Reflected Output

Power position, to a 100% reading using

R53, the reflected power meter adjust on

the AGC control board. Adjust the

reflected output power to a 20% reading

using R5 on the AGC control board.

Adjust R59, the VSWR cutback adjust on

the AGC control board, until the red

VSWR Cutback LED DS4 on the front

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334B, Rev. 0 5-7

panel lights. This sets up the VSWR

cutback circuitry.

Readjust R5 for 100% on the meter to

achieve a 750 watts peak of sync output

+ 75 watts aural power. However, if the

system requires less output power per

amplifier tray, adjust each tray by the

same amount to give the desired total

output power.

Switch off the tray and return the J6 and

J7 cables on the 3-way combiner

assembly, back to their original positions.

If the tray was originally operating below

100% output power, the AGC fault adjust

was set for 20% below the operational %

Output Power of the tray. See the Test

Data Sheet for the transmitter for the

actual readings for the tray. Place S1 on

the AGC control board in the AGC

position. This is the normal operating

position after the setup is completed.

The VHF amplifier tray is aligned,

calibrated, and ready for normal

operation. Repeat as needed for the

other VHF amplifier trays.

5.7 Phase and Gain Adjustment of

multiple VHF Amplifier Trays

The following procedure was completed

at the factory and should only be

followed if one of the VHF amplifier trays

is replaced.

Adjust the gain controls located on the

VHF Amplifier Trays full CCW. Switch On

the front panel AC Circuit Breaker on the

bottom VHF amplifier tray. Place the

Transmitter in Operate and adjust the

Gain control on the Amplifier Tray for

50% output power and adjust the Phase

control to mid range. Monitor the output

power of the Transmitter by connecting a

Spectrum Analyzer to a sample of the

output. Adjust the Spectrum Analyzer

for Zero Span operation. The power

could be monitored by watching the

meters on the panel but the power

change is easier to see on the analyzer.

Turn On the AC to the middle amplifier

tray and adjust its' output power to 50%.

While monitoring the output power of the

Transmitter, adjust the Phase Control

until the power reaches a peak. If the

Phase adjust reaches its end of travel,

add a 4 inch cable to the RF Input (J1) of

the amplifier. Re-adjust the Phase to

peak the System output power. If the

Phase Control again reaches its end of

travel before a peak in power is reached,

add a 3 inch cable to J1 of the amplifier

and readjust phase for peak output

power. The adding of cables should be

done during the adjustment anytime the

range of the phase adjust needs

extended.

Turn On the AC to the top amplifier tray

and adjust its' output power to 50%.

While monitoring the output power of the

Transmitter, adjust the Phase Control

until the power reaches a peak. If the

Phase adjust reaches its end of travel,

add a 4 inch cable to the RF Input (J1) of

the amplifier. Readjust the Phase to

peak the System output power. If the

Phase Control again reaches its end of

travel before a peak in power is reached,

add a 3 inch cable to J1 of the amplifier

and readjust phase for peak output

power. The adding of cables should be

done during the adjustment anytime the

range of the phase adjust needs

extended.

Increase the output power on the bottom

and middle amplifier trays to 90%.

Adjust the Phase Control on the middle

amplifier tray to peak the System output

power.

Increase the output power on the top

amplifier to 90% and adjust the Phase

control for maximum System output

power.

Monitor the Reflected Power on all of the

VHF Amplifier Trays. The Reflected

Power should read <5%. If an amplifier

is showing high reflected power, adjust

the Phase control as needed to minimize

2000-Watt VHF Low Band Transmitter Chapter 5, Detailed Alignment Procedures

334B, Rev. 0 5-8

Reflected Power. Be careful not to

increase Reflected Power on the other

Amplifier Trays. The Amplifier Trays

should interact in such a way that the

phasing of any one amplifier tray will

affect the Reflected on the other amplifier

trays.

Raise or lower the output power of each

tray as needed to achieve 100% Output

Power. The output power of each tray

should be 90% to 100%.

5.8 Calibration of the Forward

Output Power Level of the

Transmitter

NOTE: Only perform the following

procedure if the forward power

calibration is suspect.

Switch the transmitter to Standby and

preset R51, the aural null pot on the

visual/aural metering board (1265-

1309), fully CCW. Adjust R48, the null

offset pot on the visual/aural metering

board, for 0% Visual Output. Perform

the following adjustments with no aural

present. This is accomplished by

removing jumper cable W1, the aural IF

loop-through, that is connected to J16 on

(A5) the sync tip clamp/modulator board

(1265-1302). Connect a sync and black

test signal to the video input jack of the

VHF exciter tray. Switch the transmitter

to Operate.

Next, set up the transmitter for the

appropriate average output power level:

• Sync + black 0 IRE

setup/wattmeter=1190 watts

• Sync + black 7.5 IRE

setup/wattmeter=1090 watts

NOTE: The transmitter must have 40 IRE

units of sync.

Adjust R28, visual calibration, on (A19)

the visual/aural metering board (1265-

1309) for 100% on the front panel meter

in the % Visual Output position.

With the spectrum analyzer set to the

zero span mode, obtain a peak reference

on the screen. Reconnect jumper cable

W1 to J16 on (A5) the sync tip

clamp/modulator board. While in the

Visual Output Power position, adjust L3

for a minimum visual power reading.

Turn the power adjust pot on the front

panel until the original peak reference

level is attained. Peak L1 and C8 for a

maximum aural power reading and then

also adjust R20 for a 100% Aural Power

reading. Switch the transmitter to the

Visual Output Power position and adjust

R51, the aural null pot, for 100% Visual

Power.

5.9 Calibration of the Reflected

Output Level of the Transmitter

NOTE: Only perform the following

procedure if the reflected power

calibration is suspect.

Check that the transmitter is at 100%

forward power. Switch the transmitter to

Standby and move the reflected cable to

the other Incidental port on the A16

Coupler. Switch the transmitter to

Operate and adjust R39 on the

visual/aural metering board (1265-1309)

for a 10% reading in the Reflected Power

position. At this 10% reference power

reading, the VSWR LED mounted on the

front panel of the exciter should be

illuminated. If this LED is not lit, adjust

R22 on the transmitter control board in

the VHF exciter tray until the VSWR LED

just turns on. Turn the power adjust pot

slightly CCW and the LED should go out.

Turn the pot CW until the LED just turns

on. The reflected output power is now

calibrated.

Switch the transmitter to Standby. Move

the cable on A16 Coupler back to the

Reflected port.

Switch the transmitter to Operate and

adjust the front panel power pot for a

100% Visual Power reading.

2000-Watt VHF Low Band Transmitter Chapter 5, Detailed Alignment Procedures

334B, Rev. 0 5-9

5.10 (A8) 3-Way Combiner Assembly

(1065241; Appendix C)

There are no adjustments to (A8) the 3

way combiner assembly.

5.11 (A14) Bandpass Filter Assembly

(1304388; Appendix C)

The harmonic and bandpass filters are

factory swept by the filter manufacturer

and should not be tuned without the

proper equipment. Do not attempt to

tune the filters without a sweep

generator or, preferably, a network

analyzer. If tuning is required, consult

the Axcera Field Support Department

before attempting to make any

adjustments.

5.12 Complete Board Level

Alignment Procedures for the VHF

Low Band Exciter

NOTE: The following procedure should

be fallowed only if complete alignment

of the VHF exciter tray is needed.

5.12.1 (Optional) 4.5-MHz

Composite Input Kit

If the (optional) 4.5-MHz composite input

kit is purchased, the tray is capable of

operating by using either the 4.5-MHz

composite input or the baseband audio

and video inputs. The kit adds the (A24)

composite 4.5-MHz filter board (1227-

1244; Appendix D) and the (A25) 4.5-

MHz bandpass filter board (1265-1307;

Appendix D) to the transmitter. When the

4.5-MHz intercarrier signal generated by

the 4.5-MHz composite input has been

selected by the 4.5-MHz composite input

kit, the 4.5-MHz generated by the aural

IF synthesizer board is not used. When

the 4.5-MHz intercarrier signal generated

by the baseband video and audio inputs

with baseband has been selected by the

4.5-MHz composite input kit, the

composite 4.5-MHz filter board and the

4.5-MHz bandpass filter board are not

used.

The tray has been factory tuned and

should not need any alignments to

achieve normal operation. To align the

tray for the 4.5-MHz composite input,

apply the 4.5-MHz composite input, with

the test signals used as needed, to the

video input jack (J1 or J2 [loop-through

connections]) on the rear of the tray.

Select the 4.5-MHz composite input by

removing the baseband select from J18-6

and J18-7 on the rear of the tray.

To align the exciter using baseband video

and audio inputs, apply the baseband

video, with the test signals used as

needed, to the video input jack (J1 or J2

[loop-through connections]) and the

baseband audio to the proper baseband

audio input on the rear of the tray. For

balanced audio input, connect TB1-1(+),

TB1-2(-), and TB1-3 (GND). For

composite/stereo audio, connect the

composite audio input jack (J3 or J13

[loop-through connections]) and connect

a baseband select from J18-6 and J18-7

on the rear of the tray.

5.12.2 (A6) Delay Equalizer Board

(1227-1204; Appendix D)

The jumper W1 on J5 of the sync tip

clamp/modulator board, if present, must

be in the Enable position between pins 2

and 3.

NOTE: This board has been factory tuned

and should not be retuned without the

proper equipment.

To tune this board:

1. Connect a sinX/X test signal into

jack J1-2 on the delay equalizer

board.

2. Monitor the video output of the

board, at the video sample jack J2,

with a video measuring set, such as

the VM700, adjusted to measure

group delay.

3. Tune the four stages of the board

using the variable inductors (L1-L4)

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334B, Rev. 0 5-10

and potentiometers (R7, R12, R17,

and R22) until the signal attains the

FCC group delay curve. The stages

are arranged in order of increasing

frequency. Adjust R29, as needed,

to attain the same level out of the

board as into the board.

5.12.3 (Optional) (A24) Composite

4.5-MHz Filter Board (1227-1244;

Appendix D)

This board is part of the 4.5-MHz input

kit and will only function properly with a

4.5-MHz composite input signal and the

4.5-MHz composite input selected. To

align this board:

1. Connect the test signal from an

envelope delay measurement set to

the video input of the tray at J1 or

J2.

2. Connect an oscilloscope to jack J7,

video out, between the J7 center

pin and pin 1 or 3 (ground). Adjust

C21, frequency response, if needed,

for the best frequency response.

Adjust R32, video gain, for a signal

level of 1 Vpk-pk on the

oscilloscope.

The output at J6 and J7 on the board

should be video only, without the 4.5-

MHz aural subcarrier.

5.12.4(Optional) (A25) 4.5-MHz

Bandpass Filter Board (1265-1307;

Appendix D)

This board is part of the 4.5-MHz input

kit and will only function properly with a

4.5-MHz composite input signal and the

4.5-MHz composite input selected. To

align this board:

1. Adjust the filter with L2, C3, L4,

and C7 for a frequency response of

no greater than ±0.3 dB from 4.4

to 4.6 MHz.

2. Adjust C19 for an overall peak-to-

peak variation of less than ±0.3 dB

from 4.4 MHz to 4.6 MHz.

3. Recheck the frequency response; it

may have changed with the

adjustment of the envelope delay.

If necessary, retune the board.

5.12.5 (A7) IF Carrier Oven

Oscillator Board (1191-1404;

Appendix D)

NOTE: If your transmitter contains a

precise frequency control system, an IF

VCXO Board (1248-1131) will replace the

IF Carrier VCXO Board. . Refer to the

precise frequency control instruction

manual for set up details.

To align this board:

1. While monitoring J3 with a

spectrum analyzer, observe the

45.75-MHz visual IF (typical +5

dBm).

2. Connect a frequency counter to J3

and adjust C17 for 45.750000 MHz.

3. Connect a frequency counter to J1

and check for 50 kHz, which is the

aural phase lock loop reference.

5.12.6 (A5) Sync Tip

Clamp/Modulator Board (1265-

1302; Appendix D)

To align this board:

1. Determine if jumper W4 on jack J3

is present. Jumper W4 terminates

the video input into 75Ω. Remove

jumper W4 if a video loop-through

is required on the rear chassis at

jacks J1 and J2.

2. Set the controls R20, the white clip,

R24, the sync clip, and R45, the

sync stretch cut-in, to their full

CCW position. Set R48, the sync

magnitude, fully CW and place the

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334B, Rev. 0 5-11

jumper W7 on jack J4 to the

Clamp-Off, Disable, position.

3. Connect a 5-step staircase video

test signal to the input of the

transmitter.

4. Monitor TP2 with an oscilloscope.

Adjust R12, the video gain pot, for

1 Vpk-pk.

5. Change the video input test signal

to a multiburst test pattern. While

monitoring TP2, adjust C8 and R32

for a flat-frequency response.

Change the input video test signal

back to the 5-step staircase.

6. Monitor TP2 with an oscilloscope.

Adjust pot R41, manual offset, for a

blanking level of -0.8 VDC. The

waveform shown in Figure 5-1

should be observed. Move the

jumper W2 on J4 to the Clamp

Enable position. Adjust pot R152,

depth of modulation, for a blanking

level of -0.8 VDC.

NOTE: This waveform represents the

theoretical level for proper

modulation depth. Step 9 below

describes how to set the modulation

depth through the use of a television

demodulator or a zero-spanned

spectrum analyzer tuned to the

visual IF frequency.

Figure 5-1. Waveform

7. The following test setup is for the

adjustment of the depth of

modulation and ICPM at IF:

A. Remove the cable that is on

J18 and connect the double-

sideband, 45.75-MHz visual IF

signal from J18 to a 10-dB

splitter/coupler. Connect the

coupled port of the

splitter/coupler to the RF input

of a television demodulator.

Connect the direct port to a

spectrum analyzer.

B. Connect the 75Ω video output

of the demodulator to the video

input of a waveform monitor.

For ICPM measurements, also

connect the quadrature output

of the demodulator to the

horizontal input of the

waveform monitor using a 250

-kHz, low-pass filter. (An

oscilloscope can be used in

place of a waveform

monitor).

C. Set the controls of the

demodulator to the following:

Detector mode – Cont

Sound trap – In

Zero carrier – On

Auto – Sync

Audio source – Split

De-emphasis – In

8. Move jumper W7 on J4 to the

Clamp Disable position. Readjust

pot R41, manual offset, for the

correct depth of modulation by

observing the demodulated

waveform on the waveform monitor

or on the spectrum analyzer set to

zero span.

9. Check the demodulated video for a

proper sync-to-video ratio (sync is

28.6% of the total white video

signal). If sync stretch is needed,

adjust R45, sync stretch cut-in,

until sync stretch occurs. Adjust

R48, sync stretch magnitude, for

the proper amount of stretch.

Readjust R41, manual offset, if

needed, for the correct depth of

modulation.

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334B, Rev. 0 5-12

10. Move jumper W7 on J4 to the

Clamp Enable position. Readjust pot

R152, depth of modulation, for the

correct depth of modulation.

11. Set the waveform monitor to

display ICPM. Preset R53 fully CCW,

adjust C78 for the greatest effect at

white on the ICPM display, and then

adjust R53 for minimum ICPM.

12. Recheck the depth of modulation

and, if necessary, adjust R152,

depth of modulation.

13. On a spectrum analyzer, adjust pot

R70 for a level of approximately -10

dBm at J18.

14. Remove the input video test signal.

Place the front panel meter in the

video position and, while monitoring

the meter, adjust pot R144, zero

adjust, for a reading of zero.

15. Replace the input video test

signal (the 5-step staircase).

Turn the front panel meter to

the video position and adjust

R20 on the transmitter control

board for a reading of 1 volt

(10 on the 0 to 10 scale). This

board does not have sync

metering.

16. Reconnect the plug to J18 and

move the spectrum analyzer test

cable to the 41.25 IF output jack

J16. Tune C59 and L17 to L20 to

maximize the 41.25-MHz aural IF

signal and minimize the out-of-

band products. Adjust pot R97 for

-20 dBm at J16.

17. Reconnect the plug to J16 and

move the spectrum analyzer test

cable to IF output jack J20. Preset

R62, the visual IF gain pot, to the

middle of the range. Insert a

multiburst test signal into the

transmitter and observe the visual

frequency response with the

spectrum analyzer set at 1

dB/division. Tune R63 and C30,

the IF frequency response

adjustments, for a flat-frequency

response (±0.5 dB).

18. While still monitoring J20 with a

spectrum analyzer, readjust R62,

visual IF gain, for a 0 dBm visual

output level. Adjust R85, A/V ratio,

for a minus 10 dB aural-to-visual

ratio or to the desired A/V ratio.

Reconnect the plug to J20.

19. Using an input video test signal (the

5-step staircase) with 100 IRE

white level, monitor TP2 with an

oscilloscope. Set control R24, the

sync clip, just below the point

where sync clipping begins to occur.

Similarly, set R20, the white clip, to

just below the point at which the

white video begins to clip.

5.12.7 (A4) Aural IF Synthesizer

Board, 4.5 MHz (1265-1303;

Appendix D)

1. To set up the test equipment for

this board:

A. Connect the 600Ω balanced

audio output from an audio

oscillator to the balanced audio

input terminals of the tray at

TB1-1 (+), TB1-2 (-), and TB1-

3 (ground) on the rear chassis.

B. Connect the combined IF

output at J21 (IF sample) on

the clamp modulator board to

the input of an IF splitter.

Connect one output of the

splitter to the video

demodulator and the other

output to the spectrum

analyzer.

C. At the front of the

demodulator, connect a short

cable from the RF-out jack to

the IF-in jack.

2000-Watt VHF Low Band Transmitter Chapter 5, Detailed Alignment Procedures

334B, Rev. 0 5-13

D. Connect a cable from the 600Ω

audio output jack of the

demodulator to the input of an

audio distortion analyzer.

2. Set the output frequency of the

audio oscillator to 400 Hz and the

output level to +10 dBm.

3. Center the aural carrier on the

spectrum analyzer with the

spectrum analyzer set to the

following:

Frequency/Division – 10 kHz

Resolution bandwidth – 3 kHz

Time/Division – 50 msec

Trigger – Free run

A. Adjust L5 for approximately

+3.5 VDC at TP2.

B. The green LED DS1 should be

illuminated, indicating a locked

condition. If not, retune L5 for

a locked condition.

4. Adjust R13, balanced audio gain, on

the aural IF synthesizer board for

±25-kHz deviation.

5. Check the distortion on the aural

distortion analyzer (THD=< 0.5%).

6. Disconnect the 600Ω balanced

audio input to the tray. Connect a

75Ω stereo audio input (400 Hz at 1

Vpk-pk) to composite audio input

jack J3 on the rear of the tray.

Follow the procedure in the stereo

generator instruction manual for

matching the level of the generator

to the exciter. Use R17 to adjust

the composite audio gain.

7. Check the distortion level on the

distortion analyzer (THD)=< 0.5%)

5.12.8 (A8) ALC Board (1265-1305;

Appendix D) (Part 1 of 2)

Table 5-1 describes the functions of each

LED on the ALC board (A8).

Table 5-1. ALC Board LEDs

LED FUNCTION

DS1 (Red LED) Indicates that an abnormally low IF signal level is present at

IF input connector J1

DS2 (Red LED)

Indicates that the ALC circuit is unable to maintain the level

requested by the ALC reference due to excessive attenuation

in the linearity or the IF phase corrector signal path or

because jumper W3 on J6 is in manual gain

DS3 (Red LED) Indicates a video loss fault

DS4 (Red LED) Indicates that a Mute command is present

DS5 (Green LED) Indicates that the output from the modulator is selected as

the input to the board

1. To align the ALC board, preset the

following controls on the tray:

A. ALC Board (1265-1305)

Connect jumper W1 on J4 to

disable, between pins 2 and 3 (to

disable linearity correctors).

Connect jumper W3 on J6 to

manual, between pins 2 and 3 (for

manual gain control).

Adjust R87, manual gain pot, to

mid-range.

B. IF Phase Corrector Board (1227-

1250)

Move W2 on J9 to phase

correction: enable. Move W3 on

J10 to amplitude correction:

disable.

2000-Watt VHF Low Band Transmitter Chapter 5, Detailed Alignment Procedures

334B, Rev. 0 5-14

2. The combined IF output of the sync

tip clamp modulator board is cabled

to jack J32 of the ALC board.

Remove J32 from the board, and

look to see if DS1, Input Fault, is

illuminated. Reconnect J32 and

make sure that DS1 is

extinguished.

3. Jumper W3 on J6 should be in the

Manual position. Monitor jack J3

with a spectrum analyzer.

4. With a multiburst video signal

present, tune C4 for a flat-

frequency response of ±0.5 dB.

5. Before proceeding with the second

part of the ALC board alignment,

check to see that the IF phase

corrector board (1227-1250) is

functioning properly.

5.12.9 (A9) IF Phase Corrector Board

(1227-1250; Appendix D)

This board is set up during system

alignment. The signal level into the

board should be approximately the same

as the output of the board.

The IF input jack (0 dBm) of the IF phase

corrector board is fed from the J3 IF O/P

jack of (A8) the ALC board.

The IF output jack of the IF phase

corrector board at J4 is fed to J7 IF I/P

jack (0 dBm) of the ALC board (A8).

5.12.10 (A8) ALC Board (1265-1305;

Appendix D) (Part 2 of 2)

To align this board:

1. Input a multiburst video test signal.

Connect a spectrum analyzer to

J11. Tune C63 for a flat-frequency

response of ±0.5 dB.

2. Move the Operate/Standby switch

on the front panel to the Operate

position.

3. Place jumper W3 on jack J6 in the

Manual mode and adjust R87 for

0.5 volts at TP4.

4. Place jumper W3 on J6 in the Auto

mode and adjust the front panel

power adjust control A20 fully CW.

If the (optional) remote power

raise/lower kit is present, then

adjust switch S1 on the board to

maximum voltage at TP4. Adjust

R74, the range adjust, for 1 volt at

TP4.

5. Adjust the front panel power adjust

control A20 for 0.5 VDC at TP4. If

the (optional) remote power

raise/lower kit is present, move

switch S1 on the board to mid-

range and then adjust (A20) the

front panel power adjust control for

0.8 VDC at TP4.

6. Disconnect the plug that is on J12

(IF output) and monitor J12 with a

spectrum analyzer. Verify an output

of approximately 0 dBm. If

necessary, adjust R99 to increase

the output level. If less of an output

level is needed, move jumpers J27

and J28 to pins 2 and 3 and then

adjust R99. Reconnect J12.

7. Move W2 on J5 to the Cutback

Enable position. Remove the input

video signal and verify that the

output of the transmitter drops to

25%. Adjust R71, the cutback level,

if necessary. Restore the input

video.

NOTE: The following step affects the

response of the entire transmitter.

8. Connect a video sweep signal to the

input of the tray. Monitor the

output of the system with a

spectrum analyzer. Adjust C71 with

R103 and C72 with R106, as

needed, to flatten the response.

C71 and C72 adjust for the

frequency of the correction notch

being applied to the visual response

2000-Watt VHF Low Band Transmitter Chapter 5, Detailed Alignment Procedures

334B, Rev. 0 5-15

of the transmitter. R103 and R106

are used to adjust the depth and

width of the correction notch.

9. The linearity correctors are set up

during the system alignment

procedure. Controls R13, R18, and

R23, the magnitude controls,

should be set fully CW. Controls

R34, R37, and R40 are the linearity

cut-in adjustments.

5.12.11 (A14-A1) Channel Oscillator

Board, Dual Oven (1145-1201;

Appendix D)

NOTE: If your transmitter contains a

precise frequency control system, a

VCXO Channel Oscillator Board (1145-

1204) will replace the Channel Oscillator

Board. Refer to the precise frequency

control instruction manual for set up

details.

This board is mounted in (A14) the

channel oscillator assembly (1145-1202).

To align the board:

1. Connect the main output of the

channel oscillator (J1) to a

spectrum analyzer, tuned to the

crystal frequency, and peak tuning

capacitors C6 and C18 for

maximum output. Tune L2 and L4

for maximum output. The output

level should be about +5 dBm. The

channel oscillator should maintain

an oven temperature of 50° C.

If a spectrum analyzer is not

available, connect a digital

voltmeter (DVM) to TP1 on the x4

multiplier board. Tune capacitors

C6 and C18 for maximum voltage,

then also tune L2 and L4 for a

maximum voltage output at TP1.

2. Connect the sample output of the

channel oscillator (J2) to a suitable

counter and tune C11, coarse

adjust, and C9, fine adjust, to the

crystal frequency.

3. Reconnect the main output (J1) of

the channel oscillator (+5 dBm) to

the input (J1) of the x2 multiplier.

NOTE: Do not repeak C6, C18, L2, or

L4. This may change the output level.

NOTE: While adjusting C9 and C11 to

the crystal frequency, the peak voltage

monitored at TP1 of the x4 multiplier

board should not decrease. If a decrease

does occur, there may be a problem

with the crystal. Contact Axcera Field

Support for further instructions.

NOTE: If the VCXO board (1145-1204) in

the VCXO assembly (1145-1206) is used,

the fine-frequency adjust C9 is not

located on the VCXO board. It is located

in the precise frequency tray. Refer to

the precise frequency control instruction

manual for set up details.

5.12.12 (A11-A1) x2 Multiplier Board

(1172-1111; Appendix D)

While monitoring the board with a DC

voltmeter, maximize each test point

voltage by tuning the broadband

multipliers in the following sequence:

1. Monitor TP1 with a DVM and tune

C4 for maximum voltage. Monitor

TP2 with a DVM and tune C6 for

maximum voltage. Repeak C4 and

C6 for maximum voltage.

2. Connect a spectrum analyzer,

tuned to two times the crystal

frequency, to the x2 multiplier

output jack J2. While trying to

keep the out-of-band products to

a minimum, monitor the output

and peak the tuning capacitors for

maximum output.

The output of the x2 multiplier (+15dBm)

connects to (A11-A1) the filter/mixer

board.

2000-Watt VHF Low Band Transmitter Chapter 5, Detailed Alignment Procedures

334B, Rev. 0 5-16

5.12.13 (A11-A2) VHF Filter/Mixer

Board (1153-1101; Appendix D)

Typically a +15dBm RF input at J3, a

0dBm combined IF input at J7, and a RF

output of 0dBm at J2.

To align the board:

1. Monitor J4, the LO output of the

board, with a spectrum analyzer

and adjust C12 and C18 for

maximum output (+14 dBm) at

the LO frequency and minimum

out-of-band products. Adjust C13

and C17 for the best frequency

response for the LO frequency.

2. Adjust C3 and C6 to determine

the center frequency. Use C2 and

C7 to locate the upper and lower

channel-edge shaping. C4 is used

to determine the channel

bandwidth.

5.12.14 (A11-A3) VHF Low-Band

Filter/Amplifier Board (1064251;

Appendix D)

The filter/amplifier board has been

factory swept and adjusted for a 6-MHz

bandwidth.

NOTE: This board should not be tuned

without the proper equipment.

The output of the filter/mixer board

connects to the board at J7 (0dBm). It is

filtered on the board with the filtered

output connecting to J1 on the board that

is amplified by U1 to a nominal +12 dBm

visual and +2 dBm aural level set by

adjusting R9. The output at J2 is fed to

J4 on the A11 enclosure and from there

to J15 the RF output jack on the rear of

the tray.

To align the board, use a multiburst or

sweep video signal inserted into the

exciter tray.

Check that there is a cable connected

from J6 to J1 on the filter/amplifier

board. Monitor J2, the RF output of the

board, and peak C17 for the maximum

signal level. Tune the manual gain

adjust R9 for a +12 dBm peak visual

output.

This completes the detailed alignment

procedure for the VHF Exciter Tray, the

VHF L.B. Amplifier Tray, and also the

detailed alignment procedures for the

entire 334B transmitter. If a problem

occurred during the alignment procedure,

please call Axcera field support at 724-

873-8100 for assistance.

APPENDIX A

SYSTEM SPECIFICATIONS

VHF Solid State Transmitter/Translator 300/400 Series

334B/336B 434B/436B

These low power VHF transmitters and translators deliver high quality and performance

in a compact and economical package. The time-proven Axcera exciter provides a

pre-corrected output directly to the high-gain  nal power ampli er modules. The

entire package is housed in a single 19 inch rack-mount cabinet.

Designed for high reliability and unattended operation, each power ampli er

utilizes a parallel ampli er design with a high level of protection circuitry. Features

such as VSWR cutback, overdrive protection and over-temperature protection ensure

on-air reliability. Convenient system monitoring is achieved through front panel

samples, status indicators and metering, most of which are remote controllable.

Speci cations published here are current as of the date of publication of this document. Because we are continuously improving our products, Axcera reserves the right to change speci cations

without prior notice. At any time, you may verify product speci cations by contacting our of ce. Axcera views it’s patent portfolio as an important corporate asset and vigorously enforces its patents.

Products or features contained herein may be covered by one or more U.S. or foreign patents.

0406R0

An Equal Opportunity Employer

A Platinum Equity Company

103 Freedom Drive, PO Box 525, Lawrence, PA 15055

t: 724-873-8100

f:724-873-8105

www.axcera.com

Visual Performance

Power Output

2000W

Output Impedance

Frequency Range

334B/336B

54 to 88 MHz

434B/436B

174 to 216 MHz

Carrier Stability

±250 Hz

(Transmitters or Translators with FCR)

Frequency Translation Stability

±1 kHz

(Translators)

Regulation of RF Output Power

Output Variation (Over 1 Frame)

Sideband Response

-1.25 MHz and below

-20 dB

-0.75 to -0.5 MHz

-+0.5, -2.0 db

-0.5 to +3.58 MHz

±0.5 dB

3.58 MHz to 4.18 MHz

=0.5, -1.0 dB

Freq Response vs. Brightness

±0.5 dB

Differential Gain

Incidental Phase Modulation

±3°

Linearity

(Low Frequency)

Differential Phase

±3°

Signal-to-Noise Ratio

55 dB

2t K-Factor

Envelope Delay

Transmitters

Per FCC

Standard

Translators

±40 ns

Video Input

(Transmitters)

Harmonic Radiation

-60 dB

Intermodulation Products

-52 (red  eld)

Spurious

-60 dBm

(>3 MHz from channel edge)

Noise Figure

(Translator)

4.5 dB (max)

With Input Preamp

Input Dynamic Range

-65 to -25 dBm

(Translators)

Aural Performance

Power Output

(Average)

200W

Distortion

0.5%

FM Noise

-60 dB

AM Noise

-55 dB

Aural to Visual Separation

4.5 MHz,

±100 Hz

Composite Audio Input

(Transmitters)

Input Level

1V peak,

nominal

Input Impedance

75 ohms,

unbalanced

Frequency Range

(±0.5 dB resp.)

30 Hz to

120 kHz

Monaural Audio Input

Input Level

0 to +10 dBm

Input Impedance

600 ohms,

balanced

Freq Range

(±0.5 dB resp.)

30 Hz to

15 kHz

Pre-emphasis

75µs

Subcarrier Input

(Transmitters)

Input Level

1V peak,

nominal

Input Impedance

75 ohms,

unbalanced

Freq Range

(±0.5 dB resp.)

20 kHz to

120 kHz

General

Operational Temperature Range

-30°C to +50°C,

derate 2°C per

1000 ft. AMSL

Operational Humidity Range

0% to 95%

(Non-condensing)

Altitude*

8,500 feet

Transmitter Dimensions

Size (H x W x D)

69”x22”x34”

Weight

500 lbs

Line Voltage

208 or 240 V ±10%,

1 phase 50/60Hz

Power Consumption

4000 W (50% APL)

Options

Automatic Station Identi er

Spare Parts Kit

Modulator Option

(Translators)

Remote Preampli er

(Translators)

UHF Frequency Correcting Receiver

(FCR Option,Translators)

VHF Solid State Transmitter/Translator 300/400 Series

334B/336B 434B/436B

APPENDIX B

SAMPLE LOG REPORT SHEET

AND TYPICAL READINGS

2000-Watt VHF Low Band Transmitter Appendix B, Sample Log Report Sheet

334B, Rev. 0 B-1

VHF Exciter (A4)

ALC (0 to 1 V) = ____________V % Aural Power (0 to 120) = __________%

% Exciter (0 to 120) = ______________% Video (0 to 1 V) = ________________IRE

% Reflected (0 to 120) = ____________% Audio (0 to 100 kHz) = ____________kHz

% Visual Power (0 to 120) = _________%

VHF Amplifier Trays

#1 (A6) #2 (A7)

AGC Voltage (0 to 10 V) = ___________V AGC Voltage (0 to 10 V) = ___________V

% Reflected Power (0 to 120) = _______% % Reflected Power (0 to 120) = _______%

% Output Power (0 to 120) = ________% % Output Power (0 to 120) = ________%

Power Supply Voltage (0 to 100 V) = ___V Power Supply Voltage (0 to 100 V) = ___V

Current (0 to 10A scale, readings are then

multiplied by 2) Current (0 to 10A scale, readings are then

multiplied by 2)

Current I1 = ___________A Current I1 = ___________A

Current I2 = ___________A Current I2 = ___________A

Current I3 = ___________A Current I3 = ___________A

Current ID = ___________A Current ID = ___________A

2000-Watt VHF Low Band Transmitter Appendix B, Typical Readings

334B, Rev. 0 B-3

VHF Low Band Exciter Tray (A4)

ALC = .8V

% Exciter = The level needed to attain 100% output power from the transmitter

(Typically between 80 & 100%).

% Reflected = < 10%

% Visual Power = 100 % (2000 Watts Peak of Sync)

% Aural Power = 100 % (200 Watts @ 10 dB A/V Ratio)

Video = 1 V at White w/.3V Sync Only, -40 IRE

Audio = ±25 kHz with Balanced Audio Input or ±75 kHz with Stereo Composite

Audio Input

VHF Amplifier Trays (A6, A7 & A11)

AGC Voltage = 1 to 3V

% Reflected Power = < 5%

% Output Power = 100%

Power Supply Voltage = 30V

Operating Currents Idling Currents

Current I1 = 12A-13A (Black Picture) 1.8A (No RF Applied)

Current I2 = 12A-13A (Black Picture) 1.8A (No RF Applied)

Current I3 = 12A-13A (Black Picture) 1.8A (No RF Applied)

Current ID = 3A (Black Picture) 3A (No RF Applied)

(The readings are from the 0 to 10A scale with the value then multiplied by 2)

2000-Watt VHF Low Band Transmitter Appendix B, Sample Log Report Sheet

334B, Rev. 0 B-2

VHF Amplifier Trays

#3 (A11)

AGC Voltage (0 to 10 V) = ___________V

% Reflected Power (0 to 120) = _______%

% Output Power (0 to 120) = ________%

Power Supply Voltage (0 to 100 V) = ___V

Current (0 to 10A scale, readings are then

multiplied by 2)

Current I1 = ___________A

Current I2 = ___________A

Current I3 = ___________A

Current ID = ___________A

Date __________________

Customer Name ______________________________ Call Letters ________________

Technician ___________________________________________

APPENDIX C

ASSEMBLY DRAWINGS AND PARTS LISTS

2000-Watt VHF Low Band Transmitter Appendix C, Assembly Drawings

334B, Rev. 0 C-1

334B System:

334B VHF Low Band Transmitter Typical Racking Plan............................1304405

334B VHF Low Band Transmitter Block Diagram....................................1304535

334B VHF Low Band Transmitter Interconnect .....................................1304391

334B VHF Low Band Transmitter Interconnect w/Gentner.......................1304518

VHF Low Band Exciter Tray, M/N, Sync Tip Clamp

Block Diagram................................................................................1070906

Interconnect.................................................................................1070908

VHF Low Band Amplifier Tray, CH. 5-6

Block Diagram................................................................................1304364

Interconnect.................................................................................1304365

APPENDIX D

SUBASSEMBLY DRAWINGS AND PARTS LISTS

2000-Watt VHF Low Band Transmitter Appendix D, Subassembly Drawings

334B, Rev. 0 D-1

Differential Gain Corrector Board

Schematic ..................................................................................1138-3107

AGC Control Board

Schematic ..................................................................................1142-3601

Channel Oscillator Board, Dual Oven

Schematic ..................................................................................1145-3201

VCXO Channel Oscillator Board, Dual Oven (Used with Precise Frequency)

Schematic ..................................................................................1145-3204

(Optional) IF Attenuator Board (Used with AM Identifier Kit)

Schematic ..................................................................................1150-3201

VHF Low Band Filter/Mixer Board

Schematic ..................................................................................1153-3101

x2 Multiplier Board, VHF Low Band

Schematic ..................................................................................1172-3111

IF Carrier Oven Oscillator Board, 45.75MHz

Schematic ..................................................................................1191-3404

Overdrive Protection Board

Schematic ..................................................................................1198-3601

Phase Shifter Board, VHF Low Band

Schematic ..................................................................................1198-3602

Low Band VHF Amplifier Board

Schematic ..................................................................................1198-3605

Filter/Amplifier Board

Schematic ..................................................................................1198-3606

3 Way Splitter Board (CH. 5-6)

Schematic ..................................................................................1198-3608

3-Way Combiner Board (CH. 5-6)

Schematic ..................................................................................1198-3626

Delay Equalizer Board

Schematic ..................................................................................1227-3204

IF Phase Corrector Board

Schematic ..................................................................................1227-3250

IF Carrier VCXO Board, NTSC (Used with Precise Frequency)

Schematic ..................................................................................1248-3131

Sync Tip Clamp/Modulator Board

Schematic ..................................................................................1265-3302

Aural IF Synthesizer Board, 4.5 MHz

Schematic ..................................................................................1265-3303

2000-Watt VHF Low Band Transmitter Appendix D, Subassembly Drawings

334B, Rev. 0 D-2

ALC Board

Schematic ..................................................................................1265-3305

(Optional) EEPROM FSK Identifier Board (Used with AM Identifier Kit)

Schematic ..................................................................................1265-3308

Visual/Aural Metering Board

Schematic ..................................................................................1265-3309

Transmitter Control Board

Schematic ..................................................................................1265-3311

+12V(4A)-12V(1A) Power Supply Board

Schematic ..................................................................................1265-3312

VHF Low Band Filter/Amplifier Board

Schematic .....................................................................................1064146

Current Metering Board, VHF Low Band

Schematic .....................................................................................1304366

P400-VHF-L-18 400W Pk. Sync VHF LB Pallet (1304348)

Delta RF Technology Data Sheet...................................................P400-VHF-L

UBS Axcera 334B 2000-Watt VHF Low Band Transmitter User Manual 334B

UBS-Axcera 2000-Watt VHF Low Band Transmitter 334B

Compiled Manual 334B

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