UBS Axcera 430B 1000-Watt VHF High-band Television Transmitter User Manual 430B

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INSTRUCTION MANUAL
430B
1-kW VHF High 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
1000 Watt VHF High Band Transmitter
Table of Contents
TABLE OF CONTENTS
CHAPTER 1 INTRODUCTION
1.1
1.2
1.3
1.4
1.5
1.6
Manual Overview............................................................................ 1-1
Assembly Designation Procedure ....................................................... 1-1
Safety.......................................................................................... 1-1
Maintenance.................................................................................. 1-2
Material Return Procedure ................................................................ 1-2
Limited One-Year Warranty for Axcera Products ................................... 1-3
CHAPTER 2 SYSTEM DESCRIPTION AND REMOTE INTERFACE CONNECTIONS
2.1 System Overview ........................................................................... 2-1
2.2 Control and Status.......................................................................... 2-2
2.2.1 VHF Exciter Tray .................................................................... 2-3
2.2.2 VHF High Band Amplifier Tray ................................................... 2-5
2.3 Input Connections .......................................................................... 2-6
2.4 AC Input to the transmitter .............................................................. 2-6
2.5 Remote Interface Connections .......................................................... 2-6
CHAPTER 3 INSTALLATION AND SETUP PROCEDURES
3.1
3.2
3.3
3.4
Site Considerations......................................................................... 3-1
Unpacking the Cabinets and Trays ..................................................... 3-4
Installing the Cabinets and Trays....................................................... 3-5
Setup and Operation....................................................................... 3-6
CHAPTER 4 CIRCUIT DESCRIPTIONS
4.1 VHF High Band Exciter.......................................................................... 4-1
4.1.1 Aural IF Synthesizer Board, 4.5 MHz ............................................... 4-1
4.1.2 Sync Tip Clamp/Modulator Board .................................................... 4-2
4.1.3 Delay Equalizer Board .................................................................. 4-6
4.1.4 IF Carrier Oven Oscillator Board ..................................................... 4-6
4.1.5 ALC Board, NTSC......................................................................... 4-7
4.1.6 IF Phase Corrector Board ............................................................ 4-13
4.1.7 VHF Mixer/Amplifier Enclosure Assembly ........................................ 4-15
4.1.8 Transmitter Control Board ........................................................... 4-17
4.1.9 Visual/Aural Metering Board......................................................... 4-22
4.1.10 Channel Oscillator Assembly, Dual Oven ....................................... 4-23
4.1.11 (Optional) EEPROM FSK Identifier Board....................................... 4-23
4.1.12 (Optional) IF Attenuator Board ................................................... 4-24
4.2 VHF High Band Amplifier Trays ............................................................. 4-24
CHAPTER 5 DETAILED ALIGNMENT PROCEDURES
5.1
5.2
5.3
5.4
5.5
5.6
VHF High Band Exciter Tray with Baseband Video and Audio Inputs........... 5-1
VHF Exciter Tray with 4.5-MHz Composite Input Kit ............................... 5-1
VHF Exciter Tray with Either Baseband or 4.5-MHz Composite Input .......... 5-2
IF Phase Corrector Adjustment .......................................................... 5-3
Linearity Corrector Adjustment .......................................................... 5-3
Phase and Gain Adjustment of the VHF Amplifier Trays........................... 5-4
430B, Rev. 0
1000 Watt VHF High Band Transmitter
Table of Contents
TABLE OF CONTENTS (continued)
5.7 Calibration of the Forward Output Power Level of the Transmitter ............. 5-5
5.8 Calibration of the Reflected Output Level of the Transmitter..................... 5-5
5.9 2-Way Combiner Assembly ............................................................... 5-6
5.10 Bandpass Filter Assemblies.............................................................. 5-6
5.11 VHF High Band Amplifier Tray .......................................................... 5-6
5.11.1 AGC Control Board ................................................................ 5-6
5.11.2 Phase Shifter Board............................................................... 5-7
5.11.3 VHF Filter/Amplifier Board ...................................................... 5-7
5.11.4 VHF High Band Amplifier Board ................................................ 5-7
5.11.5 Overdrive Protection Board ..................................................... 5-7
5.11.6 VHF High Band Amplifier Board ................................................ 5-7
5.11.7 3-Way Splitter Board ............................................................. 5-8
5.11.8 VHF High Band Amplifier Board ................................................ 5-8
5.11.9 3-Way Combiner Board .......................................................... 5-8
5.11.10 Calibration of the Visual Plus Aural Output
Power and VSWR Cutback..................................................... 5-8
5.12 Board Level Alignment Procedures .................................................... 5-9
5.12.1 (Optional) 4.5-MHz Composite Input Kit .................................... 5-9
5.12.2 Delay Equalizer Board ...........................................................5-10
5.12.3 (Optional) 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..............................................5-11
5.12.6 Sync Tip Clamp/Modulator Board ............................................5-11
5.12.7 Aural IF Synthesizer Board, 4.5 MHz ........................................5-13
5.12.8 ALC Board (Part 1 of 2).........................................................5-14
5.12.9 IF Phase Corrector Board.......................................................5-15
5.12.10 ALC Board, NTSC (Part 2 of 2) ..............................................5-15
5.12.11 Channel Oscillator Board, Dual Oven ......................................5-16
5.12.12 x4 Multiplier Board .............................................................5-16
5.12.13 VHF Filter/Mixer Board ........................................................5-16
5.12.14 VHF High Band Filter/Amplifier Board .....................................5-17
APPENDICES
APPENDIX A SYSTEM SPECIFICATIONS
APPENDIX B SAMPLE LOG REPORT SHEET & TYPICAL OPERATIONAL READINGS
APPENDIX C ASSEMBLY DRAWINGS
APPENDIX D SUBASSEMBLY DRAWINGS
430B, Rev. 0
ii
1000 Watt VHF High Band Transmitter
Table of Contents
LIST OF FIGURES
4-1
4-2
1 kW Minimum Ventilation Configuration ....................................... 4-4
Chassis Trak Cabinet Slides ........................................................ 4-5
5-1
Waveform ..............................................................................5-12
430B, Rev. 0
iii
1000 Watt VHF High Band Transmitter
Table of Contents
LIST OF TABLES
2-1
2-2
2-3
2-4
2-5
2-6
2-7
2-8
2-9
2-10
2-11
430B Major Trays and Assemblies ................................................ 2-1
VHF Exciter Tray Meters............................................................. 2-3
VHF Exciter Tray Switches .......................................................... 2-4
VHF Exciter Tray Fault Indicators ................................................. 2-4
VHF Exciter Tray Samples .......................................................... 2-5
VHF Amplifier Tray Switches ....................................................... 2-6
VHF Amplifier Tray Fault Indicators .............................................. 2-7
VHF Amplifier Tray Control Adjustments........................................ 2-7
VHF Amplifier Tray Sample ......................................................... 2-7
VHF Exciter Remote Interface Connections
With the A/V Input and Remote Interface Assembly .................... 2-8
VHF Amplifier Tray Remote Interface Connections
With the A/V Input and Remote Interface Assembly ...................2-10
3-1
VHF Amplifier Tray Boards and Assemblies ...................................3-25
5-1
5-2
Bandpass Filter Typical Values..................................................... 5-6
ALC Board LEDs ......................................................................5-14
430B, Rev. 0
iv
1000 Watt VHF High Band Transmitter
Chapter 1, Introduction
Chapter 1
Introduction
the appendices. Section titles in the text
for assembly or tray descriptions or
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.
1.1 Manual Overview
This manual explains the installation,
setup, alignment, and maintenance
procedures for the 430B 1000 Watt solid
state VHF high 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.
1.3 Safety
This instruction manual is divided into
five chapters and supporting appendices.
Chapter 1, Introduction, contains
information on the assembly numbering
system used in the manual, safety,
maintenance, return procedures, and
warranties. Chapter 2, System
Description, Maintenance and Remote
Interface Connections, describes the
transmitter and includes discussions on
system control and status indicators,
maintenance, and remote control
connections. Chapter 3, Installation and
Setup Procedures, describes 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 430B transmitter. Chapter
5, Detailed Alignment Procedures,
provides information on adjusting the
system to achieve peak operation of the
assemblies. The appendices contain
system specifications, a sample log
sheet, schematic, interconnects,
assembly and subassembly drawings and
parts list.
The VHF transmitters manufactured by
Axcera are designed to be easy to use
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 working on the transmitter.
Read All Instructions – All of the
operating and safety instructions should
be read and understood before operating
this equipment.
Retain Manuals – The manuals for the
transmitter should be retained at the
transmitter site for future reference. We
provide two sets of manuals for this
purpose; one set can be left at the office
while one set can be kept at the site.
Heed all Notes, Warnings, and
Cautions – All of the notes, warnings,
and cautions listed in this safety section
and throughout the manual must be
followed.
1.2 Assembly Designation Procedure
Axcera has assigned assembly numbers,
such as Ax (x=1,2,3…), to all assemblies,
trays, and boards that are referenced 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
430B, Rev. 0
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
1-1
1000 Watt VHF High Band Transmitter
Chapter 1, Introduction
aerosol cleaners. Use a damp cloth for
cleaning.
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#).
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.
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.
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 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
Technical Service Department if you have
any questions regarding service or
replacement parts.
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. In
addition, 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.
1.4 Contact Information
The Axcera Field Service Department can
be contacted by phone at (724) 8738100 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.
2.
3.
4.
When shipping an item to Axcera, please
include the MRA# on the packing list and
on the shipping container. The packing
slip should also include contact
information and a brief description of why
the unit is being returned.
What are the Customers’ Name and
call letters?
What are the model number and
type of transmitter?
How long has the transmitter been
on the air? (Approximately when
was the transmitter installed)
What are the symptoms being
exhibited by the transmitter?
Include current front panel meter
readings. If possible, include front
panel meter readings before the
problem occurred.
430B, Rev. 0
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.
1-2
1000 Watt VHF High Band Transmitter
Chapter 1, Introduction
Axcera can also be contacted through email at info@axcera.com and on the
Web at www.axcera.com.
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.
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.
Equipment furnished by Axcera, but not
bearing its trade name, shall bear no
warranties other than the special hoursof-use or other warranties extended by
or enforceable against the manufacturer
at the time of delivery to the buyer.
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
430B, Rev. 0
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.
1-3
1000 Watt VHF High Band Transmitter
Chapter 2, System Description,
Maintenance and Remote Interface Connections
Chapter 2
System Description, Maintenance
and Remote Interface Connections
The 430B is a complete 1000 watt VHF
high band solid state internally diplexed
television transmitter that operates at a
nominal visual output power of 1000
watts peak sync and an average aural
output power of 100 watts, at an A/V
ratio of 10 dB, 10% sound, or 50 watts
at 13 dB, 5% sound.
2.1 System Overview
The 430B is made up of the trays and
assemblies listed in Table 2-1.
Table 2-1. 430B Major Trays and Assemblies
MAJOR ASSEMBLY
DESIGNATOR
A2
A4
A6 and A7
A8
A12
TRAY/ASSEMBLY NAME
AC distribution panel
VHF exciter
Two VHF amplifier trays
VHF combiner assembly
Remote interface assembly
The (A4) VHF exciter can operate using
either the baseband audio and video
inputs alone or, if the (optional) 4.5-MHz
composite input kit is purchased, the 4.5MHz composite input or the baseband
video and audio inputs to produce a
diplexed, modulated, and on-channel
frequency visual + aural RF output. The
switching is accomplished by a relay on
the sync tip clamp modulator board that
uses a baseband select to control a relay
that selects either the 4.5 MHz generated
from the baseband inputs or from the
4.5-MHz composite input.
1265-1600
1070901
1301169
1219-1006
1083510
The RF output of the VHF exciter is split
two ways in (A5) the 2-way power
splitter assembly (ZFSC-2-2SMA). The
outputs of the splitter feed the two (A6
and A7) VHF high band amplifier trays
that amplify the RF signals to
approximately 600 watts pk. of sync
each. The outputs of the two VHF
amplifier trays are combined in (A8) a
VHF combiner assembly that provides
approximately 1050 watts peak of sync
output. The 1050 watt output is
connected to (A9) a bandpass filter
assembly. The bandpass filter is tuned to
provide the high out-of-band rejection of
unwanted products. The filter assembly
provides a forward and a reflected power
sample to the visual/aural metering
board 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
monitoring the system.
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.
430B, Rev. 0
DRAWING NUMBER
2-1
1000 Watt VHF High Band Transmitter
Chapter 2, System Description,
Maintenance and Remote Interface Connections
In the VHF amplifier tray, a forward
power sample and a reflected power
sample from the 3-way combiner board
are connected to the AGC Control Board
that peak-detects the samples and
connects them to the front panel meter
of the tray.
Operate, check that a dummy jumper
plug, with a jumper between pins 21 and
22, is connected to jack J9 on (A12) the
A/V input and remoter interface
assembly. This jumper provides the
interlock needed for the transmitter to
operate. If the interlock is present, the
green LED DS5, on the transmitter
control board, should be lit.
2.2 Control and Status
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 S2 is an Automatic/Manual switch
that controls the operation of the
transmitter using 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. With the system 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
(Loss; red LED DS9) and VSWR Cutback
(amber LED DS7).
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 two VHF amplifier
trays. In Operate, the green LED DS2 is
on and in Standby the amber LED DS1 is
on. NOTE: If the transmitter does not
switch to Operate when S1 is switched to
430B, Rev. 0
2-2
1000 Watt VHF High Band Transmitter
Chapter 2, System Description,
Maintenance and Remote Interface Connections
2.2.1 VHF Exciter Tray
Table 2-2. VHF Exciter Tray Meters
METER
Meter (A4-A18)
430B, Rev. 0
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 1000 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
Display
Position
Selects the desired ALC voltage
reading, % Exciter Power,
Switch S3, Meter
% Reflected Power, % Visual
Power, % Aural Power, video
level, or audio level.
Reads the audio level, ±25 kHz
balanced or ±75 kH composite,
on the 0 to 10 scale. Will
Audio
indicate baseband audio, if it is
(0 to 100 kHz)
connected to the transmitter,
even with the video + 4.5-MHz
SCA input selected.
ALC
Reads the ALC voltage level, .8
(0 to 10 volts)
VDC, on the 0 to 10 scale.
Reads the % Exciter Output
% Exciter
Power Level needed to attain
(0 to 120)
100% output of the transmitter
on the top scale.
Reads the % Aural Output
% Aural Power
Power of the transmitter,
(0 to 120)
100% = 100 watts at 10 dB
A/V ratio, on the top scale.
Reads the % Visual Output
% Visual Power
Power of the transmitter,
(0 to 120)
100% = 1000 watts peak of
sync, on the top scale.
% Reflected
Reads the % Reflected Output
(0 to 120)
Power, <5%, on the top scale.
Video
Reads the video level, at white,
(0 to 1 volt)
on the bottom 0 to 10 scale.
2-3
1000 Watt VHF High Band Transmitter
Chapter 2, System Description,
Maintenance and Remote Interface Connections
Table 2-3. VHF Exciter Tray Switches
SWITCH
Transmitter S1
Operate/Standby
Mode Select S2
Auto/Manual
Power Adjust (R1)
FUNCTION
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 two VHF amplifier trays. These
Enables will turn on the VHF amplifier trays. The opposite
occurs when the switch is turned to Standby.
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.
The 5 kΩ pot A20 sets the ALC level on the ALC board to set
the output power of the transmitter.
Table 2-4. VHF Exciter Tray Fault Indicators
INDICATOR
Video Loss (DS9 Red)
VSWR Cutback (DS7
Amber)
DESCRIPTION
Indicates that the input video to the transmitter has been
lost. The fault is generated on the ALC board in the VHF
exciter tray.
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 Front Panel Samples
SAMPLE
f(IF)
f(IC)
f(s)
Exciter O/P
Transmitter O/P
430B, Rev. 0
DESCRIPTION
A sample of the visual IF, 45.75MHz, that is taken from the
sample jack on the IF carrier oven oscillator board.
A sample of the intercarrier signal. 4.5MHz, that is taken
from the sample jack on the aural IF synthesizer board.
A sample of the channel oscillator output that is taken from
the sample jack of the channel oscillator assembly.
An output power sample of the exciter that is taken from
the VHF filter/amplifier board.
A forward power sample of the transmitter that is taken
from the visual/aural metering board.
2-4
1000 Watt VHF High Band Transmitter
Chapter 2, System Description,
Maintenance and Remote Interface Connections
2.2.2 VHF High Band Amplifier Tray
Table 2-6. VHF High Band Amplifier Tray Switches
SWITCH
On/Off Circuit Breaker CB1
Switch S1, Meter
Switch S2, Meter
430B, Rev. 0
FUNCTION
Switches 220 VAC through a 15 amp circuit breaker
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
Display
Position
Reads the % Forward Output
% Forward
Power of the tray (100%= 600
watts peak of sync + aural)
Reads the % Reflected Output
% Refl (Reflected)
Power (<10%)
Reads the AGC level of the tray
AGC Voltage
(1 to 2 VDC)
Reads the voltage from the
Power Supply
switching power supply
(+28 VDC)
Uses Switch S2 to indicate the
Current
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
Display
Position
Reads the current of (A4-A1)
the high band amplifier board
I1
(idling current=6 amps and
operating current=12 amps)
Reads the current of (A4-A2)
the high band amplifier board
I2
(idling current=6 amps and
operating current=12 amps)
Reads the current of (A4-A3)
the high band amplifier board
I3
(idling current=6 amps and
operating current=12 amps)
Reads the current of (A3-A2)
the high band driver board
I4
(idling current=3 amps and
operating current=6 amps)
2-5
1000 Watt VHF High Band Transmitter
Chapter 2, System Description,
Maintenance and Remote Interface Connections
Table 2-7. VHF High Band Amplifier Tray Fault Indicators
INDICATOR
Overdrive (DS1)
Enable (DS2)
Module Status (DS3)
VSWR Cutback (DS4)
Overtemp (DS5)
DESCRIPTION
Indicates that the level of drive is too high.
The protection circ uit will limit the drive
level to the set threshold. The fault is
generated on the overdrive protection
board.
Indicates that the Enable supplied by the
exciter tray is present
Indicates that the forward power sample
level is lower than the set reference level
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.
Indicates that the temperature of the
(A4-A5, A4-A6 or A5-A2) thermal switch is
above 175° F. When this fault occurs, the
Enable to the switching power supply is
immediately removed.
Table 2-8. VHF High Band Amplifier Tray Control Adjustments
ADJUSTMENT
Phase (A7-R2)
Gain (A6-R3)
DESCRIPTION
Adjusts the phase of the RF output by
approximately 70°
Adjusts the gain of the RF output when the
amplifier control board is in the AGC mode
Table 2-9. VHF High Band Amplifier Tray Sample
SAMPLE
RF Front Panel Sample
DESCRIPTION
Forward power sample of the tray from the
AGC control board
input kit, the baseband audio can remain
connected even if the 4.5-MHz composite
input kit is used, but the baseband video
must be disconnected from J2 and the
4.5-MHz composite input must be
connected to J2. The baseband select
command must be removed from J7-6
and J7-7.
2.3 Input Connections
The baseband video and audio inputs
alone or, if the (optional) 4.5-MHz
composite input kit is purchased, the 4.5MHz composite input or the baseband
video input and audio input to the
transmitter, connect to the A/V Input &
Remote Interface Assembly, mounted
facing the rear, at the top of the cabinet.
The baseband video input or the 4.5-MHz
composite input connects to jack J2. The
baseband balanced audio input connects
to TB1 or the composite, stereo, audio to
jack J3. To use the 4.5-MHz composite
430B, Rev. 0
2.4 AC Input to the Transmitter
The transmitter needs an AC input of 220
VAC at 40 amps connected to it in order
to operate. The 220 VAC input connects
to (A2) the AC distribution panel in the
2-6
1000 Watt VHF High Band Transmitter
Chapter 2, System Description,
Maintenance and Remote Interface Connections
upper middle facing the rear of the
cabinet. The panel contains the terminal
block TB1 to which the 220 VAC input
connects.
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 wandtype 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 silkscreened 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.
The AC distribution panel contains four
circuit breakers that supply the AC to the
rest of the transmitter. The input AC is
connected to the main AC circuit breaker
CB1 (40 amps) that distributes the 220
VAC to the terminal block TB2. TB2 has
three MOVs, VR1, VR2, and VR3,
mounted to the terminal block: VR1
across Line 1, VR3 across Line 2 and VR2
connected across the two legs. The input
AC is wired from TB2 through three
circuit breakers, CB2, CB3, and CB4, to
the rest of the transmitter. CB2 is a 10amp circuit breaker that supplies the AC
voltage to the IEC outlet strip (A2-A1)
that is connected into the VHF exciter,
the (optional) receiver tray, and any
other optional accessories. CB3 is a 20amp circuit breaker that supplies AC
through J5 to the (A6) VHF amplifier tray
#1. CB4 is a 20-amp circuit breaker that
supplies AC through J6 to the (A7) VHF
amplifier tray #2. When the VHF exciter
circuit breaker is switched on, +12 VDC
is supplied to the VHF amplifier trays for
the operation of the LED status indicators
in the tray.
It is recommended that the operating
parameters of the transmitter be
recorded from the meters on the trays
and the system metering control panel at
least once a month. It is suggested that
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.
2.5 Maintenance
2.6 Remote Interface Connections
The 430B is designed with components
that require little or no periodic
maintenance except for the routine
cleaning of the fans and the front panels
of the trays.
The remote interface connections listed in
Table 2-10 are made to the (A12) A/V
input and remote interface assembly,
mounted facing the rear near the top of
the cabinet. The remote connections are
made to jack J9, 37 pos “D” Conn., and
jack J10, 25 pos “D” Conn., on the
assembly. Refer to the transmitter
interconnect drawing (1303857) for
verification of the remote connections.
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
430B, Rev. 0
2-7
1000 Watt VHF High Band Transmitter
Chapter 2, System Description,
Maintenance and Remote Interface Connections
Table 2-10. 430B Remote Interface Connections to (A12) the A/V Input
and Remote Interface Assembly
FUNCTION
REMOTE JACK/PIN
NUMBER
Transmitter Enable Interlock
J9-21
Transmitter Enable Interlock
Rtn.
J9-22
INTERFACE TYPE
J9-21 and J9-22 must be
jumpered together for
normal operation. The
(1176-1038) jumper jack
should be used.
Remote Control Commands
Transmitter Standby
(Disable)
Transmitter
Standby/Operate Rtn.
Transmitter Operate
(Enable)
J9-9
Contact closure
J9-10
J9-11
Contact closure
Transmitter Manual
Transmitter Auto/Manual
Rtn.
Transmitter Auto
J9-15
Contact closure
J9-17
Contact closure
Power Level Raise (Optional)
Pwr Lvl Raise/Lower Rtn
(Optional)
Power Level Lower
(Optional)
J9-27
Contact closure
J9-29
Contact closure
Modulator Select (Optional)
Modulator Select Rtn
(Optional)
J9-31
Contact closure
J9-16
J9-28
J9-32
Remote Status Indications
Transmitter Operate
(Enable) Ind.
Operate/Standby Ind.
Return
Transmitter Standby
(Disable) Ind.
Transmitter Auto Indicator
Auto/Manual Indicator
Return
Transmitter Manual
Indicator
430B, Rev. 0
J9-12
50 mA max current sink
J9-13
J9-14
50 mA max current sink
J9-18
50 mA max current sink
J9-19
J9-20
2-8
50 mA max current sink
1000 Watt VHF High Band Transmitter
FUNCTION
VSWR Cutback Indicator
VSWR Cutback Indicator
Return
Chapter 2, System Description,
Maintenance and Remote Interface Connections
REMOTE JACK/PIN
NUMBER
J9-23
INTERFACE TYPE
50 mA max current sink
J9-24
Video Loss (Fault) Indicator
Video Loss (Fault) Ind. Rtn.
J9-25
J9-26
Receiver Fault (Optional)
J9-30
50 mA max current sink
Remote Metering
Visual Output Power
Visual Output Power Rtn
J9-1
J9-2
1V full scale at 1kΩ source
resistance
Aural Output Power
Aural Output Power Rtn
J9-3
J9-4
1V full scale at 1kΩ source
resistance
Reflected Power
Reflected Power Rtn
J9-5
J9-6
1V full scale at 1kΩ source
resistance
Exciter Output Power
Exciter Output Power Rtn
J9-7
J9-8
1V full scale at 1kΩ source
resistance
Forward Output Power (A6)
VHF High Band Amp
Forward Output Power (A6)
Rtn
Reflected O/P Power (A6)
VHF High Band Amp
Reflected O/P Power (A6)
Rtn
Forward Output Power (A7)
VHF High Band Amp
Forward Output Power (A7)
Rtn
Reflected O/P Power (A7)
VHF High Band Amp
Reflected O/P Power (A7)
Rtn
430B, Rev. 0
J10-1
J10-2
J10-3
J10-4
J10-6
J10-7
J10-8
J10-9
2-9
1V full scale at 1kΩ source
resistance
1V full scale at 1kΩ source
resistance
1V full scale at 1kΩ source
resistance
1V full scale at 1kΩ source
resistance
1000 Watt VHF High Band Transmitter
Chapter 3, Installation and Setup Procedures
Chapter 3
Installation and Setup Procedures
There are special considerations that
need to be taken into account before the
430B 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.
However, the closer the environment is
to this design, the greater the operating
capacity of the transmitter.
The fans and blowers 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 (700 watts) from the AC input
power (3800 watts). This number in
watts (3100) is then multiplied by 3.41,
which gives 10,571 BTUs that needs to
be removed every hour. 12,000 BTUs per
hour equals one ton, so a 1 ton air
conditioner will cool a 1000 watt
transmitter.
3.1 Site Considerations
The transmitter requires an AC input line
of 220 VAC with a rating of 40 amps for
the transmitter. Make sure that the
proposed site for the transmitter has the
necessary voltage requirements.
The 430B 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.
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.
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.
430B, Rev. 0
Now that the amount of heat that must
be removed is known, the next step is to
3-1
1000 Watt VHF High Band Transmitter
Chapter 3, Installation and Setup Procedures
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.
transmitter. Condensation may
occur on, or worse in, the
transmitter under certain
conditions.
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. For
tube type transmitters, this can be
especially serious if the
condensation forms in the tube
cavity and creates damaging arcs.
2.
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.
Do not have the air conditioner
blowing directly onto the
430B, Rev. 0
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:
The following precautions should be
observed regarding air conditioning
systems:
1.
3.
3-2
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
1000 Watt VHF High Band Transmitter
Chapter 3, Installation and Setup Procedures
not be carried in with the cooling
air.
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 filter area 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 neverexceed 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.
elevation. The free air delivery
method must not be used.
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 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
430B, Rev. 0
12.
Regular maintenance of the filters,
if used, can not be
overemphasized.
13.
Transmitters should not rely on
the internal blower to vent the
cooling air at elevations above
4000 feet. For external venting,
the air vent on the cabinet top
must be increased to an 8”
diameter for a 1kW transmitter.
An equivalent rectangular duct
may be used but, in all cases, the
outlet must be increased by 50%
through the outlet screen.
14.
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.
Axcera can be contacted at (724) 8738100.
3-3
1000 Watt VHF High Band Transmitter
Chapter 3, Installation and Setup Procedures
Figure 3-1. 1 kW Minimum Ventilation Configuration
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 ma ke
assembly of the transmitter much easier.
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 cabinets 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.
430B, Rev. 0
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 top and
the bottom of the VHF amplifier trays and
on the sides of the VHF exciter tray.
Inspect the trays for any loose hardware
or connectors, tightening as needed.
3-4
1000 Watt VHF High Band Transmitter
Chapter 3, Installation and Setup Procedures
Figure 3-2. Chassis Trak Cabinet Slides
Open the rear door. Inspect the interior
of the cabinet for packing materials and
carefully remove any packing materials
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.
3.4 Main AC Connection
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 all of the
circuit breakers associated with the
transmitter have been switched off.
3.3 Installing the Cabinets and Trays
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.
The main AC input circuit to the 1000
watt transmitter should be a 40-amp,
220 VAC line, using AWG 6 wire, inside of
a 1-1/4-inch conduit.
The 220 VAC input connections are made
to terminal block TB1, which is part of
the AC distribution panel, near the upper
right hand, rear portion of the cabinet.
The air intake to the 1000 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.
430B, Rev. 0
Connect Line 1 to TB1-1A, Line 2 to TB14A and chassis ground to TB1-3A.
The output of the bandpass filter
assembly, which is a “1-5/8” EIA
connector, should connect to the
transmission line for the antenna system.
This completes the unpacking and
installation of the 430B 1000 watt VHF
television transmitter. Refer to the setup
3-5
1000 Watt VHF High Band Transmitter
Chapter 3, Installation and Setup Procedures
and operation procedures that follow
before applying power to the transmitter.
approximately 7 seconds, the transmitter
will automatically revert to Standby and,
when the video signal is restored, the
transmitter will quickly return to Operate.
3.4 Setup and Operation
Initially, the transmitter should be turned
on with the RF output at (A9-A5-J2) the
bandpass filter assembly terminated into
a dummy load of at least 1000 watts. If a
load is not available, check that the
output of the bandpass filter assembly is
connected to the antenna.
Move the Operate/Standby switch on the
VHF exciter tray to Operate. Observe the
power supply reading, +28 V, on the
front panel of the VHF amplifier trays.
Note: If the transmitter does not switch
to Operate when the Operate/Standby
switch is placed in Operate, check that an
external interlock plug, with a jumper
wired from pins 21 to 22, is connected to
jack J9 on the (A12) A/V input and
remote interface assembly.
Connect the baseband balanced audio
input to the terminal block TB1 or the
composite audio input to BNC jack J6 on
the A/V input & remote interface
assembly, located facing the rear of the
cabinet near the top. The baseband
audio input can remain connected when
using the 4.5 MHz composite input
without affecting the operation of the
transmitter. Connect the baseband video
input to BNC jack J2 also on the A/V I/P
& 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 VHF exciter tray, look at the front
panel meter reading in the % Visual
Power position; it should read 100%. If
necessary, readjust the screwdriver
adjust power pot on the front panel of
the VHF exciter for 100%. As the power
level is being checked, observe the meter
reading in 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. Return the Operate/Standby
switch to Standby.
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. They should be very similar. 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.
Switch on the main AC, VHF exciter, and
the amplifier #1 and amplifier #2 circuit
breakers on the AC distribution panel
facing the rear of the cabinet and
mounted behind the rear door. On the
VHF exciter tray, switch the
Operate/Standby switch to Standby and
the Auto/Manual switch to Manual.
NOTE: Normal operation of the
transmitter is in Automatic. Automatic
operation uses the video input to the VHF
exciter as an Operate/Standby switch. In
Auto, if the input video is lost for
430B, Rev. 0
3-6
1000 Watt VHF High Band Transmitter
Chapter 3, Installation and Setup Procedures
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%.
100%. If necessary, adjust the power
screwdriver pot.
This completes the transmitter setup and
operation procedures for the 430B VHF
solid state 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.
If the transmitter is already connected to
the antenna, check that the output is
430B, Rev. 0
3-7
1000 Watt VHF High Band Transmitter
Chapter 4, Circuit Descriptions
Chapter 4
Circuit Descriptions
approximately 0 dBm, the mini-jumper
should be in the high gain position
between pins 1 and 2 of jack J11. If the
input level is approximately +10 dBm,
the mini-jumper should be in low gain
position between pins 2 and 3 of jack
J11. The balanced audio is then
connected to 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 (A4) VHF High Band Exciter
(1070901; Appendix C)
4.1.1 (A4) Aural IF Synthesizer
Board, 4.5 MHz (1265-1303;
Appendix D)
The aural IF synthesizer board amplifies
each of the three possible audio inputs
and connects them to a summing point
and amplifier circuit that provides the
single audio output. Either the balanced
audio or the composite stereo 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.
4.1.1.2 Composite Audio Input
The second possible audio input to the
board is the composite audio (stereo)
input at the BNC jacks J3 or J13. The two
jacks are loop-through connected; as a
result, the audio can be used in another
application by connecting the unused
jack and removing the jumper W4 from
J12. Jumper W4 on jack J12 provides a
75Ω input impedance when the jumper is
between pins 1 and 2 of jack J12 and a
high impedance when it is between pins
2 and 3. 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
applied to the differential amplifier U2C,
which eliminates common mode signals
(hum) on its input leads. The composite
input signal is then applied to 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.
4.1.1.1 Balanced Audio Input
The first of the three possible baseband
inputs to the board is a 600Ω-balanced
audio input. The balanced audio input
(+10 dBm) enters through jack J2, pins 1
(+), 2 (GND), and 3 (-) and is buffered
by U1B and U1C. The Diodes CR1 to CR4
protect the input stages of U1B and U1C
if an excessive signal level is present on
the input leads of jack J2. The outputs of
U1B and U1C are applied to differential
amplifier U1A, which eliminates any
common mode signals (hum) that may
be on its input leads. A pre-emphasis of
75 mS is provided by R11, C11, and R10
and can be eliminated by removing
jumper W5 on J5. The signal is then
applied to amplifier U1D whose gain is
controlled by jumper W3 on J11. Jumper
W3 on jack J11 is positioned according to
the input level of the audio signal (0 or
+10 dBm). If the input level is
430B, Rev. 0
4.1.1.3 Subcarrier Audio Input
The third possible input to the board is
the SCA input at BNC jack J4. The SCA
input has an input impedance of 75Ω that
can be eliminated by removing jumper
W2 from pins 1 and 2 of J14. The SCA
input is bandpass filtered by C66, C14,
R22, C15, C67, and R23 and is fed to the
buffer amplifier U3A. The amplified signal
4-1
1000 Watt VHF High Band Transmitter
Chapter 4, Circuit Descriptions
is then applied though the SCA gain pot
R24 to the summing point at pin 13 of
U2D.
4.5 MHz VCO IC U10; this sets up a
phase lock loop circuit. The 4.5 MHz VCO
will maintain the extremely accurate
4.5 MHz separation between the visual
and aural IF signals; any change in
frequency will be corrected by the AFC
error voltage.
4.1.1.4 Audio Modulation of the VCO
The balanced audio, or the comp osite
audio and/or the SCA buffered audio
signals, are fed to the common junction
of resistors R14, R20, and R27 that
connect to pin 13 of amplifier U2D. The
output audio signal at pin 14 of U2D is
typically .8 Vpk-pk at a ±25-kHz
deviation for balanced audio or .8 Vpk-pk
at ±75-kHz deviation for composite audio
as measured at TP1. This 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. This audio deviation level is
connected to the front panel meter
through the transmitter control board.
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.
The audio is connected to CR13 to CR16;
these 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 U5 PLL IC.
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.
4.1.1.6 Voltage Requirements
4.1.1.5 Phase Lock Loop (PLL) Circuit
4.1.2 (A5) Sync Tip Clamp/
Modulator Board (1265-1302;
Appendix D)
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
-12 VDC is connected to J1-5 and filtered
by L1, C1, and C2 before it is connected
to the rest of the board. +12 VDC is
connected to U8 and U9; these are 5 volt
regulator ICs that provide the voltage to
the U10 and U5 ICs.
A sample of the signal from the 4.5 MHz
aural VCO at the output of U11A is
applied to PLL IC U5 at the Fin
connection. In U5, the signal is divided
down to 50 kHz and is compared to a
50 kHz reference signal. The reference
signal is a divided-down sample of the
visual IF, 45.75 MHz signal that is applied
to the oscillator input connection on the
PLL chip through jack J6 on the board.
These two 50 kHz signals are compared
in the IC and the fV, and fR is applied to
the differential amplifier U3B. The output
of U3B is fed back through CR17 to the
430B, Rev. 0
The sync tip clamp/modulator board can
be divided into five separate 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 4.5 MHz
composite input that is connected to the
video input jack (either J1 or J2, which
are loop-through connected), and
4-2
1000 Watt VHF High Band Transmitter
Chapter 4, Circuit Descriptions
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 then
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.
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
(adjusted for 1 Vpk-pk at TP2) 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 to J6
on the sync tip clamp/modulator board.
The video from J6, pin 4, is then
connected through 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 the sync tip clamp
circuit.
4.1.2.1 Main Video Signal Path (Part 1 of
2)
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 jumper W4 is
on jack J3. With jumper W4 removed,
the input can be connected to another
transmitter through J1 that is loopthrough connected to J2.
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
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 voltagedivider network connected to U4A. If the
video level changes, the sample applied
to U4A changes. If 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; this will bring the sync tip level
back to approximately -1.04 VDC. Q7 will
be turned off and on according to 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 jumper W7 on J4
in the Auto Clamp -On position. U3 will
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 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
430B, Rev. 0
4-3
1000 Watt VHF High Band Transmitter
Chapter 4, Circuit Descriptions
increase or decrease its output, as
needed, to bring the peak of sync back to
the correct level as 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 adjustable
resistor R41 provides the manual clamp
bias adjustment for the video that
connects to Q2.
low-impedance, clamped video output at
pin 1.
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, that produces a video
output sample at J8-6 and 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; R48 adjusts the
sync stretch magnitude (amount) and
R45 adjusts the cut-in. This sync-stretch
adjustment should not be used to correct
for output sync problems, but it can be
used for video input sync problems. The
output of the sync-stretch circuit
connects to pin 5, the I input of mixer
Z1.
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
2. The clamp circuit is set by adjusting
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 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 peak of sync is
approximately -1.04 VDC as measured at
TP2.
The video signal is heterodyned in mixer
Z1 with the visual IF CW signal (45.75
MHz). The visual IF CW signal enters the
board at jack J15 and is connected to U9,
where it is amplified and wired to pin 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 nonlinearities generated by the mixer.
The modulated 45.75 MHz RF output of
mixer Z1 is amplified by U5 and is fed to
double-sideband visual IF output jack
J18. The level of this output jack is
adjusted by R70. J18 is the visual IF
loop-through output jack that is normally
jumpered 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.
4.1.2.3 Main Video Signal Path (Part 2 of
2)
The clamped video from Q2 is connected
to white clipper circuit Q3. Q3 is adjusted
with R20 and set to prevent video
transients from overmodulating the video
carrier. The clamped video is connected
to sync clipper circuit Q4 (adjusted by
R24); Q4 limits the sync to -40 IRE units.
The corrected video connects to emitter
follower Q4 whose output is wired to
unity gain amplifier U2A and provides a
430B, Rev. 0
After any external processing, the
modulated visual IF, double-sideband
signal re-enters the board through J19.
4-4
1000 Watt VHF High Band Transmitter
Chapter 4, Circuit Descriptions
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, and
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
can be adjusted to set the visual IF gain;
this is the amount of visual IF signal that
is coupled to amplifier IC U8. R63 and
C30 are adjusted for the best VSBF
frequency response. The amplified IF
signal 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 test point TP5.
that is fed to jack J16, the 41.25 MHz
loop-through out jack of the board.
For normal operation, the 41.25 MHz
signal is jumpered by a coaxial cable
from J16 to J17 on the board. If the
(optional) aural IF loop-through kit is
purchased, the 41.25 MHz signal is
connected to the rear of the tray, to
which any 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 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 41.25 MHz that
sets the A/V ratio for the diplexer circuit.
The diplexer circuit takes the modulated
45.75 MHz visual IF and the modulated
aural IF 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 combined IF output jack J20 on the
board. A sample of the combined IF
output is provided at J21 on the board. If
a 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.
4.1.2.5 41.25 MHz Aural IF Circuit
On this board, the 41.25 MHz aural IF is
created by mixing the modulated
4.5 MHz aural intercarrier signal,
produced by the aural IF synthesizer
board or from the composite 4.5 MHz
filter board, with the 45.75 MHz CW
signal produced by the 45.75 MHz IF
carrier oven oscillator board. The
modulated 4.5 MHz aural intercarrier
signal enters the board at J14 or J28 and
is connected to IF relay K1. Jumper W3
on J7 determines whether the 4.5 MHz
used by the board is internally generated
or from an external source. With 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 mixer Z2. If an
external 4.5 MHz signal is used, it enters
the board at J12 and is fed through gain
pot R88 to amplifier IC U13A. The
amplified 4.5 MHz is then connected to J7
and, if jumper W3 is between pins 1 and
2, the 4.5 MHz signal from the external
source is connected to the mixer. 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.
4.1.2.6 Operational Voltages
The +12 VDC needed to operate the
transmitter control board enters the
board at J23, pin 3, and is filtered by
L26, L33, and C73 before it is fed 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.
The output of the mixer is fed to a
bandpass filter that is tuned to pass only
the modulated 41.25 MHz aural IF signal
430B, Rev. 0
4-5
1000 Watt VHF High Band Transmitter
Chapter 4, Circuit Descriptions
4.1.3 (A6) Delay Equalizer Board
(1227-1204; Appendix D)
4.1.4 (A7) IF Carrier Oven Oscillator
Board (1191-1404; Appendix D)
The delay equalizer board provides a
delay to the video signal, correction to
the frequency response, and
amplification of the video signal.
The IF carrier oven oscillator board
generates the visual IF CW signal at
45.75 MHz for NTSC system "M" usage.
The +12 VDC is applied through jack J10
to crystal oven HR1, which is preset to
operate at 60° C. The oven encloses
crystal Y1 and stabilizes the crystal
temperature. The crystal is the principal
device that determines the operating
frequency and is the most sensitive in
terms of temperature stability.
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
amplifier stage U1; the gain is controlled
by R29. The video output of the amplifier
stage is wired to the first of four delayequalizing 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 this FCC
specification and should not be
readjusted without the proper
equipment.
Crystal Y1 operates in an oscillator circuit
consisting of transistor Q1 and its
associated components. Feedback is
provided through a capacitor-voltage
divider, consisting of C5 and C6, that
connects to the crystal mounted in a
common-base amplifier configuration
using Q1. The operating frequency of the
oscillator can be adjusted by variable
capacitor C17. The oscillator circuit
around Q1 has a separate regulated
voltage, +6.8 VDC, which is produced by
a combination of dropping resistor R4
and 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,
keeps the oscillator from being loaded
down by Q2.
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
is attained. The delay-equalized video
signal is connected to J1-4, the video
output of the board. A sample of the
delayed video signal is connected to J2
on the board and can be used for testing
purposes.
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 through C11 to J3, the main
output jack. This 45.75 MHz signal is at
about the +5 dBm power level. In most
systems, this output is either directed to
a visual modulator board or to some
splitting and amplifying arrangement that
distributes the visual IF carrier for other
needs. The second output from the
collector of Q2 is fed to the base of Q4,
the emitter follower transistor.
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.
430B, Rev. 0
4-6
1000 Watt VHF High Band Transmitter
Chapter 4, Circuit Descriptions
Q4 drives two different output circuits.
One output is directed through voltage
dividers R14 and R15 to jack J2 that can
connect 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 at a power level of
approximately -2 dBm, which is sufficient
to drive most frequency counters. The
other output of Q4 connects to 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. This 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 of this is when the PLL circuit
uses the aural IF synthesizer board and
the aural VCO. 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.
the board to control the output power of
the transmitter.
The visual + aural IF input signal,
(0 dBm), from the modulator 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 the
receiver IF input jack J1. The modulator
IF input connects to relay K3 and the
receiver IF input connects to relay K4.
The two relays are controlled by the
Modulator Select command that is
connected to J30 on the board. Modulator
select enable/disable jumper W11 on J29
controls whether the Modulator Select
command at J30 controls the operation of
the relays or not. With jumper W11 on
J29, pins 1 and 2, the Modulator Select
command at J30 controls the operation of
the relays; with jumper W11 on J29, pins
2 and 3, the modulator is selected all of
the time. This is the normal position.
4.1.5.1 Modulator Selected
With the modulator selected, J9-31 &
J9-32 located on the A/V I/P & Remote
Interface Assembly are connected
together; this makes J30 low and causes
relays K3 and K4 to de-energize. When
K4 is de-energized, it connects the
receiver IF input at J1, if present, to 50Ù.
When K3 is de-energized, it connects the
modulator IF input at J32 to the rest of
the board; Modulator Enable LED DS5
will be illuminated.
The stages U1, U2, Q5, and Q6 are
powered by +5.1 VDC, which is obtained
using the +12 VDC line voltage, the
voltage-dropping resistor R16 and the
Zener diode VR2.
The +12 VDC power is applied to the
board through jack J4, pin 3, and is
isolated from the RF signals that may
occur in the +12 VDC line through the
use of RF choke L2 and filter capacitor
C10.
4.1.5.2 (Optional) Receiver Selected
With the (Optional) receiver selected,
which is J9-31 & J9-32 located on the
(A12) A/V I/P & Remote Interface
Assembly (connected to J30 on the
board), not connected together, relays
K3 and K4 are energized. When K4 is
energized, it connects the receiver IF
input at J1, if present, to the rest of the
board. When K3 is energized, it connects
to the modulator IF input at J32 to 50Ù.
The Modulator Enable LED DS5 will be
illuminated.
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
430B, Rev. 0
4-7
1000 Watt VHF High Band Transmitter
Chapter 4, Circuit Descriptions
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. Without
the threshold detector, and with the pindiode attenuator at minimum, when the
signal is restored it will overdrive the
stages following this board.
4.1.5.3 Main IF Signal Path (Part 1 of 3)
The selected visual + aural IF input (0
dBm) signal is split, with one half of the
signal 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.
As part of the threshold detector
operation, the minimum IF input level at
TP3 is fed through detector CR15 to opamp 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 and
through red LED DS1, the input level
fault indicator, which becomes lit, resistor
R54, and transistor Q2 to +12 VDC. The
high from U9A also connects through
diode CR16 to U9B, pin 5, whose output
at pin 7 goes high. The high connects
through range adjust pot R74 to J20,
which connects to the front panelmounted power adjust pot. This high
connects to U10A, pin 2, and causes it to
go low at output U10A, pin 1. The low is
applied through jumper W3 on J6 to the
pin-diode attenuator circuit that cuts
back the IF level and, therefore, the
output power level, to 0. When the input
signal level increases above the threshold
level, the output power will raise, as the
input level increases, until normal output
power is reached.
4.1.5.4 Input Level Detector Circuit
The other part of the split IF input is
connected through L2 and C44 to U7; U7
is an IC amplifier that is the input to the
input level detector circuit. The amplified
IF is fed to T4; T4 is a step-up
transformer that feeds 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
emitter follower Q1. The signal is then
connected to detector CR15 to produce a
peak-sync voltage that is applied to opamp 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 video input level at TP3 is also fed to
a sync-separator circuit, consisting of IC
U8, CR17, Q3, and associated
components, and then to a comparator
circuit made up of U9C and U9D. The
reference voltage for the comparators is
determined by a voltage divider
consisting of R129, R64, R65, R66, and
R130 (off the -12 VDC line). When the
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. The ALC,
430B, Rev. 0
4-8
1000 Watt VHF High Band Transmitter
Chapter 4, Circuit Descriptions
input signal level to the detector at TP3
falls below this reference threshold,
which acts as a loss of sync detector
circuit, the output of U9C and U9D goes
towards the -12 VDC rail and is split, with
one part biasing on transistor Q5. A
current path is then established from the
+12 VDC line through Q5, the resistors
R69, R137, and the red LED DS3 (video
loss indicator), which becomes lit. When
Q5 is 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.
pins 1 and 2, or from pot R87 when the
jumper is in the Manual Gain position.
On 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 changes 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, 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 lowvalue resistor. In addition, the larger
current flow increases the voltage drop
across R9 that tends to turn off 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, and through R5, CR1,
CR2, and R9, biases series element CR3
off and 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
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.
The other low output of U9C and U9D is
connected through CR20 to jack J5.
Jumper W2 on J5, in the Cutback Enable
position (between pins 2 and 3),
connects the low to the base of the
forward-biased Q4. If 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 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 pindiode attenuator to cut back the level of
the output to approximately 25%.
4.1.5.5 Pin-Diode Attenuator Circuit
The input IF signal is fed to a pin-diode
attenuator circuit that consists of CR1 to
CR3. Each of the pin diodes contain a
wide intrinsic region; this makes the
diodes function as voltage-variable
resistors at this intermediate frequency.
The value of the resistance is controlled
by the DC bias supplied to the diode. 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
430B, Rev. 0
4.1.5.6 Main IF Signal Path (Part 2 of 3)
When the IF signal passes out of the pindiode attenuator through C11, it is
applied to modular amplifier U1. This
device includes within it the biasing and
impedance matching circuits that makes
it operate as a wide-band IF amplifier.
4-9
1000 Watt VHF High Band Transmitter
Chapter 4, Circuit Descriptions
The output of U1 is available, as a
sample of the pre-correction IF for
troubleshooting purposes and system
setup, at jack J2. The IF signal is then
connected to the linearity corrector
portion of the board.
corrector is set by controlling where CR4
and CR5 turn on. This is accomplished by
adjusting cut-in resistor R34; R34 forms
a voltage-divider network from +6.8 VDC
to ground. The voltage at the wiper arm
of R34 is buffered by unity-gain amplifier
U5D. This reference voltage 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
unity-gain amplifier U5B. The reference
voltage is then connected to diode CR5
through choke L11. The two chokes L11
and L12 form a high impedance for RF
that serves to isolate the op-amp ICs
from the IF.
4.1.5.7 Linearity Corrector Circuits
The linearity corrector circuits use three
stages of correction to correct for any
amplitude non-linearities of 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 circuits. Zener diode VR1,
with R33 and R135, provides a +6.8 VDC
reference and the diodes CR11 and CR12
provide a .9 VDC reference that
temperature compensates for the two
diodes in each corrector stage.
For the linearity correctors to operate, 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 determined by the
adjustment of R13). The signal is next
applied to amplifier U2 to compensate for
the loss through the L-pad. The
breakpoint, or cut-in point, for the first
430B, Rev. 0
After the signal is amplified by U2, it is
applied to the second corrector stage
through T2. This corrector and the third
corrector operate in the same fashion as
the first. All three corrector stages are
independent and do not interact with
each other.
The correctors can be disabled by moving
jumper W1 on J4 to the Disable position,
between pins 2 and 3; this moves all of
the breakpoints past the tip of sync so
that they will have no affect. The IF
signal exits the board at IF output jack J3
after passing through the three corrector
stages and is normally connected to an
external IF phase corrector board.
4.1.5.8 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. The IF then passes through a
bandpass filter consisting of L20, C97,
C62, L21, C63, L22, L23, C64, and C99.
This bandpass filter is identical in both
form and function to the one described in
Section 3.3 of this chapter. In this case,
the 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.
4-10
1000 Watt VHF High Band Transmitter
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 IF signal is split off and
connected the IF sample jack J10. The
IF connects to jacks J27 and J28. These
jacks control whether a 6 dB pad is
included in the circuit by the positioning
of jumpers W9 and W10. The 6 dB pad-in
is when jumpers W9 and W10 are
connected between pins 2 and 3 on J27
and J28. The 6 dB pad-out is when
jumpers W9 and W10 are connected
between pins 1 and 2 on J27 and J28.
Normally, the pad is out. The IF signal is
then applied to a two-stage, frequencyresponse corrector circuit that is adjusted
as needed.
Variable resistors R103 and R106 adjust
the depth and gain of the notches and
variable caps C71 and C72 adjust the
frequency position of the notches. The IF
signal is amplified by U13 and U14 before
it is connected to J12, the IF output jack
of the board. R99 is an output level
adjustment that is set to provide
approximately 0 dBm of IF output at J12.
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.
4.1.5.9 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 is
between pins 1 and 2 and jumper W8 on
J9 is between pins 1 and 2. The IF signal
is applied to transformer T5; T5 doubles
the voltage swing by means of a 1:4
impedance transformation before it is
430B, Rev. 0
Chapter 4, Circuit Descriptions
connected to the ALC detector circuit on
the board and amplified by U10B.
For normal operation, jumper W7 on J26
is between pins 1 and 2 and jumper W5
on J21 is 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
achieved, if the (optional) remote power
raise/lower kit (1227-1039) is purchased,
by R75, a motor-driven pot controlled by
switch S1 on the board, or screwdriver
adjust pot R1 on the front panel of the
UHF exciter tray. An external power
raise/lower switch can be used by
connecting it to jack J9, at J9-27 power
raise, J9-28 power raise/lower return,
and J9-29 power lower, on (A12) the A/V
I/P & Remote Interface Assembly. S1, or
the remote switch, controls relays K1 and
K2, which control 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 UHF 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.
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 pindiode attenuator circuit. If there is a loss
of gain somewhere in an IF circuit, the
output power of the transmitter will drop.
The ALC circuit senses this drop at U10A
and automatically lowers the loss of the
pin-diode attenuator circuit to
compensate by increasing the gain.
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 resistor
R77 to a summing point at op-amp
U10A, pin 2. The current available from
4-11
1000 Watt VHF High Band Transmitter
the ALC detector is offset, or
complemented, by 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 IF input jack
J7 of this board should drop in level,
which normally means that the output
power is decreasing, the null condition
would no longer occur at U10A, pin 2.
When the level drops, the output of
U10A, 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 and increase the IF
level; this will act to compensate for the
decrease in level. If the ALC cannot
increase the input level enough to satisfy
the ALC loop, because of 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.
4.1.5.10 Scrambled Operation with
Encoding
For encoded, scrambled operation,
jumper W4 on J8 must be connected
between pins 2 and 3, jumper W8 on J9
must be between pins 3 and 2, jumper
W7 on J26 must be between pins 2 and
3, and jumper W5 on J21 must be
between pins 2 and 3. The IF is
connected through W4 on J8 to the sync
regeneration circuits.
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 connects 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
430B, Rev. 0
Chapter 4, Circuit Descriptions
of U15A is peak detected by CR26 and
fed to U15B. If necessary, intercarrier
notch L39 can be placed in the circuit by
placing W6 on J22. The intercarrier notch
is adjusted to filter any aural and 4.5MHz 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.
4.1.5.11 Fault Command
The ALC board also has circuitry for an
external mute fault input at J19, pin 6.
This is a Mute command and, 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 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.
4-12
1000 Watt VHF High Band Transmitter
This establishes a very fast muting
action, by reverse biasing CR3, in the
event of an external VSWR fault.
4.1.5.12 ±12 VDC Needed to Operate the
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.
The +12 VDC also connects to U16, a 5VDC regulator IC, that produces the +5
VDC needed to operate 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 output amplifier devices such as
Klystron power tubes and solid-state
amplifiers. Two separate, adjustable IF
paths are 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 inphase IF. When they are combined in Z1,
it provides the required adjustable phase
correction to the IF signal.
The IF input signal 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 coaxial cable W4 to
jack J6, the quadrature input on the
board. The IF output 2 at J3, is
jumpered through coaxial cable W5 to
jack J7, the in-phase input on the board.
4.1.6.1 Phase Corrector Circuit
The phase corrector circuit corrects for
any amplitude nonlinearities of the IF
signal. It is designed to work at IF and
430B, Rev. 0
Chapter 4, Circuit Descriptions
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 increase either above or below the
threshold, and either black or white
stretch can be achieved.
In the phase corrector circuit, the IF
signal from J6 is applied to transformer
T1; T1 doubles the voltage swing using a
1:4 impedance transformation. Resistors
R8, R61, R9, and R48 form an L-pad that
attenuates 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 and allow current to flow through
R7. When R7 is put in parallel with the Lpad, the attenuation through the L-pad is
lowered, causing black stretch.
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 from the +12 VDC line. Diodes
CR11 and CR12 provide a .9 VDC
reference to temperature compensate
the corrector circuits from the effects of
the two diodes in each corrector stage.
The threshold for the first corrector stage
is set by controlling where the diodes
CR1 and CR2 turn on. This is
accomplished by adjusting R3 to form 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. The .9 VDC reference is
connected to U9D, a unity-gain amplifier,
whose output is wired to CR2. These two
references are connected to diodes CR1
and CR2 through chokes L2 and L3. The
two chokes form a high impedance for RF
to isolate the op-amps from the RF. The
adjusted signal is next applied to
4-13
1000 Watt VHF High Band Transmitter
amplifier U2 to compensate 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 T2 and then to a third corrector
stage through T3. The other two
corrector stages operate in the same
manner as the first; they are
independent and do not interact with
each other.
When jumper W1 on J8 is connected
from 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 center pin 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 by
controlling the attenuation through the
path.
The phase correctors can be bypassed by
moving jumper W2 on J9 to the Disable
position. This action will move all of the
threshold points past sync tip so that
they will have no effect. R68 can be
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
The amplitude corrector circuit 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 +6.8
430B, Rev. 0
Chapter 4, Circuit Descriptions
VDC and the diodes CR11 and CR12
provide a .9 VDC reference voltage to
temperature compensate for the two
diodes 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
The amount of stretch is determined by
the adjustment of R35.
The signal is next applied to 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 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 unitygain amplifier U8A. C36 keeps the
reference from sagging during the
vertical interval. The reference voltage is
then connected to 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 IF.
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 lowers the
level of the signal. The signal is applied
to amplifier U6 to compensate for the
4-14
1000 Watt VHF High Band Transmitter
loss in level through the L-pad. 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 to
lower the level of the signal. The signal is
applied to amplifier U7 to compensate for
the loss in level through the L-pad. TP1 is
a test point that gives the operator a
place to measure the level of the inphase IF signal that is connected to
mixer stage Z2. The amplitude corrector
can be disabled by moving the jumper
W3 on J10, to the Disable position. This
will move the breakpoint past sync tip
and will have no effect on the signal.
4.1.6.3 Output Circuit
The phase-corrected signal from pin 1 on
combiner Z2 exits the board at the IF
output jack J4, after passing through a
matching network consisting of six
resistors.
4.1.7 (A11) VHF Mixer/Amplifier
Enclosure Assembly (1088067;
Appendix C)
The VHF mixer/amplifier enclosure
assembly is made up of the x4 multiplier
board, the VHF filter/mixer board, and
the VHF high band filter/amplifier board.
4.1.7.1 (A11-A1) x4 Multiplier Board
(1174-1112; Appendix D)
The x4 multiplier board multiplies the
frequency of an RF input signal by a
factor of four. The board is made up of
two identical x2 broadband frequency
doublers.
The input signal (+5 dBm) at the
fundamental frequency enters through
SMA jack J1 and is fed through a 3 dB
matching pad, consisting of R1, R2, and
R3, to amplifier IC U1. The output of the
amplifier stage is directed through a
bandpass filter, consisting of L2 and C4,
that is tuned to the fundamental
frequency. The voltage measured at TP1
430B, Rev. 0
Chapter 4, Circuit Descriptions
is typically +0.6 VDC. The first doubler
stage consists of Z1 with bandpass filter
L3 and C6 tuned to the second harmonic.
The harmonic is amplified by U2 and fed
through a bandpass filter, consisting of
C10 and L5, also tuned to the second
harmonic frequency. The voltage
measured at TP2 is typically +1.2 VDC.
The next doubler stage consists of Z2
with bandpass filter C12 and L6 tuned to
the fourth harmonic of the fundamental
frequency. The fourth harmonic is then
amplified by U3 and fed to the SMA
output jack of the board at J2. The
typical LO signal output level is a nominal
+15 dBm.
The +12 VDC for the board enters
through jack J3-3 and is filtered by L7
and C16 before being distributed to the
circuits on the board.
4.1.7.2 (A11-A2) VHF Filter/Mixer
Board (1150-1102; 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 board is
mounted inside of (A11) the VHF
mixer/amplifier enclosure assembly
(1088067), an aluminum enclosure that
provides RFI protection. The
filter/amplifier board (1064252) is also
mounted inside the enclosure.
The LO input (+5 dBm) connects to the
board at J3 and is fed to a filter circuit.
The input to the filter consists of C11,
C12, and L5, with C12 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. Capacitor C15 is
adjusted for the best coupling. The
filtered LO is amplified by U2 and
connected to LO output jack J4. Typically,
the output at jack J4 is jumpered by a
coaxial jumper to jack J5 on the board.
The LO at J5 connects to mixer Z1 at pin
1 (+14 dBm).
4-15
1000 Watt VHF High Band Transmitter
The IF input connects to the board at J7
and is fed to mixer Z1 at pin 3 (-3 dBm).
Mixer Z1 takes the LO input at pin 1 and
the IF input at pin 3 to produce an RF
output at pin 8. The RF output at pin 8
(-14 dBm) connects through a pi-type
attenuator, made up of R3, R4, and R5,
before it is connected to RF output jack
J6. Normally, jack J6 is connected by a
coaxial jumper to J1 on the board. J1
connects 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 center frequency, 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).
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 (A11-A3) VHF High Band
Filter/Amplifier Board (1064252;
Appendix D)
The VHF high 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
and is fed through a channel filter circuit.
The input to the filter consists of 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; J6 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,
430B, Rev. 0
Chapter 4, Circuit Descriptions
R2, and R3, before it is wired to a pindiode attenuator circuit. The pin-diode
attenuator circuit is made up of CR1,
CR2, and CR3 and is controlled by the
bias current applied 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 the 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
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 2 and 3 is auto gain, which uses
the external control voltage input to jack
J4 as the level control. NOTE: This
arrangement is not used in this
configuration.
The level-controlled RF is pre-amplified
by U1 and connected to Q1, the output
amplifier for the board. C17 is used to
maximize the RF signal. The RF output is
amplified by Q1 and applied to the RF
output jack for the board at J2.
The output from Q1 is first fed through
direction coupler Z1 before exiting the
board at J2, the RF output. The RF
sample derived from Z1 has two
functions. The first function is to provide
an RF sample at J8 on the board that is
fed to the front panel of the exciter tray
through a voltage divider consisting of
R19 and R18. The second function is to
provide a peak-detected voltage that is
used by the exciter tray for metering
purposes. The sample provided by Z1,
pin 3, is first fed through a dB 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 C14 before being
buffered and amplified by U2. The peakdetected voltage that is used for
metering purposes is controlled by pot
R28 on the board.
4-16
1000 Watt VHF High Band Transmitter
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 from the rest of the
tray by L5 and C19 before being applied
to the entire board. The –12 VDC enters
the board at J3, pin 5, and is filtered and
isolated from the rest of the tray by L6
and C35 before being applied to the
entire board.
4.1.8 (A17) Transmitter Control
Board (1265-1311; Appendix D)
The transmitter control board provides
information on system control functions
and the operational LED indications;
these can be viewed on the front panel of
the transmitter. The main control
functions are for the Operate/Standby
and Auto/Manual selections. When the
transmitter is switched to Operate, the
board supplies the enables to any
external 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
Auto.
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
and, 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,
one coil 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
430B, Rev. 0
Chapter 4, Circuit Descriptions
fault, lows will also be applied to U4B-10,
U4B-11, and U4B-12.
With all the low inputs to U4B, the output
at U4B-13 will be low. The low biases off
Q1 and this turns off the amber Standby
LED DS1 on the front panel. In addition,
this action applies a high to Q2 and 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 and
biases it off; this allows the ALC to be
applied to J1 and connect to any external
amplifier trays. The low from U4B-13 is
also applied to Q4 and Q24, which are
biased off, and removes the disables
from J1-4 and J18-1. The low from U4B13 also connects to Q10, which is biased
on, and connects a high to Q6, Q7, Q8,
and Q9; these are biased on and apply
-12 VDC enables to J8-2, J8-3, J8-4, and
J8-5, which connect to any external
amplifier trays. The high applied to Q2 is
also connected to Q5 and Q26, which are
biased on, and apply a low enable to J13, which connects to a remote operate
indicator. The transmitter is now in the
Operate mode.
When the Operate/Standby switch S1 is
moved to Standby, the other coil 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 and applies a low to
the amber Standby LED DS1, on the
front panel, and turns on and applies a
low to Q2. This causes Q2 to turn off and
extinguishes the green Operate LED DS2.
When Q12 is biased on, the output from
U2C goes low and pulls the ALC voltages
at J1 low; this lowers the gain of the
external amplifier trays. The high from
U4B-13 is applied to Q4 and Q24, which
are biased on, and applies disables at J14 and J18-1. The high from U4B-13
connects to Q10, which is biased off. The
Q10 bias off removes the high from Q6,
Q7, Q8, and Q9, which are biased off,
and removes the -12 VDC enables at J82, J8-3, J8-4, and J8-5, which connect to
the external amplifier trays. The low
4-17
1000 Watt VHF High Band Transmitter
applied to Q2 is also connected to Q5 and
Q26, which are biased off, and removes
the remote enable at J1-3. 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 Auto/
Manual switch S2 located on the front
panel of the 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 Operate/Standby switch
S1 is moved to Standby. With S2 in Auto,
a low is applied to one coil in the relay
and this energizes and closes the
contacts. The closed contacts apply a low
to the green Automatic LED DS3; as a
result, DS3 is illuminated. The low from
the relay connects to U5A, pin 2; U5D,
pin 13; Q21; and Q23. When Q21 and
Q23 are biased off, this 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 to
Q22, biasing it on. The drain of Q22 goes
low and is applied to J8-7; this enables
any remote auto indicator connected to
J8-7. The low to Q23 biases it off and
removes the enable to any remote
manual indicator connected to J8-6.
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
other coil in the relay and this energizes
and opens the contacts. The open
contacts remove the low from the green
Automatic LED DS3 on the front panel
and causes it to extinguish. The high
connects to U5A, pin 2; U5D, pin 13;
Q21; and Q23. Q21 and Q23 are biased
on; this 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
430B, Rev. 0
Chapter 4, Circuit Descriptions
to J8-7; this will disable any remote auto
indicators connected to it J8-7. Q23 is
biased on and applies a low enable to any
remote manual indicator connected to J86.
4.1.8.3 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 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, and to
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
4-18
1000 Watt VHF High Band Transmitter
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,
and to U5A, pin 1. With 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, is 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, video loss
fault, VSWR cutback fault,
overtemperature fault, and ALC fault,
which may occur in the transmitter and
are applied to the transmitter control
board. 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 external (A8)
combiner assembly.
4.1.8.5 Video Loss Fault
If a video loss occurs while the
transmitter is in Auto, the system will
change to the Standby mode until the
video is returned; at that point, it 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 board.
With jumper W1 in place on J10, the
video fault is connected to 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
430B, Rev. 0
Chapter 4, Circuit Descriptions
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, and, 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 high at
U5C, pins 8 and 9, causes its output at
pin 10 to go low. This low is connected to
U5D, pin 12, and, if the transmitter is in
Auto, pin 13 of U5D is also low. The lows
on pins 12 and 13 cause the output to go
high and forward bias Q19. The drain of
Q19 goes low and connects the coil 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 connects to the
operate coil 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.
4-19
1000 Watt VHF High Band Transmitter
4.1.8.6 Overtemperature Fault
In this 1 kW VHF transmitter the (A8-A1)
thermal switch mounted on the (A8)
Combiner Assembly connects to J11-1 &
J11-35 on the rear of the VHF Exciter.
These connect to J8-1 & J8-35 on the
Transmitter Control Board. If the
temperature of the thermal switch rises
above 170° F, it closes and applies a low
to J8-1. The low connects to Q3, which
is biased off, and to the red
Overtemperature LED DS6, which is
biased on. The drain of Q3 goes high
and connects to pins 11 and 12 of U4B.
The high at the input to U4B causes it to
go high and switches the Transmitter to
Standby. This also removes the Operate
Enable commands to the two external
VHF amplifier trays.
4.1.8.7 VSWR Cutback Fault
The reflected power sample of the RF
output of the transmitter 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;
J1-5 is wired to J10-5 on the rear of the
tray for remote monitoring. Another splitreflected 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 the 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, J18, and J1-9. These are ALC outputs to
the 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 bias-adjust pot that sets
the level of the pin attenuator bias
available as an output at J16. The high at
430B, Rev. 0
Chapter 4, Circuit Descriptions
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 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, and
produces a low at output pin 4. The low
is wired to Q18, which is biased off, and
this makes its drain go high. The high
connects to U3D, pin 12 and, because
the level is above the preset, the output
4-20
1000 Watt VHF High Band Transmitter
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 that are controlled by S3. They
are Audio level, Video level, % Aural
Power, % Visual Power, % Reflected
Power, % Exciter Power, and ALC
voltage. The video sample connects to
the board at J5-4 and is connected
through video calibration pot R20 to
position 6 on front panel meter switch
S3. The 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. The 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 S3. The visual
sample connects to the board at J2-5 and
is connected through buffer amplifier
U1D and 100Ω resistor R86 to position 4
on front panel meter switch S3. 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 front panel meter switch S3. The
exciter sample connects to the board at
J2-3 and is connected through buffer
amplifier U1A and 100Ω resistor R87 to
position 2 on front panel meter switch
S3. The ALC sample connects to the
board at J6-1 and is connected through
buffer amplifier U2C and ALC calibration
pot R15 (which adjusts the output of
U2A, pin 1) and through 100Ω resistor
R18 to position 1 on front panel meter
switch S3. Typical readings on the meter
are:
430B, Rev. 0
Chapter 4, Circuit Descriptions
•
•
•
•
•
Video = 1 Vpk-pk at white
% Reflected = < 5%
% Visual power = 100%
% Aural power = 100%
% Exciter = The level on the meter
needed to attain 100% output power
from the transmitter
Refer to the test specifications sheet for
the transmitter for the actual reading:
•
•
ALC = .8 VDC
Audio = ±25 kHz with a balanced
audio input or ±75 kHz with a
composite audio input
Samples are provided for the remote
metering of the exciter at J1-10, the
visual at J8-26, the aural at J8-27, and
the reflected at J1-5.
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.
The +12 VDC is split when it is connected
to the board. Four of the +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 are fed to any
external amplifier trays for use in their
logic circuits. The resistors are for current
limiting and the diodes are to prevent
4-21
1000 Watt VHF High Band Transmitter
Chapter 4, Circuit Descriptions
voltage feedback from the external
amplifier trays.
offset null adjust R48, which are adjusted
to set up the visual power calibration.
4.1.9 (A19) Visual/Aural Metering
Board (1265-1309; Appendix D)
4.1.9.2 Visual Level Circuit
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.
The board also provides adjustments for
the calibration of the readings on the
meter. These readings are attained from
samples of the forward power and
reflected power outputs of the tray.
A forward power sample, visual + aural,
is applied to SMA jack J1 on the board.
The input signal is split, with one path
connected to 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,
the intercarrier filter, can be 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, that is a
good representation of the aural level.
The 4.5 MHz signal is fed to buffer
amplifier U6A. The output of U6A is
detected by diode detector CR3 and U1A
and then fed through 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 aural null adjust R51 and
430B, Rev. 0
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-with-sync output. The
visual-with-sync output is fed to a peakdetector circuit consisting of CR5 and
U2A. The signal is then fed through 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 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. Inputs to U2C also come from
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. 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 gate
amplitude adjust R25 and then applied to
the minus input of U1C. At this point, it is
inserted into the visual + aural signal
4-22
1000 Watt VHF High Band Transmitter
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-withsync output is fed to a peak-detector
circuit, consisting of CR5 and U2A, and
then fed through 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 diode detector CR7 and U3B.
The detected output is fed through
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 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. The +12 VDC also connects to
U5, a 5-VDC regulator that provides the
voltage needed to operate U4. The -12
VDC is applied to J5, pin 1, and is
isolated and filtered by L5 and C35
before it is connected to the rest of the
board.
4.1.10 (A4-A14) Channel Oscillator
Assembly, Dual Oven (1145-1202;
Appendix D)
The channel oscillator assembly contains
the channel oscillator board (1145-1201)
that generates a stable frequencyreference signal of approximately 100
430B, Rev. 0
Chapter 4, Circuit Descriptions
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 of 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.
4.1.11 (Optional) (A4-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.
4-23
1000 Watt VHF High Band Transmitter
The scans in U4 will continue until 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
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 J32.
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.
430B, Rev. 0
Chapter 4, Circuit Descriptions
4.1.12 (Optional) (A4-A12) IF
Attenuator Board (1150-1201;
Appendix D)
The (Optional) 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 amplitudemodulated aural IF signal at J2, the aural
IF output jack of the board.
4.2 (A6 and A7) VHF High Band
Amplifier Trays (1301169;
Appendix C)
The On Channel RF signal (+3 dBm pksync + aural), enters the rear of the
Tray at the "BNC" Jack J1 and is fed
through J1 of the (A1) Enclosure
Assembly to J1 of (A1-A1) the Phase
Shifter Board (1198-1603).
4.2.1 (A1-A1) Phase Shifter Board
(1198-1603; Appendix D)
The Board provides a Phase Shift
adjustment of the RF Signal that is
needed to provide maximum output
during the combining the two VHF
Amplifier Trays in the transmitter. A
front panel mounted Phase Shift
Potentiometer (R2), which connects to
J3 of the Board, 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
4-24
1000 Watt VHF High Band Transmitter
occurs, the AGC Control Board generates
a Fault Output at J1 that is connected to
J4 on the Filter/Amplifier Board. The
Fault cuts back the RF Signal level using
the Pin Diode Attenuator Circuit located
on the Filter/Amplifier Board.
The output at J2 of the Phase Shifter
Board is directed to J1 the input jack on
(A2) an enclosure that contains the
filter/amplifier board and the high band
driver pallet.
4.2.2 (A2-A1) Filter/Amplifier Board
(1301178; Appendix D)
The phase controlled output of the Phase
Shifter Board (+7 dBm pk-sync + aural)
is directed to the (J7), the Input Jack of
(A2-A1) a Filter/Amplifier Board
(1301178) which 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 is connected to the second circuit
that contains two amplifiers. The RF
connects through a Pin Diode Attenuator
Circuit to an amplifier IC U1. The
amplitude of the RF Signal through the
Pin Diode Attenuator Circuit is controlled
by the voltage applied to J4 the External
Control Jack of the Board. The Jumper
W1 on J5 should be between Pins 2 & 3
which provides for external control thru
J4 of the Gain of the Board and therefore
the Output level of the Tray. The front
panel mounted Gain Pot (R3) connects to
the AGC Control Board and adjusts 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 +12 dBm
pk-sync + aural that is connected to the
output of the board at J2.
430B, Rev. 0
Chapter 4, Circuit Descriptions
4.2.3 (A2-A2) High Band Driver
Pallet (P-10-VHF-H; Appendix D)
The RF output of the Filter/Amplifier
Board connects to J1 on (A2-A2) the High
Band VHF Driver Pallet (P10-VHF-H)
made by Delta RF Technology. The
board contains a RF Power FET that has a
gain of approximately 20 dB.
The RF output of the Board at J2 (+31
dBm pk-sync + aural) connects to J2 of
(A3) a RF enclosure, which contains the
Overdrive Protection Board, the High
Band Amplifier Board and the 3 Way
Splitter Board.
4.2.4 (A3-A1) Overdrive Protection
Board (1198-1601; Appendix D)
The signal is connected to J4 of (A3-A1)
the Overdrive Protection Board (11981601).
The RF Signal is thru 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 consisting of
CR1 and U1A. The gain of amplifier U1D
is controlled by the Detector Gain Pot
R11 which is set to +.4 VDC as measured
at TP1. The set output level of U1D is
connected to the comparator IC U1B.
The Trip Point for the comparator is
adjusted by R12, typically to 110%
Output Power. 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 light. Typically the output
power level, will bounce Down, then Up
in level and continue bouncing until the
Output Level is lowered to 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 and is a
Normal occurrence. The greater the
output level is above 110 %, the larger
the bounce.
4-25
1000 Watt VHF High Band Transmitter
Chapter 4, Circuit Descriptions
4.2.5 (A3-A2) High Band VHF
Amplifier Pallet (P200-VHF-H;
Appendix D)
RF Output at J5 of the Combiner which
connects to J2, the RF Output Jack of the
Tray.
The RF Output of the Overdrive
Protection Board at J5 connects to J1 on
(A3-A2) the High Band VHF Amplifier
Pallet (P200-VHF-H) made by Delta RF
Technology. The pallet amplifies the RF
to approximately +45 dBm pk-sync +
aural.
The 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. The Reflected Output Power
Sample connects to J5 on (A13) the AGC
Control Board.
The output of the high band VHF
amplifier pallet at J2 connects to J1 on
(A3-A3) the 3 Way Splitter Board
(1301161).
4.2.6 (A3-A3) 3 Way Splitter Board
(1301161; Appendix D)
The Splitter Board takes the +45 dBm
and provides three +40 dBm outputs that
connect to J1, J2 and J3 of (A4) the final
Amplifier Enclosure.
4.2.7 (A4-A1 thru A3) VHF Output
Amplifier Pallets (P400-VHF-H;
Appendix D)
The three RF outputs connect to (A4) the
Final Amplifier Enclosure, which contains
three (A4-A1, A4-A2 & A4-A3) High Band
Output Amplifier Pallets (P400-VHF-H)
made by Delta RF Technology. The RF
Signals connect to J1 on each of the High
Band Output Amplifier Pallets. Each
amplifier pallet provides approximately
13 dB gain.
The RF signal inputs to the Output
Amplifier Boards (+40 dBm) are
amplified to +53.3 dBm pk-sync + aural
outputs at J2 of each board. The outputs
are connected to J1, J2 and J3 on (A5A1) a 3 Way Combiner Board (1301157).
4.2.8 (A5-A1) 3 Way Combiner
Board (1301157; Appendix D)
The 3 Way Combiner takes the three
+53.3 dBm pk-sync + aural inputs and
combines them to form the approximate
600 Watt (+57.8 dBm pk-sync + aural)
430B, Rev. 0
4.2.9 (A13) AGC Control Board
(1142-1601; Appendix D)
The AGC Control Board contains two
peak detector networks which provide
detected outputs that are used for Front
Panel and Remote Meter Indic ations of
Forward and Reflected Output Power
Levels, AGC Detector Voltage Level and
also the VSWR Cutback protection if the
Reflected Power level increases above
the preset level.
The AGC Control Board provides AGC,
VSWR Cutback and Module Fault
operations for the VHF amplifier tray in
which it is mounted.
4.2.9.1 LED Status Indicators
A -12 VDC Enable from the Exciter tray is
applied to J10 Pin 10. This Negative
Enable causes the J-FET Q9 to be Biased
OFF and a High to be applied to Q4 that
is Biased On that lights the front panel
Enable Indicator. The High is also
applied to J10 Pin 6 that is a High Enable
to the Switching Power Supply, only if
there is no Overtemperature Fault, which
is a Low applied to J10 Pin 5. The High
also connects to the Base of Q8 that
forward Biases it and connects a Low to
Q7 which Biases it Off. If the Output
Power Level of the Tray is above the
preset level and Q7 is biased Off, Q6 and
Q5 will be Biased On and the Module
Status Indicator LED will be illuminated.
If the Enable is removed from J10 Pin 10,
Q9 will turn On applying a Low to Q4 and
4-26
1000 Watt VHF High Band Transmitter
to Q8. The Low to Q4 turns it Off which
extinguishes the Enable Indicator at J108. The Low to Q8 turns it Off which turns
On Q7 causing a Low to be applied to Q5
and Q6 that are Biased Off which turns
Off the Module Status Indicator.
A voltage sample from the Switching
Power Supply is applied to Jack J9 Pin 1
of the Board and is connected through
R86 to the front panel Meter for
monitoring. R86 is adjustable to
calibrate the voltage reading on the front
panel meter.
4.2.9.2 Front Panel Metering
A Forward Power Sample of the output of
the Tray is applied to Jack J4 of the
Board. CR11 along with C16 and L3
detect the Peak Level that is then
buffered by U3C, amplified by U3D and
applied to the Front Panel Meter. R44 is
adjustable to calibrate the % Forward
Power indication on the Front Panel
Meter. A Forward Power Sample also is
sent to the Remote Interface Panel. The
Input Forward Power Sample at J4 is split
and fed to the divider R40 and R39 and
then to the Front Panel through Jack J3
for monitoring.
A Sample of the Reflected Power output
of the Tray is applied to Jack J5 and is
detected in the same manner as the
Forward Power. R53 calibrates the Front
Panel Meter in the % Reflected Power
position.
4.2.9.3 Automatic Gain Control
The board contains the Automatic Gain
Control (AGC) function for the Tray in
which it is mounted. An AGC Reference
level input from the Upconverter Tray is
applied to J6 Pin 2 and is amplified by
U3B. The Output of U3B is split with one
path directed to the Front Panel Gain
potentiometer that sets the Output Power
Level of the Tray. The Voltage at the
arm of the Front Panel Gain Pot is
amplified by U2C and compared to the
Output Power of the Tray by U2D. The
430B, Rev. 0
Chapter 4, Circuit Descriptions
Error Voltage from U2D is sent through
J1, when S1 is in the Auto position, to
the Variable Gain/Phase Board on which
it connects to the Pin Diode Attenuator
circuit. This AGC Voltage Level is
metered on the front panel through J13.
The Tray can also be operated in Manual
Gain by switching S1 to the Manual
Position and adjusting R5 for the desired
Output Power Level.
The other path at the output of U3B,
directs the Input AGC Voltage to the
amplifier U6D whose output is fed to the
(+) Input of the comparator U6C. A
Sample of the Forward Power Level of
the Tray at U3D is amplified by U6A and
fed to the (-) Input of the comparator
U6C. The two levels are compared by
U6C and the result is fed to U6B whose
output is controlled by the reference level
set by R75 and R76. If the Difference
between the Output Power Level and the
Input Level drops significantly, U6B Pin 7
goes Low, Q5 and Q6 Turn Off causing
the Module Status LED to go out and the
Remote Module Status to be removed.
4.2.9.4 Operational Voltages
U7 is a 3 Terminal Regulator IC that
takes the +28 VDC input from the
Switching Power Supply and produces
the +12 VDC needed for the operation of
the Board. U8 is a +5 VDC Regulator
that takes the +12 VDC input from the
Exciter Tray or from the Board and
produces the +5 VDC needed to power
the front panel Indicators. Using the +12
VDC from the Exciter Tray permits the
operation of the Front Panel Indicators
even if the Switching Power Supply is not
Turned On.
4.2.10 (A10) +28 VDC Switching
Power Supply Assembly
(A10) The +28 VDC Switching Power
Supply uses the AC input through the
15A circuit breaker CB1 and provides the
+28 VDC needed for operation of the
tray.
4-27
1000 Watt VHF High Band Transmitter
The +28 VDC output of the switching
power supply assembly connects to (A8)
the Current Metering Board.
4.2.11 (A8) Current Metering Board
(1301316; Appendix D)
The Current Metering Board distributes
the voltages through fuses to the
Amplifier Devices on the Filter/Amplifier,
High Band Driver Board, the High Band
Amplifier Board and the three Final High
Band Amplifier Boards. The Fuses F1, F2
& F3 are 15 Amp, F4 is 5 Amp, F6 is 2
Amp and F7 is 1 Amp Fuse. F5 is not
used in this configuration. There are two
Spare Fuses, one 1 Amp and one 15
Amp, located on the top, right rear of the
Tray.
Fuse F1 protects (A4-A1) the High Band
Output Amplifier Pallet, Fuse F2 protects
(A4-A2) the High Band Output Amplifier
Pallet, Fuse F3 protects (A4-A3) the High
Band Output Amplifier Pallet, Fuse F4
protects (A3-A2) the High Band Amplifier
Pallet, and Fuse F6 protects (A2-A1) the
Filter/Amplifier Board. Fuse F7 supplies
+28 VDC to J8 Pin 2 on the AGC Control
Board. The +28 VDC is connected to the
Regulator IC U7 that takes the +28 VDC
and provides a +12 VDC output.
The +12 VDC is used for operation of the
AGC Control Board and also the +12 VDC
is connected through the Current
Metering Board, jumper from TB1-5 to
TB1-6, to the Phase Shifter Board, the
Filter/Amplifier Board and the 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) P400 High Band
Output Amplifier Board, (I2 ) for the (A4A2) P400 High Band Output Amplifier
Board and (I3 ) for the (A4-A3) P400 High
Band Output Amplifier Board. The (ID )
position reads the current for the (A3-A2)
P200 High Band Amplifier Board. To read
430B, Rev. 0
Chapter 4, Circuit Descriptions
the desired current, Switch S2 to the
proper position checking that S1 is in the
Current position. These current readings
can be used when setting up the Idling
Currents, no RF Drive applied, for the
devices. (I1 , I2 & I3 ) are set for 6 Amps
max. ID is set for 3 Amps max. (NOTE:
All front panel current readings must be
multiplied by 2 for the proper readings.)
4.2.12 Operation of the VHF
Amplifier Tray
The 220 VAC from the AC distribution
panel is applied through Jack J4 to
Terminal Block TB1 in the Tray. When
(CB1) the 15 Amp rear panel mounted
AC Circuit Breaker is switched On, the
220 VAC is distributed from TB1 to (A11
& A12) two cooling Fans, which will
operate, and to (A10) the Switching
Power Supply. There are two Surge
Suppressors, VR1 and VR2, mounted on
TB1 that provide protection from
transients or surges on the input AC Line.
There are two Surge Suppressors, VR3
and VR4, mounted at the input to the
switching power supply from each AC
Line to ground, which also provide
protection from transients or surges on
the AC Line.
The switching power Supply only
operates when the Power Supply Enable
Control Line, Jack (J3 Pins 9 & 10),
located on the rear of the Tray, are
shorted. The Enable is generated by the
VHF exciter tray when the transmitter is
switched to Operate. The Enable is
applied to (A13) the AGC Control Board
(1142-1601), which, if there is no
Thermal Fault, connects the Enable from
J10 Pins 6 & 7 to J2-6 & 4 on the
Switching Power Supply Assembly. The
Green Enable Front Panel LED (DS2) will
light, indicating an Enable is present. If
the Amplifier Array is in Standby or if a
Thermal Fault occurs, the AGC Control
Board will not Enable the Switching
Power Supply, therefore the +28 VDC will
be removed from the Amplifier Modules
and the Front Panel Enable LED and
Module Status LEDs will be out.
4-28
1000 Watt VHF High Band Transmitter
The front panel Meter (A9), using (S1)
the Front Panel Selector Switch, monitors
the AGC Voltage, % Output Reflected
Power, % Forward Power and the
Switching Power Supply Voltage (+28
VDC). The Meter in the AGC position will
read anywhere from 1 Volts to 2 Volts.
The Meter is calibrated in the Power
Supply position using R86 located on the
AGC Control Board. The % Output Power
is calibrated using R44 and the %
Reflected Power is calibrated using R53,
located on the AGC Control Board. With
S1 in the Current Position, S2 is switched
to read the Idling Currents, no RF Drive
applied, of the High Band Output
Amplifier Boards.
Typical operating readings are an RF
Current of 12 Amps for the three final
P400 Amplifier Pallets I1 , I2 & I3 positions
and 6 Amps for the P200 High Band
Amplifier pallet in the ID position. These
readings are with 100 % output power
for the transmitter with a black picture.
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 thru
the detector circuit to a VSWR Cutback
circuit (U13C). If the Reflected power
increases above 20 %, the output power
of the Tray, as set by R60 (VSWR
430B, Rev. 0
Chapter 4, Circuit Descriptions
Cutback) on the AGC Control Board, will
be cutback to maintain a 20 % Reflected
Output level. The Red LED (DS4) VSWR
Cutback, located on the front panel, will
remain lit until the Reflected level drops
below 20 %.
There are three Thermal Switches in the
amplifier Tray for overtemperature
protection. Two of the Thermal
Switches (A4-A5 & A4-A6) are mounted
on the rear of (A4) the heatsink for the
High Band Amplifier Pallets and the third
Thermal Switch (A5-A2) is mounted on
the heatsink for (A5-A1) the 3 Way
Combiner Board. The Thermal Switches
close when the heatsink on which it is
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, eliminating the +28 VDC,
and also to light the Red LED Indicator,
Overtemperature (DS5), mounted on
the front panel. The AGC Control Board
extinguishes the Module Status LED
(DS3).
This completes the circuit descriptions for
the VHF amplifier tray, and also for the
other trays, assemblies, subassemblies
and boards that make up the 430B
Transmitter.
4-29
1000 Watt VHF High Band Transmitter
Chapter 5, Detailed Alignment Procedures
Chapter 5
Detailed Alignment Procedures
The 430B transmitter was aligned at the
factory and should not require additional
alignments to achieve normal operation.
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 TB11 (+), 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 exciter panel are loop-through
connected and the unused jack can be
used as an audio source for another
transmitter by removing jumper W1 on
jack J15 on the aural IF synthesizer.
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 (A9)
the bandpass filter assembly is
terminated into a dummy load of at least
1000 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.
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 video
level control R12 on the sync tip clamp/
modulator board.
Switch on the main AC and the VHF
exciter circuit breakers on the AC
distribution panel behind the rear cabinet
door.
Switch the meter to the Audio position to
show 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
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.
5.1 (A4) VHF High Band Exciter Tray
(1070901; Appendix C)
5.1.1 VHF High Band Exciter Tray
with Baseband Video and Audio
Inputs
The (A4) VHF high band exciter tray
(1070901) 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 can be
used as a video source for another
transmitter by removing jumper W4 on
430B, Rev. 0
5.1.2 VHF H.B. Exciter Tray with the
(Optional) 4.5-MHz Composite Input
Kit
With the 4.5-MHz composite input kit,
the (A4) VHF exciter tray (1070901) is
5-1
1000 Watt VHF High Band Transmitter
Chapter 5, Detailed Alignment Procedures
able to operate using either the separate
video and audio baseband inputs or the
single 4.5-MHz composite input. The 4.5MHz composite input kit includes a
composite 4.5-MHz filter board (12271244) and a 4.5-MHz bandpass filter
board (1265-1307).
The IF section of the VHF H.B. 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.
To align the VHF exciter using baseband
video and audio, refer to the alignment
instructions for baseband inputs
described in this chapter. Select the
baseband input operation by applying a
baseband select, using a jumper or
closed contacts, connected between J7-6
and J7-7 on the rear of the tray.
Move the Operate/Standby switch on the
VHF exciter tray to Operate. The setup
of the RF output includes an adjustment
to the drive level of the two 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 two VHF
amplifier trays.
To operate the transmitter using the 4.5MHz 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
video input jack J2 on the A/V input &
remote interface panel. On (A24) the
composite 4.5-MHz filter board (12271244), 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.
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:
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.
5.1.3 VHF H.B. Exciter Tray with
either Baseband or the 4.5-MHz
Composite Input
430B, Rev. 0
5-2
•
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
•
DS4 (Mute) – Indicates that a visual
Mute command is present (not used
in this configuration)
•
DS5 (Modulator Enable) – Indicates
that the modulator IF output has
been selected (this is only used if a
1000 Watt VHF High Band Transmitter
Chapter 5, Detailed Alignment Procedures
receiver tray is present in the
system). DS5 is always on with no
receiver.
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 J7-6
and J7-7 on the rear of the tray.
The ALC is muted when the transmitter is
in Standby. To monitor the ALC, turn off
the two amplifier on/off circuit breakers
on the AC distribution assembly at the
rear of the cabinet and 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
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 two VHF
amplifier trays where it is used as a
reference for the automatic gain control
(AGC) in each amplifier 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 (J2) and
the baseband audio to the proper
baseband audio input on the A/V input &
remote interface panel. For balanced
audio input, connect TB1-1(+), TB12(grnd), and TB1-3 (-). For
composite/stereo audio, connect the
composite audio input jack (J6). Connect
a baseband select from J7-6 and J7-7 on
the rear of the exciter tray.
5.1.4 VHF H.B. Exciter Tray Board
level Adjustments
5.1.4.1.1 (Optional) (A24) Composite
4.5-MHz Filter Board (1227-1244;
Appendix D)
5.1.4.1 (Optional) 4.5-MHz
Composite Input Kit
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:
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 (12271244; Appendix D) and the (A25) 4.5MHz 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
430B, Rev. 0
5-3
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.
1000 Watt VHF High Band Transmitter
Chapter 5, Detailed Alignment Procedures
The output at J6 and J7 on the board
should be video only, without the 4.5MHz aural subcarrier.
3.
5.1.4.1.2 (Optional) (A25) 4.5 MHz
Bandpass Filter Board (1265-1307;
Appendix D)
Tune the four stages of the board
using the variable inductors (L1-L4)
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.
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:
5.1.4.3 (A7) IF Carrier Oven
Oscillator Board (1191-1404;
Appendix D)
1.
To align this board:
2.
2.
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.
Adjust C19 for an overall peak-topeak variation of less than ±0.3 dB
from 4.4 MHz to 4.6 MHz.
Recheck the frequency response; it
may have changed with the
adjustment of the envelope delay.
If necessary, retune the board.
5.1.4.2 (A6) Delay Equalizer Board
(1227-1204; Appendix D)
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.
5.1.4.4 (A5) Sync Tip
Clamp/Modulator Board (12651302; 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.
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
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.
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.
430B, Rev. 0
5-4
1000 Watt VHF High Band Transmitter
4.
Chapter 5, Detailed Alignment Procedures
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.
Set the controls of the
demodulator to the following:
Move jumper W7 on J4 to the
Clamp Disable position. Readjust
pot R41, manual offset, for the
correct depth of modulation by
observing the demo dulated
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.
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
The following test setup is for the
adjustment of the depth of
modulation and ICPM at IF:
Remove the cable that is on
J18 and connect the doublesideband, 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.
430B, Rev. 0
C.
8.
Figure 5-1. Waveform
A.
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).
Detector mode – Cont
Sound trap – In
Zero carrier – On
Auto – Sync
Audio source – Split
De-emphasis – In
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.
7.
B.
5-5
1000 Watt VHF High Band Transmitter
Chapter 5, Detailed Alignment Procedures
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.
16.
17.
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
5.1.4.5 (A4) Aural IF Synthesizer
Board, 4.5 MHz (1265-1303;
Appendix D)
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.
1.
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-ofband products. Adjust pot R97 for
-20 dBm at J16.
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).
2.
18.
While still monitoring J20 with a
spectrum analyzer, readjust R62,
visual IF gain, for a 0 dBm visual
430B, Rev. 0
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.
5-6
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 TB13 (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.
D.
Connect a cable from the 600Ω
audio output jack of the
demodulator to the input of an
audio distortion analyzer.
Set the output frequency of the
audio oscillator to 400 Hz and the
output level to +10 dBm.
1000 Watt VHF High Band Transmitter
Chapter 5, Detailed Alignment Procedures
3.
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%)
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
4.
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.
5.1.4.6 (A8) ALC Board (1265-1305;
Appendix D) (Part 1 of 2)
Adjust R13, balanced audio gain, on
the aural IF synthesizer board for
±25-kHz deviation.
Table 5-2 describes the functions of each
LED on the ALC board (A8).
Table 5-2. ALC Board LEDs
LED
DS1 (Red LED)
DS2 (Red LED)
DS3 (Red LED)
DS4 (Red LED)
DS5 (Green LED)
1.
FUNCTION
Indicates that an abnormally low IF signal level is
present at IF input connector J1
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
Indicates a video loss fault
Indicates that a Mute command is present
Indicates that the output from the modulator is
selected as the input to the board
To align the ALC board, preset the
following controls on the tray:
B. IF Phase Corrector Board (12271250)
A. ALC Board (1265-1305)
Move W2 on J9 to phase
correction: enable. Move W3 on
J10 to amplitude correction:
disable.
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).
2.
Adjust R87, manual gain pot, to
mid-range.
430B, Rev. 0
5-7
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
1000 Watt VHF High Band Transmitter
Chapter 5, Detailed Alignment Procedures
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 flatfrequency 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.
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 midrange 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 mo nitor 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.
5.1.4.7 (A9) IF Phase Corrector
Board (1227-1250; Appendix D)
The signal level into the board should be
approximately the same as the output of
the board.
The IF input jack 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 is fed to the J7 IF I/P
jack of the ALC board (A8).
5.1.4.8 (A8) ALC Board, NTSC (12651305; Appendix D) (Part 2 of 2)
To align this board:
NOTE: The following step affects the
response of the entire transmitter.
1.
Input a multiburst video test signal.
Connect a spectrum analyzer to
J11. Tune C63 for a flat-frequency
response of ±0.5 dB.
8.
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.
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
of the transmitter. R103 and R106
are used to adjust the depth and
width of the correction notch.
4.
Place jumper W3 on J6 in the Auto
mode and adjust the front panel
power adjust control A20 fully CW.
9.
Refer to Section 5.5 of this chapter
for the system alignment
procedures for the linearity
430B, Rev. 0
5-8
1000 Watt VHF High Band Transmitter
Chapter 5, Detailed Alignment Procedures
correctors. Controls R13, R18, and
R23, the magnitude controls,
should be set fully CW. Controls
R34, R37, and R40 are the linearity
cut-in adjustments.
3.
5.1.4.10 (A11-A1) x4 Multiplier
Board (1174-1112; Appendix D)
5.1.4.9 (A14-A1) Channel Oscillator
Board, Dual Oven (1145-1201;
Appendix D)
While monitoring the board with a DC
voltmeter, maximize each test point
voltage by tuning the broadband
multipliers in the following sequence:
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.
3.
Reconnect the main output (J1) of
the channel oscillator to the input
(J1) of the x4 multiplier.
1.
Monitor TP1 with a DVM and tune
C4 for maximum voltage. Monitor
TP2 with a DVM and tune C6 and
C10 for maximum voltage.
Monitor TP3 with a DVM and tune
C12; repeak C4, C6, and C10 for
maximum voltage.
2.
Connect a spectrum analyzer,
tuned to four times the crystal
frequency, to the x4 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.
Connect a spectrum analyzer to J6 on
board. Adjust C23 and C26 to determine
the center frequency. Use C2 and C7 to
locate the upper and lower channel-edge
shaping. C24 is used to determine the
channel bandwidth.
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.
The output of the x4 multiplier connects
to (A11-A1) the filter/mixer board.
NOTE: Do not repeak C6, C18, L2, or
L4. This may change the output
level.
5.1.4.11 (A11-A2) VHF Filter/Mixer
Board (1150-1102; Appendix D)
To align the board:
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.
430B, Rev. 0
1.
5-9
Monitor J4, the LO output of the
board, with a spectrum analyzer
and adjust C12 and C18 for
maximum output at the LO
frequency and minimum out-ofband products. Adjust C13 and
C17 for the best frequency
response for the LO frequency.
1000 Watt VHF High Band Transmitter
Chapter 5, Detailed Alignment Procedures
2.
The idling current for the amplifier boards
are adjusted with no RF drive applied. S1
should be in the Auto AGC position for
the normal operation of the transmitter.
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.
5.1.4.12 (A11-A3) High-Band VHF
Filter/Amplifier Board (1064252;
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 filtered output connects to J1 of the
board and is amplified by U1 to a
nominal +12 dBm visual and +2 dBm
aural level by adjusting R9. The output at
J2 is fed to J4 on the A11 enclosure and
from there to J15 on the rear of the tray.
To align the board, use a multiburst or
sweep video signal inserted into the
exciter tray.
Reconnect the cable 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 manual
gain adjust R9 for a +12 dBm peak
visual output.
The VHF exciter tray is aligned and ready
for normal operation.
5.2 (A6 and A7) VHF High Band
Amplifier Tray (1301169; Appendix C)
The (A6 and A7) VHF high-band amplifier
tray has 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 tray should not need to
be adjusted to attain normal operation.
Any adjustments to the boards in this
tray should be performed in the Manual
Gain position, with S1 on (A13) the AGC
control board (1142-1601) in Manual.
430B, Rev. 0
Connect a dummy load with a rating of a
least 600 watts to J2, the RF output jack
of the tray.
5.2.1 (A13) AGC Control Board
(1142-1601; Appendix D)
Using a calibrated wattmeter, check that
the tray is operating at the rated power.
Remove cable connected to the forward
power sample input jack J4 on the (A13)
AGC control board (1142-1601). The
output power level should drop to 20%
because of the VSWR cutback setting and
the VSWR LED DS4 should be
illuminated. The front panel Module
Status LED should not be lit.
Reconnect J4 on A13 and adjust R59 on
the AGC control board to begin cutting
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
+28 VDC by adjusting pot R86 on the
AGC control board.
5.2.2 (A1-A1) Phase Shifter Board
(1198-1602; Appendix D)
There are no adjustments to (A1-A1) the
phase shifter board (1198-1602). The
front panel has adjustments for phase
that are made during the amplifier array
setup procedure.
5.2.3 (A2-A1) VHF Filter/Amplifier
Board (1301178; Appendix D)
The (A2-A1) VHF filter/amplifier board
has approximately 5 dB of gain. Tune
the channel filter capacitors C20 and C29
(loading), C23 and C26 (center
frequency), and C24 (coupling) at J6 on
the board for the best response.
5-10
1000 Watt VHF High Band Transmitter
Chapter 5, Detailed Alignment Procedures
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 R20 (two 1Ω
resistors in parallel on the filter/amplifier
board) and adjust R13 for .125 volts
(using Ohms’ Law: [E=I x R] : [E=250
mA x .5 Ω] : E=125 mV).
This
board
contains
no
tuning
adjustments. The board takes the +45
dBm input and splits it into three equal
+40 dBm outputs.
5.2.4 (A2-A2) VHF High Band
Amplifier Board (P10-VHF-H;
Appendix D)
These boards 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 13 dB of gain
and the output is typically +53.3 dBm.
This board is supplied by Delta RF
Technology, Inc. Refer to the data
sheets in the subassembly section of this
manual for more information. The board
has approximately 19 dB of gain and the
output is typically +31 dBm.
5.2.5 (A3-A1) Overdrive Protection
Board (1198-1601; Appendix D)
The level of the RF input and output of
the (A3-A1) overdrive protection board
(1198-1601) should be +31 dBm during
normal operation.
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
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%.
5.2.6 (A3-A2) VHF High Band
Amplifier Board (P200-VHF-H;
Appendix D)
5.2.8 (A4-A1 thru A3) VHF Output
Amplifier Pallets (P400-VHF-H;
Appendix D)
5.2.9 (A5-A1) 3 Way Combiner
Assembly (1301157; Appendix D)
There are no adjustments to the (A5-A1)
3 way combiner assembly. The three
+53.3 dBm inputs are combined to
produce the 600 watts peak of sync +
aural output (+57.8 dBm) at the RF
output jack J5 of the combiner.
J5 of the combiner connects to J2 the RF
Output Jack of the VHF Amplifier Tray.
5.2.10 Calibration of the Visual Plus
Aural Output Power and VSWR
Cutback of the VHF amplifier tray
Check that a dummy load of at least 600
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:
This board is supplied by Delta RF
Technology, Inc. Refer to the data
sheets in the subassembly section of this
manual for more information. The board
has approximately 14 dB of gain and the
output is typically +45 dBm.
1. Remove the J16 cable from (A5) the
sync tip clamp/modulator board
(1265-1302) in the exciter tray. Set
Manual AGC switch S1, on the (A13)
AGC control board (1142-1601) in the
VHF amplifier tray, to the Manual
position.
5.2.7 (A3-A3) 3 Way Splitter Board
(1301161; Appendix D)
2. Connect a sync and black test signal
to the video input jack of the remote
430B, Rev. 0
5-11
1000 Watt VHF High Band Transmitter
Chapter 5, Detailed Alignment Procedures
interface panel. Switch the
transmitter to the Operate position.
+ aural output. 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.
3. Adjust the manual gain pot R5 on the
AGC control board for:
•
•
Sync + black 0 IRE setup;
wattmeter=360 watts
Sync + black 7.5 IRE setup;
wattmeter=325 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 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.
5. 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%.
6. Switch Off the tray and reverse the J6
and J7 cables on the 3 way combiner
board. 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 panel lights.
This sets up the VSWR cutback
circuitry.
7. Readjust R5 for 100% on the meter
to achieve a 600 watts peak of sync
430B, Rev. 0
Switch Off the tray and return the J6 and
J7 cables on the 3 way combiner board
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.
There is a spare 1 amp and 10 amp fuse
on the top, right-hand side of the tray.
These are replacements for fuses on the
current metering board.
The VHF high band amplifier tray is
aligned, calibrated, and ready for normal
operation. Repeat as needed for the
other amplifier tray.
5.3 Phase and Gain Adjustment of
the 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.
Preset the phase and gain potentiometer
on each VHF amplifier tray fully CCW.
Switch the transmitter to Operate and
adjust the gain pot on each tray for 25%
Output Power. Adjust the phase control
CW on the left VHF amplifier tray. If the
% Visual Output Power goes up, continue
to adjust the phase control until either
the peak is reached or the end-of-travel
is reached. If the % Output Power goes
down, reset the phase control on the VHF
amplifier tray fully CCW and repeat the
above procedure with the phase control
of the other amplifier tray.
5-12
1000 Watt VHF High Band Transmitter
If the end-of-travel is reached on the
phase adjust, reset the phase control
CCW and add a 2-inch length of cable to
the input of the affected VHF amplifier
tray at J1. Readjust the phase of that
tray until a peak is reached or until the
end-of-travel is achieved. If the end-oftravel is reached, repeat the above
procedure and replace the 2-inch length
of cable with a 4-inch length of cable.
Once a peak has been reached, move the
phase control that is fully CCW up two
turns and repeak using the phase control
on the other tray. This allows both trays
to have some range of adjustment.
Adjust the gain of both VHF amplifier
trays for 90% Tray Output Power.
Readjust each phase control to peak the
combined output; the phase should only
have been slightly affected. Although it
may take a few turns to notice a change,
there should be a definite peak that is
achieved while adjusting the phase of
each tray. Raise or lower the output
power of each tray to achieve 100%
Output Power. The output power of each
tray should be 90% to 100%.
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
approxima tely compensate the
corresponding non-linear distortions of
the 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 counterclockwise (CCW). R68 is the range
adjustment and should be set in the
middle of the range. The phase
correction Enable/Disable jumper W2 on
430B, Rev. 0
Chapter 5, Detailed Alignment Procedures
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. While
changing the input signals, switch the
transmitter to Standby. 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.
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, 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 threshold
point. Refer to the VHF exciter tray
5-13
1000 Watt VHF High Band Transmitter
Chapter 5, Detailed Alignment Procedures
control locations drawing, ALC board
(1265-1305), 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.
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.
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
of the ALC board is enabled 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. While
changing the input signals, switch the
transmitter to Standby. 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 IF ALC
board (1265-1306), preset pots R34,
R37, and R40 (threshold) 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 IF 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.
430B, Rev. 0
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 Calibration of the Forward
Output Power Level of the
Transmitter
NOTE: Only perform the following
procedure if the power calibration is
suspect.
Preset R51, the aural null pot, located on
the visual/aural metering board (12651309) in the VHF exciter, 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)
5-14
1000 Watt VHF High Band Transmitter
Chapter 5, Detailed Alignment Procedures
located in the VHF exciter. Connect a
sync and black test signal to the video
input jack of the VHF exciter tray. Switch
the transmitter to Operate.
and J4, and adjust R39 on the (A19)
visual/aural metering board (12651309), in the VHF exciter, for a 20%
reading in the Reflected Power position.
At this 20% 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 (A17)
transmitter control board (1265-1311) 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.
Set up the transmitter for the appropriate
average output power level: sync + black
0 IRE setup/wattmeter=595 watts; sync
+ black 7.5 IRE setup/wattmeter=545
watts.
Note: The transmitter must have 40 IRE
units of sync.
Adjust R28, visual calibration, on (A19)
the visual/aural metering board (12651309) 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.
5.7 Calibration of the Reflected
Output Level of the Transmitter
On the meter, in the Visual Power
position, turn the power adjust pot to
20%. Check that the jumper is in Manual
on (A11-A3) the VHF filter/amplifier
board (1064252), located in the VHF
exciter. Reverse the cables on A9, J3
430B, Rev. 0
Switch the transmitter to Standby. Move
the cables on A9, J3 and J4, to their
original positions. Switch the transmitter
to Operate and adjust the front panel
power pot for a 100% Visual Power
reading.
5.8 (A8) 2-Way Combiner Assembly
(1219-1006; Appendix C)
There are no adjustments to (A8) the
VHF combiner assembly (1219-1006).
5.9 (A9) Bandpass Filter Assembly
NOTE: The bandpass filter is a pre-tuned
vendor item and should not be tuned
without the proper equipment. If tuning
is required, consult the Axcera Field
Support Department before attempting
to make any adjustments.
This completes the alignment procedure
for the 430B Transmitter. If a problem
occurred during alignment, please
contact Axcera field service department
at 724-873-8100.
5-15
APPENDIX A
SYSTEM SPECIFICATIONS
VHF Solid State Transmitter/Translator
430B/432B - 1000 Watt High Band Transmitter/Translator
Visual Performance
Aural Performance
General
Power Output
1000W
Power Output (Average)
100W
Output Impedance
50 Ω
Distortion
0.5%
Frequency Range
174 to 216 MHz
FM Noise
-60 dB
Carrier Stability
±250 Hz
AM Noise
-55 dB
Altitude*
8,500 feet
Aural to Visual Separation
4.5 MHz,
±100 Hz
Transmitter Dimensions
Size (H x W x D)
Weight
69”x22”x34”
400 lbs
(Transmitters or Translators with FCR)
Frequency Translation Stability
±1 kHz
(Translators)
Regulation of RF Output Power
3%
Output Variation (Over 1 Frame)
2%
Sideband Response
-1.25 MHz and below
-0.75 to -0.5 MHz
-0.5 to +3.58 MHz
3.58 MHz to 4.18 MHz
-20 dB
-+0.5, -2.0 db
±0.5 dB
=0.5, -1.0 dB
Freq Response vs. Brightness
±0.5 dB
Differential Gain
5%
Incidental Phase Modulation
±3°
Linearity (Low Frequency)
5%
Differential Phase
±3°
Signal-to-Noise Ratio
55 dB
2t K-Factor
2%
Envelope Delay
Transmitters
Translators
Input Impedance
Freq Range (±0.5 dB resp.)
Per FCC
Standard
±40 ns
Video Input (Transmitters)
75 Ω
Harmonic Radiation
-60 dB
Intermodulation Products
-52 (red field)
Spurious
-60 dBm
-30°C to
+50°C
Operational Humidity Range
0% to 95%
(Non-condensing)
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
Operational Temperature Range
1V peak,
nominal
75 ohms,
unbalanced
20 kHz to
120 kHz
Line Voltage
230 V ±10%,
1 phase 50/60Hz
Power Consumption
3000 W (50% APL)
Options
Automatic Station Identifier
Spare Parts Kit
Modulator Option (Translators)
Remote Preamplifier(Translators)
UHF Frequency Correcting Receiver
(FCR Option Translators)
(>3 MHz from channel edge)
Noise Figure (Translator)
With Input Preamp
4.5 dB (max)
Input Dynamic Range
-65 to -25 dBm
(Translators)
Specifications 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 specifications
without prior notice. At any time, you may verify product specifications by contacting our office. 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.
0402R0
© 2004 Axcera
All Rights Reserved
103 Freedom Drive, PO Box 525, Lawrence, PA 15055
An Equal Opportunity Employer
t: 724-873-8100
f:724-873-8105
A Platinum Equity Company
www.axcera.com
430B/432B
APPENDIX B
SAMPLE LOG REPORT SHEET
& TYPICAL OPERATIONAL READINGS
1000 Watt VHF High Band Transmitter
Appendix B, Sample Log Report Sheet
(A4) VHF Exciter
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 High Band Amplifier Trays
(A6)
(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
AGC Sample = ____________V
AGC Sample = ____________V
Current I1 = ___________A
Current I1 = ___________A
Current I2 = ___________A
Current I2 = ___________A
Current I3 = ___________A
Current I3 = ___________A
Current ID = ___________A
Current ID = ___________A
Date __________________
Customer Name ______________________________ Call Letters ________________
Technician ___________________________________________
430B, Rev. 0
B-1
1000W VHF High Band Transmitter
Typical Readings
(A4) VHF Exciter
ALC = .8 VDC
% Exciter = The level needed to attain
100% output power from the
transmitter (Typically
between 80 & 90%)
% Reflected = < 10 %
% Visual Power = 100 % (1000 Watts
Peak of Sync)
% Aural Power = 100 % (100 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 High Band Amplifier Trays
(A6)
(A7)
AGC Voltage (0 to 10 V) = 1-2V
AGC Voltage (0 to 10 V) = 1-2V
% Reflected Power (0 to 120) = <10%
% Reflected Power (0 to 120) = <10%
% Output Power (0 to 120) = 90%
% Output Power (0 to 120) = 90%
Power Supply Voltage (0 to 100 V) = +28V
Power Supply Voltage (0 to 100 V) = +28V
Current I1 = 10 Amps
Current I1 = 10 Amps
Current I2 = 10 Amps
Current I2 = 10 Amps
Current I3 = 10 Amps
Current I3 = 10 Amps
Current ID = 5 Amps
Current ID = 5 Amps
430B, Rev. 0
B-2
APPENDIX C
SYSTEM DRAWINGS
1000 Watt VHF High Band Transmitter
Appendix C, System Drawings
430B System:
1000 Watt VHF Transmitter Block Diagram ..........................................1303856
1000 Watt VHF Transmitter Interconnect ...........................................1303857
1000 Watt VHF Transmitter Racking Plan ............................................1303855
AC Distribution Assembly
Interconnect..............................................................................1265-8600
VHF High Band Exciter Tray, M/N, Sync Tip Clamp
Block Diagram................................................................................1070906
Interconnect.................................................................................1070908
VHF High Band Amplifier Tray
Block Diagram................................................................................1301111
Interconnect.................................................................................1301078
430B, Rev. 0
C-1
APPENDIX D
SUBASSEMBLY DRAWINGS
1000 Watt VHF High Band Transmitter
Appendix D, Subassembly Drawings
AGC Control Board
Schematic ..................................................................................1142-3601
Channel Oscillator Board, Dual Oven
Schematic ..................................................................................1145-3201
VHF Filter/Mixer Board
Schematic ..................................................................................1150-3102
(Optional) IF Attenuator Board (Part of AM Identifier Kit)
Schematic ..................................................................................1150-3201
x4 Multiplier Board
Schematic ..................................................................................1174-3112
IF Carrier Oven Oscillator Board, 45.75 MHz
Schematic ..................................................................................1191-3404
Overdrive Protection Board
Schematic ..................................................................................1198-3601
Phase Shifter Board, VHF High Band
Schematic ..................................................................................1198-3603
Delay Equalizer Board
Schematic ..................................................................................1227-3204
(Optional) Composite 4.5-MHz Filter Board (Part of 4.5MHz Input Kit)
Schematic ..................................................................................1227-3244
IF Phase Corrector Board
Schematic ..................................................................................1227-3250
Sync Tip Clamp/Modulator Board
Schematic ..................................................................................1265-3302
Aural IF Synthesizer Board, 4.5 MHz
Schematic ..................................................................................1265-3303
ALC Board
Schematic ..................................................................................1265-3305
(Optional) 4.5-MHz Bandpass Filter Board (Part of 4.5MHz Input Kit)
Schematic ..................................................................................1265-3307
(Optional) EEPROM FSK Identifier Board (Part of 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
430B, Rev. 0
D-1
1000 Watt VHF High Band Transmitter
Appendix D, Subassembly Drawings
VHF High-Band Filter/Amplifier Board
Schematic .....................................................................................1064147
VHF Mixer/Amplifier Enclosure Assembly
Interconnect..................................................................................1088069
VHF Filter/Amplifier Board
Schematic .....................................................................................1301179
Current Metering Board, VHF High Band
Schematic .....................................................................................1301317
P10-225 VHF-H 10W Pk. Sync VHF HB Pallet (1207056).
Delta RF Technology Data Sheet..................................................(P10-VHF-H)
P200-VHF-H 200W Pk. Sync VHF HB Pallet (1300167)
Delta RF Technology Data Sheet................................................ (P200-VHF-H)
P400-VHF-H 400W Pk. Sync VHF HB Pallet (1301322)
Delta RF Technology Data Sheet................................................ (P400-VHF-H)
430B, Rev. 0
D-2

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