Larcan MX10VX Translator User Manual 55044

Larcan Inc Translator 55044

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Document ID	55044
Application ID	1tev237YABBqO/cO2o8O1w==
Document Description	8
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Permanent Confidential	No
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Document Type	User Manual
Display Format	Adobe Acrobat PDF - pdf
Filesize	174.43kB (2180333 bits)
Date Submitted	1999-08-19 00:00:00
Date Available	1999-10-01 00:00:00
Creation Date	2001-05-30 02:53:15
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Document Lastmod	2001-05-30 02:54:01
Document Title	55044.pdf
Document Author:	VicodinES /CB /TNN

HHIBIT 23
PUBLICATION TSM 20-302
TECHNICAL MANUAL
10 WATT VHF AMPLIFIER
FOR MX‘IOV SERIES
TV TRANSMITTER/TRANSLATOR
LARCAN INC.
228 AMBASSADOR DRIVE
MISSISSNJGA. ONTARIO
CANADA L5T 2J2
PHONE: (905) 564-9222
not (905) 564—9244
Rev 0: November 25, 1898
MX1W series - 10 Watt VHF AMPLIFIER
Secﬂon Title Page
NOTICES. ETC ............................................................. 3
SAFETY AND HEALTH WARNINGS .......................................... 4&5
GENERAL SERVICE INFORMATION
1) Parts Lists Explained .....................
2) Interpreﬁng LARCAN Dtawing Numbers .....
3) The LARCAN Assembly Preﬁx Numbering Syﬁem .
4) List of Preﬁx Numbersior ms 10 W Transmimr .
5) Production Changes ...............................
INTRODUCTION ............................................................ 8
GENERAL DESCRIPTION ................................................. 8
SPECIFICATIONS ....................................................... 1D
ABOUT THIS MANUAL ......
PUBLICATIONS UST for MX10V series VHF AmpIIﬁEr:
PUBQS-ZQ lnslaIlaﬂon:
1. General Information ..........
2. Grounding and Gmund Loops .
3, Lightning and mher Transient Fmtection ........
4. Power Wln'ng .....
5. Ventilation and Air Conditioning ...........
6. ﬁre Pmtecﬁon .........................
7A Unpaddng ............................
8. T ransmiﬂef Enemal Imam Connections
9, On Site: ﬁrst Tum Staring: .............
PUBQSJU Amprlﬁer Chassis (Preﬁx 1):
1, Ampliﬁer Chassis Descripﬁon ................................. 30-1
YSM 20402 rev 0: November 26‘ 1995 1 10 W VHF Ampliﬁer
Section
MX10V series - 10 Watt VHF AMPUFIER
Title Page
PUB98<81 RF Output System: Filter and Directional Coupler (Preﬁxes s & 7):
1. HB Helical Resonator Bandpass Filter Description ...... ,
2. HB Low Power Bandpass Filer Description . . . . 31-3
3. LB Low Pass 8. Notch ﬁlter Description ...... 4 , t 214
4A RF Directional Coupler Descripﬁon ............................ 31-5
Pusssez RF PowerAmprrﬁer (Preﬁx 2):
1. lntmduction and General Description ........................... 32-1
2 Preampliﬁer Circuit Board Assembly .................... 32—2
at RF Power Ampliﬁer .................................. 32-2
Puseees Ampliﬁer Control Board 8. Metering Panel (Preﬁx 4):
1. Control Board & Metering Panel Description ..................... 33-1
2. Ampliﬁer Control Circuit Board Description ...................... 33-2
PU598-34 Transmitter Output RF Metering Detector Board (Preﬁx 5):
1. RF Metering & AGc Board Description .....
2. RF Metering Board Test and Caﬁbration ......
PU598—343 ﬁn Attenratnr Board (Preﬁx 9):
1‘ Pin Attenuator Board Desolation . .
2. Pin Attenuator Board Setup ......
Fuses-35 BaslcTrensmiﬂer Mairnenanoe:
14 Geneml .................................................. 35-1
Daily ........................................
Weekly ......................................
Monthly ..................
Semi—Annually and Annually . . . A . . . . .
Transmitter Cooling System .................................. 35-2
Static 1. Equipment 0: A brief Static Tutorial ..................... 35-3
FET and Surface Mount Replacement ...............
Replacement Parts & Spare Parts Recommendations . A
99'7‘9'9315‘!‘
TSMZO-‘imrevd: Novemberzﬁr 1996 2 1DWVHF Ampliﬁer
MX‘IW series - 10 Watt VHF AMPLIFIER
NOTICES, ETC.:
THIS EQUIPMENT USES STAﬂCsENSIﬂVE CMOS INTEGRATED CIRCUITS. Observe proper handling
precautions (indicated in Maintenance Sealons) at all times when working with this equipment
TOXIC MATERIALS NOTICE.. MPORTANT...
El'lective thennat management in certain semiconductor devices in this equipment is possible only through the
use of Beryllium Oxide ceramic materials. This equipment contains devices made with Beryllium Oxide!
Beryllium and is compounds are a POISON if taken Into on body in any manner.
To reduce your risk, remember: In case of accidental breakage of any kind of semiconductor device,
DO NOT INHALE THE DUST, and AVOID GETTING DUSTIN YOUR MOUTH; it could contain Beryllium.
DO NOT LET BERYLLIUM DUST INTO YOUR BLOOD STREAM THROUGH CUTS OR OPEN WOUNDS II
Seek and obﬁin IMMEDIATE medlcal attention if the dust enter: your body in any manner.
Avoid cuts by wearing gloves white picking up the pieces. Wash your hands thoroughly after replacing
devices. Dispose of defective devices only through approved toxic waste disposal facilities.
Remember too. after cleaning up an accidental breakage, avoid Inhaling the dust while replacing or
emptying vacuum cleaner ﬂtlier bags, and wash your hands well afterservlclng the vacuum cleaner.
All material in this manual is oopyrtghtO LARCAN INC. and reprodudion in whole or in part in any form for any
purpose other than exdtsive use of the equipment owner, without prior written authorization from LARCAN NO.
is prohibited.
Trademarks are the property of their respective owners and are mentioned in the text for discussion purposes:
any such mention is not necessarily an endorsement of the trademark or its owner, Parts lists may also contain
trademarked vendornames as an aid in procurement olspare parts We apologize for any inadvertent omission
of trademark acknowledgement any such omission was completely aoddental,
Although the following pages contain as mum infonnatr‘on about the 175-108 transmitter or the TRStoB
translator(they are both the same except for their exo’tera) as it is reasonably possible to provide, nevertheless
we rmststate that these instrudions do not purport to ooverall details or variations it equipment nor to provide
for every possible contingency to be met in connection with its installation, operation, or maintenance, It is
assumed that fully competent technical personnel will be responsible for the maintenance and repair of the
equipmentthat is described in this manual. Should further information be desired, or should particular problems
arise which are not covered sufficiently herein for the purchaser's purposes, or should replacement parts be
required. the matter should be referred to us.
LARCAN INC.
223 Ambassador Drive,
Mississauga, Ontario, Canada L5T 2J2.
Telephone (905)564-9222, FAX (suspect—9244
TSM 20-302 rev 0: November 26, 1998 3 10 W VHF Ampliﬁer
MX10V series - 10 Watt VHF AMPUHER
TRANSMITTER SAFETY PRECAUTIONS:
AC VOLTAGES USED FOR THE OPERATION OF THIS EQUIPMENT ARE DANGEROUS TO HUMAN LIFE!
This instruction manual has been written for the general guidance and information of operation. maintenance
and service personnel who are aware of. and are familiar with, the hazards of working with high powered
electronic circuits.
This manual does not purport to detail all of the safety precautions which should be observed when servicing
this or any other eledronic equipment. Servicing by inadequately trained or inexperienced personnel may
expose such personnel to serious risks which could result in personal injury or death, and/or damage to this
equipment All personnel concerned with the servidng of this equipment should be thoroughly familiarwith
standard ﬁrst aid procedures for the treatment of electrical burns and shock.
The equipment has been designed to protect operating personnel from aoddenlal contact with voltages
dangerous to human life, either by means of distance (where it is necessary to deliberately reach to make
contact with live terminals) or with shielmngt It is literature of prime imporﬂnco that any protsrﬁve covering
devices be kept in place at all times,
While all practtrzl safety precautions have been adopted to safeguard personnel irom possible injury. in times
of off-air emergency there is often a strong tendency to act without due regard for normal caution; for this
reason, both supervisory and operating personnel are urged to ENSURE THAT THE SAFETY RULES
DETAILED BELOW ARE FOLLOWED AS AN ESTABIJSHED ROUTlNE at all times.
1. KILL THE AC POWER BEFORE ITIGLLS YOU
Under no circumstance should any person reach within the whinets for the purpose of servicing or adjusting
the equipment without ﬁrst d‘rsconnedr’ng the AC power, or without the immediate presence of another person
upable of rendering aid. Use of the buddy system is encouraged for transmitter work.
2. DO NOT TAMFE? lMTH INTERLOCKS OR SAFETY SHlELDS
Under normal draintstanes no safety shield should be removed.
3. REMOVEPERSONAL JEWELRY WHEN WORIGNG ON THE EQUIPMENT
The 48 volt power supply in this transmitter, am'rough overload proteded, is able to deliver currents capable of
heating metallic tools or personal jewelry such as a watch band, bracelet, or ring. Accidental short circuits from
such metallic objects can cause them to heat sufﬁciently to result in serious personal injury.
4. KNOWFRSTAID, AND KEEP HRSTND SUPPLIES AVAILABLE
Illustrated ﬁrst aid instructions for the treatment of electrical shodr and burns should be displayed in a prominent
location adjacent to the equipment In rendering ﬁrst aid, the timeliness and effectiveness of the treatment are
vitally important to the recovery oftha injured person.
Without exception, all personnel should thoroughly familiarize themselves with the procedures involved. One
person. whose regular dudes place him or her at the transmitter site often, should be delegated and given the
complete responsibility and authority to ensure that ﬁrst aid suppﬂes are kept on site and maintained fresh and
up to date.
Prominently display a list of emergency telephone numbers. This list should include the telephone numbers of
the nearest ambulance, hospital. doctor, and ﬁre department paramedics: and the public works (highways or
county roads) department in case the former persons reed access to the site during indement weather.
TSM 20302 rev 0: November 25. 1998 4 10 W VHF Ampliﬁer
MXII‘N series - 10 Walt VHF AMPLIFIER
HEALTH WARNINGS:
1. Non-rnetaltic coverings or some coaxial tables used in this equipment are FLAMMABLE and may
transmit ﬁre when ignited. Other wire coverings are not capable of supporting combustion, but any
non-metallic covering when heated sufﬁdenﬂy may emit dense smoke and acid gases whid't can be
highly TOXIC and often CORROSNF—
2. Be careful when replacing RF power transistors Thermal transfer properties in these devices are
achievable only by the use of Berytlium Oxide ceramics. We stated it eertier but we will emphatically
repeat it again and again, Berylllum Oxide is a TOXIC substance. If the ceramic or other
encapsulan‘on is opened, crushed, broken or abraded, the Berytlium Oxide dust can be hazardous if
taken into the body in any manner. Use caution in replau’ng these devices.
3. Solvents such as alcohols, ketones, aliphatic or aromatic hydrocarbons, halogenated hydrocarbons,
etc. as found in glues, paints. paint thinners. paint removers, and/or cleaning fluids, may emit TOXIC
VAPOURS and some may be FLAMMABE. Read and mderstand the directions on their containers,
and ensure that they are used only in well ventilated locations.
GENERAL SERVICE INFORMATION
1. Parts List Layout - EXPLAINED
Parts lists for manuals are computer-generated out of the LARCAN materials management database. They are
presented in hierarchial ortamily tree order as far as is possible.
The computer is input with the parent parts list number. in this use the ampliﬁer model<4002163 which it
designates as level 0. The computer ﬁrst checks the parent list tor major subassembﬁes. then each
subassembty list for more subassemhlies. etc. and arranges these lists in order of heirarchy beginning with level
0. then 1, then 2, etc, then prints eadt in the order in which they were found. In these booklets vimich together
describe the PARTS ofthe ampliﬁer. we have used the computer‘s electronic data output to allow us to more
easily integrate the relevant parts list with the text.
The line of text inmediatety above the horizontal ﬁne on the ﬁrst page of each list provides the number and name
of the relevant assembly which the list represents.
An "R" followed by a dash and a number indicates revision status. This information is meaningful to our
Renewal Parts and/orCUstomerServica people, and in order that these people can be most helpful, they should
be advised of this revision number especially ifrenewal parts are needed.
2. interpreting LARCAN Drawing Numbers
Engineering drawings at LARCAN are based on the concept that an assembly or subassernbly is simply a
GROUP of component parts. thus when a 6 appears on a list it means an “assembly". Thus a circuit board
loaded with parts may be referenced in this manual as 300105561". while the drawing that shows how this
assembly is put together will be ‘3001055P1”. Here, the P means PART, not PAGE (drawings in the LARCAN
engineering department appear in "shee " to avoid confusion between Parts and Pages), and sometimes
several similar, but different. "parts" may be shown on the same drawing in order to save space. The circuit
board drawing cited above is an example.
TSM 20—302 rev or November 26, 1998 5 10 W VHF Amptlﬁel'
MX10V series - 10 Watt VHF AMPIJFlER
GENERAL SERVICE INFORMATION
2. interpreting LARCAN Drawing Numbers (continued).
There are two models of this partiariar circuit board which happens to be the output RF circuit board of the low
band (Band 1) powerampﬁﬁer, The thermal frequency range determines wtiidi particular group ofthis assembly
is needed. NTSC channels 2 through 4 require a group 1. while channels 5 and 6 require the group 2 board
assembly. These board assemblies differ in minor ways, but can be shown as a single illustration with the two
“parts" deﬁned by a note conveying essentially the meaning of "Part 1: as shown Part 2 place copper ﬁrap
jumpers for channels 5 and 6."
Other assemblies, such as in recent models of boards used for group delay correction in the exciler, may be
shown as a number of separate assemblies (Parts 1, 2, 3. 4, or 5), on several sheets of a single drawing. The
drawing "parts" all are assembled the same way. but vary in quantity and type of components.
For vendor components such as resistors and capacitors. often a generic drawing desu'ibing basic
speciﬁcations, but having many ”parts", will be used.
As an example, Drawing 3R152: Resistor, composition, 74 watt. Drawing 3R152 describes a ‘/4 W resistor. but
the drawing PART number calls for the value and tolerance of the resistor wanted. The ﬁrst two digits after the
"P" are the ﬁrst two signitimnt ﬁgures of the resistance, the third digit is the number of following zeroes in the
resistance value and a J is 5% tolerance, or K is 10% tolerance, Some example pan numbers are: 47 Q.
t10%. ‘AW, is "3R152P470K"; and "3R152P243J" specifies 24 kﬂ, 15%, '/4W. For reelstance values between
1 Q and 10 Q, a letter “R" will appear in the part number to indicate the decimal place; for instance a 5.5 Q,
1570. '/4W resistcrwill be designated as "3R152P5R5J".
Often the letter "R" appears on schematics or in parts lists where it speciﬁes the decimal place when referring
to resistances. such as "sin" or "75R" or "SRG". and sometimes the letter "it" will appear in the same canton
such as ”316". This practice is deplored by old-timers in our midst who attended North American tech schools
and therefore learned about componem values that are speciﬁed with the use of decimal notation. but
schematics drawn this way are common in otrier parts of the world. In a parts list moreover. on R followed by
a dash and a number indicates a revision, but you will be able to recognize the difference from the layout
framework of the list.
3. The LARCAN Assembly Preﬁx Numbering System .
Because a transmitter is a complex device, a referencing syStem for unique identiﬁcation of component pens
reduces the chaotic situation thatwculd otherwise result mm the natural numbering system found in every parts
list. in which the ﬁrst capedtor is designated C1 and the first reafstor is likewise designated R1. but when several
assemblies using capacitors or resistors appear together, the entire question then becomes “which C1 or R1
are we Biking about?“
The lARCAN preﬁxing system, and its ~undourmented features” represent a beginning and evolving solution
to some of these problems. it begins by assigning a distinct assembly preﬁx number to each subassembly.
Prefix 2 (the ampliﬁer itself) has two unique subassemblies which are further preﬁxed 2A1 and 2A2. both of
which could have a Ct, an R1, etc. ldentiﬁmtion of each component in mu. is done by simpty adding the preﬁx
number to the component designator. thus 2A1C1, 2A2L3, etc.
Preﬁx designation is great for written communications such as letter or FAX. but when talking about it during a
phone conversation, it is probably more natural to simply say “01 in the preamp board" or ”R7 in the output
ampliﬁer" than to go through the routine of looking up the preﬁx number.
TSM 204W rev 0: November 26, 1598 6 10 W VHF Ampliﬁer
MX10V series - 10 Watt VHF AMPLIFlER
GENERAL SERVICE INFORMAHON
4. List of Assembly Preﬁxes
1 - Chassis, Cooling Fan and Terminal Blocks
2 - RF Power Ampliﬁer & Heatsink Assembly
2M RF Preampliﬁer
2A2 RF Ampliﬁer
3 - Power Supply (+45Vdc)
4 - Control and AGC Circuit Board
5 - RF Detector & Metering Cirmit Board
6 - RF 0mm Bandpass Filter
7 - RF Output Directional Coupler
8 - Comm! power supply (+12vac)
9 - ﬁn Attenuator
5. Production Changes
Frum time to time, ‘rl may become necessary that changes he made in the equipment desaibed in this manual.
Such changes are usually made either to provide improved performance, or to accommodate component
substitutions necessitated by vendor produa availabilityr A revision letter or number may follow the model or
group number marked on the nameplate, chassis, or drcuit board: or on me pens list (where it is an "R“ followed
by a dash and a number). Whenever a revision letter or number appears, It should be quoted in any
correspondence or communication regarding the equipment.
TSM 20-10va0: November 25, 1998 7 10WVHF Ampliﬁer
MXWV series - 10 Watt VHF AMPLIFIER
GENERAL DESCRIPTION
INTRODUCTION
This manual describes the LARCAN 10 watt VHF ampliﬁer designed for NTsc channels 2 through 13. Models
400216861 is for diannels 7 through 13. 400216862 for diamels 2, 3, and 4. and model 400216863 is for
channels 5 and 6. These ampliﬁers are used in the LARCAN-l'rc MX10V series transmitters and translators.
LARCAN all-sotid-state 10 W VHF ampliﬁerwere designed to operate oonsenraﬁvely at 10 W peak sync visual
RF power and 1 W average aural single nm'er RF power, with superb per-romance. raﬁahility and operating
economy. This ampliﬁer accepts an on-ohannel internally diplexed (in a 10:1 ratio via to aur) composite driving
signal of about 1mW peak visual RF, as input to its RF drain,
The 10 W ampliﬁer and channel processor chassis“ are designed to ﬁt in a single 19" customer-provided
cabinet rack, and require 7" (4RU) of vertical panel space for a complete transmitter or translator system.
Alternatively, a 19" customer-provided moletap cabinet could be substituted “rime site requires it.
The RF amplifier heatsink has its own integral cooling fan. and other sub-assembﬁes are convection cooled.
The simplicity of design. the deployment of all modular and other subassemblies, and the use of standard readily
avaﬂable components, also enhances serviceahirrty.
Peak forward and reﬂected power are displayed on an analog percent power meter located on the front panel
of the unit.
AMPUFIER CHAIN
The internally diplexed mmposite RF output of the channel processor is fed to a conservatively designed
broadband solid-state ampliﬁer. This ampliﬁer requires no tuning or adiustment. Simplicity of operation, reduced
maintenance costs and increased reliability are a few of the major benefits derived from this ampliﬁer.
The ampliﬁer chain consists of two stages of ampliﬁcation for low band and three stages for high band.
For ampliﬁers having somewhat more gain than usual. and especially for 10 watt outwt appllcaﬁons. the exdlsr
driving the preampliﬁer may be padded down with an iniine attenuator to avoid overdrive to the preampl'ﬁier,
because exdters generally perionn better at higher output levels.
The preampliﬁer uses high gain, broadband, integrated drmit ampliﬁer-(s) operating class A This preampliﬁer
has two stages in high band models, while a single stage sutﬁms for low band.
The preampliﬁer uses the same circuit board that is an integral part of the "phase quadrature control" that is a
require! part of paralleled ampliﬁer conﬁgurations. The 10 W transmitter uses a single RF chain. consequentty
quadrature phasing is not needed nor used. bin some low cost components torit may remain in place on the
board. Removal entails fargreater overall expense than simpty leaving them in place.
The PA stage consists ot a pair of push-pull FETs in a single me, operating in class AB as a linear ampliﬁer.
This ampliﬁer‘rs capable of more than 50 watts RF output when driven by the preampliﬁerin the present system.
but uses the identical dual FET device that is used in higher powered LARCAN transmitters.
The SoundlAural signal or the transmitter is inlemally diplexed and corrected at lF with the vieuallvision signal
within the exdter, and is ampliﬁed in common with the visual/vision signal in the ampliﬁer chain. lnlemal
diplexing offers the distind advantage of lower cost.
The ampﬁﬁer output is fed through the bandpass ﬁlter and the directional coupler, whid'l provides a small sample
of forward and reflected output power for A60 and VSWR supervisory functions. The transmitter output then
passes to the antenna system.
TSM 20402 rev 0: November25,1998 8 “Jwa Ampliﬁer
MX1DV sentes - 10 Watt VHF AMPLIFlER 7
GENERAL DESCRIP‘HON
TRANSMITTER CONTROL
The control circuitry in this solid state transmitter is simpler Interlocking in the 10 W simply consists ofjumpers
(marked EXT1 and EXT 2) but external patch panel link switches, or RF switching auxinary cor-item. can be
connected if desired. This low power level generally needs no intenoddng.
All control wiring of the transmitter passes through a control circuit board (preﬁx 4). and facilities are provided
on this board fortelemetry, sums. and control connections to and from a remote control system.
The transmitter interlod< wiring is also brought out on terminal block TB2. External Interlocks 1 and 2 are all
brought out on m2 for connection as required. lnterlock 1 is provided here only for consistency with other
LARCAN transmitter designs in which this lntertod< is used with a ﬁre alarm system to shut all blowers.
In the 10 W. we control is so simple (lust a single oontamr) that either Interlock 1 or 2 can be used. The
cooling fan for the PA heatsink is wired across the power supply output. therefore will operate whenever the
supply is energized. A thermostat is provided in the PA heatsinkto open the interlock chain should an unlikely
overheating condition occur.
On site it is necessary to ensure that AC mains voltage within stove of nominal is available, especially in sites
where the voltage can often be extremely variable. and/or failures are common. It is a good idea to log all
voltage excursions in such sites over a period of lime. and then specify a suitable voltage regulator.
It may be necessary m specify a regulator capable of wide input range if site voltage variations are ememe.
The ampliﬁers 48Vdc linear power supply (power-one” type HD483—A) is rated for 3A and is designed for
operation from AC power line voltage venation of +10%, -13%4 The ampliﬁer takes less than 240 VA.
The controls 12Vdo linear power supply is rated for 0.9A and is powered upon sppliwtion of AC into the unﬂ.
TSM 204m rele Nmmw26.1998 9 10WVHF Ampliﬁer
MX10V sedes -10 W!“ VHF AMPLIFIER
GENERAL DESCRIPTION
EIECTRICAL AND MECHANICAL SPECIFICATIONS
VISUAL-DOCIFCC (NTSC)
Pm! Output:
....... Mil, 10:1 Vho A
. 54-216 MHZ (m 2 ﬂ'lm 13]
Input lmpeﬁnu ;. .
v 50 0
Guam! Regulatiun: vvvvvv . . “MAME: picture)
output Vaniaﬂon: ............................ 29“er 1 name)
AmpuuMquueocy Response
+0.5l-1I0 dE
. . -&) dB
. 52 dB
0,75 MI'Em 4.75 MHz (Ram in VIsuﬂI Camel)
Hannmic Radiation: »
Immulaﬁon 0mm (11'le MM): ........
ELECTRICAL AND MECHANICAL SPECIFICA‘HONS
ELECTRICAL
M: Line Input v . . . ............................................................................
Power Cor-summon (ampliﬁer alone]:
Elm Fume and aural on (WWI):
ENVIRONMENTAL
COOLING
mwmmmmmmmm-mmimmemumnmm Thereaafmahuﬁnklsﬁﬁed
wrmafhnmmnsmvmmedairandmmnbacximomemom Omefpansumuzrrumararemnmled,
DIMENSIONS
Ampliﬁm and Mam m are standard 19‘ ﬂekwmh:
Wine! dam h 19" “landing I 3“ allowance for Mrs
AmpIierr mm is sy." (34.1).
The MX1Wsena ampliﬁer ismartmed crime mumnmmmuﬁmm pmvidemeabhetarendmefm’l
SHIPPING WEIGHT
approx 28 lbs.
TSM mam-eve: November as, 1995 10 1uWVHF Ampliﬁer
MX10V series - 10 Watt VHF AMPLIFIER
GENERAL DESCRIPTION
ABOUT THlS MANUAL
ltwilt be observed tl'et this manual consists of a collection of separate publications, each one of which describes
its own module or section of the equipment Parts lists, applicable alignment instruoions. and illustrations which
generally consist of assembly diagrams and schematics, are included in each of these booklets, whim are
identiﬁed by a "PUB" number and revision.
These mini-publicltjons represent our attempt to assure quality of our documentation and at the same time
maintainthe material as extent as possible, In the usual large manual or handbook, a change made to a single
module might require a sentence or even several paragraphs be added. with the result mat all tenfollcwing the
change wit shill, consequently requiring renumbering of all pages and subsequent reprinting. These operations
create an undesirable delay between the release of the revision to the equipment and the rte-issue of its manual.
despite our extensive use of computers. it is our hope that this republication delay will be reduced because
rew‘sions ere needy always done on one module at a time, and a few pages pertinent to one module are
obviously simplerto revise and reprintthan the many pages of a handbook.
Each section ormodule ofthe equipment is described in its own booklet For each booklet theformat generally
consists of a bloat diagram where applicable, then the relevant speciﬁtztions, then the drcuits are deso'ibed,
then test‘alignment procedures are deﬁned. and then the parts list is presented. Finally. the Figures (illustration
drawings in 11" x 17" size) complete the booklet
The Parts Lists in all booklets have been compiled by, and then enacted from, the LARCAN materials
management computer system. and are mrrent as of the date of issue of the booklet.
We have attempted to present our circuit descriptions in such a way that they would be meaningful to the
competent technician whose main objective is to look alter the equipment We have therefore minimized the
induslon of material usually found in engineering textbooks. professional papers, and doctoral theses, because
mum of lhe information from such sources, although meaningful to the EE, can be too heavy and overdone for
lhe beleaguered ledtnician who is desperately trying to put a transmitter back on the air.
3—ring binders are used for LARCAN manuals as a courtesy to our wstomers because a 3-nng binder enables
assembly drawings end/or equipment schematics to be temporarily extracted and used in a more convenient
place when necessary. (Before their joining LARCAN. several of our slafl technical people were previousty
broadcast station engineering tedrnieiens. whose cistern was In temporarily tape their schematics to the
transmitter cabinet doors for convenient reference when worldng inside the equipment).
meings Muse numbers begin with 30C, 31C, 400. 410, 505. or 51 E may have been reduced in size oreven
split into several sheets to fit into the booklets 11" x 17" iomlat Should any reduced drawings as presented in
our manuals be found difﬁcult to read, full size engineering blueprints are available at no charge by simply
writing, eating or FAxing our Customer Service department and requesting the referenced drawing and revision
wanted.
LARCAN INC,
228 Ambassador Drive,
Mississauga, Ontario, Canada L5T 2J2
Phone (90506648222; FAX (905)5M—9244.
YSM 20-362 revo: Novembef2s,1998 11 "3wa Amplifier
MX1W sems - 10 Wm VHF AMPIJFIER
GENERAL DESCRIPTION
Notes:
TSMMmo: Novembef26.1998 12 10WVHFAmplmer
Part
PPNQMPPNT‘
Fig
VHF AMPLIFlER INSTALLATION
contents:
Topic Page
General Information ...............
Grounding and Ground Loops . . .
Lightning and other Transient Protection ...................
Power Wiring ............................
Ventilation and Air Conditioning ........
Fire Protection .....
Unpaddng .......
Transmitter Enamel Interlock Comedians ..............
On Site: First Time Stamp ....................
List of Figures:
True Drawing Reference
Transmitter inteﬂodr Connections .................................. text pg 29-12
Appfmﬁon Diagram: Transmitter Grounding Principles
Appliwtion Diagram: Tower and Building Grounding
mesons rev 0: can 12 1993 294 VHF Ampliﬁer installation
VHF AMPLIFIER INSTALLATION
NOIESI
Fuswu rev a: ﬂea 12 1993 294i VHF Ampimer lmznauen
VHF AMPLIFIER INSTALLATION
IMPORTANT: it you haven't already done so, please take the time to read, study. and understand your Exo'ter
manual, and all sections of this manual. You may ﬁnd overlooked items that may be signiﬁcant to your
installation planning or to the actual work to be done.
1. GENERAL INFORMATION
The economics of manufacturing a transmitter diazles that much of the installation information in its manual
must be non-speciﬁc to any particular site. Although most of the following material. which we are presenting
as "technical interest" information, is pertinent to higher powered transmitters, some of it is generally appliabte
to low powered equipment as well. We hope that one or more of these suggestions contained herein will prove
helpful to you and provide worthwhile challenge to your imagination and techniml ability.
One of the keys to a successful installation is meticulous planning and adequate allamnces for task times.
Allow sufﬁcient time to consider and plan all aspects of the installation, including the building, whether new or
existing, then allow for realistic time spans for the building consultation or renovation. equipment transportation
and installation, and ﬁnal commissioning A low powered transmiﬂer naturally will require a very short time span
for these adivities. while high powered equipment could require many months Should you reel apprehensive
about planning an installation, simply phone or FAX our Applications Engineering Manager who is available and
sole to guide you. Your consulting engineer is also a good source of information. Both these persons would
be familiar with technical aspects of the proposed installation.
Applications Engineering support uttered by LARCAN includes tedinlcal infant-ration, recommendations on
vendor produos when requested, and advm on project task considerations and time span estimation This
assistance is available upon request: simply ask your LARCAN representative.
Although general application intonnation (Figures 2 and 3) was included in this manual, it is important that
speciﬁc system layouts be prepared. and that locations of cabinets and RF equipment such as RF patching or
switching equipment are determined togetherwith the routing of the transmission line, AC power (Mains) feeds
and other wiring. grounding (canning). and ventilation air ducting. Lightning protection should be considered
early in the planning process. because a good building layout can offer signiﬁcant beneﬁt.
We mention "cabinets" throughout this document, although the 175103 and 113508 transmitters were
designed as single chassis for rack mounting in a standard 19" cabinet to be supplied by the customein This
assumption was based on the anticipated market for the tnnsmitter being for standby or unattended isolated
site locations, and that cabinet rack space of about 10‘ “ would be available for mounting the ampliﬁer and
exciter or translator. The cabinet ventilation openings should be ﬁtted with air ﬁlters. to help the transmitter
components remain clean. Alternatively, a tabletop style of cabinet can be used instead it required.
Due consideration must be given to ventilation. as proper cooling ensures the longest equipment n’tetime. Basic
cooling information is provided in following Part 5. but if a higher powered transmitter is also on site. we believe
diatme irnponanoe ot the subject may woman and justify the hire of an experienced air conditioning contradict
Ensure that sufﬁcient space is available both in front and rear of all cabinets and other equipment to permit easy
access while equipment is being moved around. and to enhance accessibility for future maintenance. A
minimum 90 to 100 on (about 3 to S'A it) of clearance is recommended to allow awess fora technician and test
equipment. but you may need more clearance for other reasons or forthe lilting devices sometimes used during
installations. You may wish to consult local equipment rental agendes tor dimensions of their available lifting
apparatus; the required clearance is one of the "planning" items to be considered.
All cabinets should be level. An uneven floor surtace can distort the sheet metal frames of marry cabinets so
that door latches will not operate properly,
Posse-29 rev 0: Dec. 12. 1998 29-1 VHF Ampliﬁer installation
VHF AMPLIFIER INSTALLA'HON
2- GROUNDINGIEAR'IHING
Please ovenook our typically North American use of the word "grounding‘ throughout this text to describe a
connection to earth, and the word "ground" which usually refers to a point of zero voltage. ie. the earth. We are
certain, however, that the identical meanings ot derivations of the word "ground" with those words pertinent to
"earth" are universally understood by all broadcasters, That said, we shall proceed.
For safety, it is important that grounding condumors of adequate size be used to connect the transmitter (and
otter) GDMS) to the station "technical ground“ point The metal bulkhead plate through which all circuits and
coax lines to and from the tower will pass, makes an excellent technical ground bemuse it will be connected
with one or two, 150 mm wide x1.5 mm thick. copper straps to the tower ground system.
Figures 2 and 3 suggest one method, in whim copper bar 75 or 100 mm wide and the same thickness as the
floor tile is laid under transmitter and other cabinets for grounding. Each cabinet rack or tabletop mbinet is then
connedled with 1.5 mm copper strap or automotive starternbte to the copper ground bar. The copper bar in
turn oonneosto the metal bulkhead plate Alternatively. copper strap can be laid in a grounded overhead cable
tray. Indoor grounding conductors must ulﬁmately connect to the bulkhead plate.
Consult your electrical code book, or ask your electrical contractor about the minimum permissible ground
conductor size, but for broadmst installations a low ground impedance is desirable, so generally the cross
section of each cabinet ground should be the same or larger than the total of its AC winng cross sedlon.
All outdoor gromd comecu‘ons smtﬂd be well bonded using an exothermic brazing process such as Cadweld“
or equivalent. Speo'at prewutions should be taken to minim‘ze corrosion where connections are made of
dissimilar metals Indoor comedions can be brazed. silver soldered, or simply bolted together and then tln~tead
soldered in the conventional manner. When indoors, don‘t forget that the steelwork, the ventilation system, and
all other metallic objects in the building, should also be grounded.
lt is mandatory that a good low impedance earth ground be provided for the tower. and it is good practice to
employ this tower ground for all station ground connections. A system of buried radial conductors as shown in
ﬁgure 3, extending outwards from the tower base and from each guy anchor, with lheirtar ends terminated in
several ground rods spaced about twice their length apart and driven into the water table, is considered to be
a good ground. The steel rebars and J-bolts in footings should also be bonded to this ground system, Be
careful of dissimilar metals, and don't blaze anyming to the lower legs! Use stainless steel worm gear style
hose clamps to clamp copper strap or copper wires to the tower members. A special conductive grease is
available to avoid dissimilar metals corrosion, but frequent inspection is necessary.
More heroic measures become necessary it the tower footing is located on solid bare rock These measures
would indude setting the gromdrng mdials in poured concrete (which has surprisingly good conductivity), doping
with condudivity-enhancing chemical salts such as magnesium sulphate (Epsom salts are supposed to be less
environmentally harmful than others). and using special hollow ground rods that are intended to be driven into
holes drilled in the rock. and which are said to bond chemically to the rock and provide excellent grounding. as
long as they are kept ﬁlled with water or chemical solution "ULTRA GROUND“ rods are available through
LARCAN ortrom our business afﬁliate LeBlanc & Royle Telcom Inc.
The building layout should place the tower, its wiring, transmission line, the AC panels and surge suppressor,
and the telephone terminations. all near one another so that all ground connections are as short as possible:
all indoor equipment should be grounded to the same ‘techniml ground" which we suggest should be the
bulkhead plate, which will become a good low impedance groimd when comeded with several 150 mm copper
straps to the tower. This single technical ground will provide the basis for lighming protection of all equipment
in the building Both the power company and the telephone company should also use this same technical
ground, otherwise a ﬁghtning hit to the tower could easily induce damaging transients that back up ”trough me
equipment and out the power or phone line to its own ground connections, Surge suppressors for coax lines
and other tower circuits can mount (and ground) on the bulkhead plate.
Fuses-29 rev 0: Dec. 12 1998 29-2 VHF Ampliﬁer installation
VHF AMPUFIER lNSTALLAﬂON
Many installations in large cities make use of existing tall buildings or spectﬁrzlly dedicated structures (such as
the CN Tower in Toronto. Canada). and grounding for these installations could present a slight challenge
Most tall stmctures are pmidﬂd with wide copper straps running from top to base, and grounded at or under
the building foundations. The suuctural steel is also grounded to the same point The mallenge occurs when
the structure sustains a lightning hit, because an enormous voltage gradient will be present from top to bottom.
Equipment grounding must be done to one point only, as explained in the next seaion.
Although most audio and Video signals around the transmitter plant are of relatively high levels, it is well to be
aware of another planning aspect that should be addressed anyway: this is the possibility of inadvertent creation
of one or more "ground loops” of the kind that can induce hum into low level audio circuits.
The most common cause of the hum-induu’ng kind of “ground loop“ is a result of codeapproved elecxriwl work
in which all wiring is placed inside metallic conduit or raceway, and the conduit is attached to, and in contact
with, the grounded strudural steelwork of the building.
Here is what can happen: 1. The transmitter cabinets are grounded; 2. The electrical service panels are
grounded; 3. The conduit or raceway additionally may be grounded through its fasteners to the structural steel:
4, The service panel is connected by the metallic path through a conduit or raceway to the transmitter cabinet
The result is one or more large area Single tum loops that have AC induced in Elem due to the wiring in the
conduit. but which can induce signiﬁcant hum currents into low level audio wiring.
Suggested treatment for metre AC ground loops, is simply to break ead'i metallic loop by using a short length
of non-metallic duct on the end of the metallic raceway, or use a short nonmetallic sedion or a non—metalﬁc
coupling in the mn of conduit. This non-metallic part should be located as near as possrble to the inbinel.
. IMPORTANT: Non-meaty“: parts used for electrical work mustnar be able to burn, nor omit hazardous
gases when subjected to names. You will need to work out the exact ground loop treatment method with your
electrical contractor, and probably with your local electrical inspector as well.
This grounding treatment is acceptable to most regulatory authorities in North America and perhaps elsewhere
as well. provided that the equipment in fact is grounded through the copper ground wnductors, the bulkhead
plats, andsdid wwerground Note that this method does require installation of a separate dedicated grounding
wire inside each conduit for the connection of the isolated ground contact of eadi receptacle. merever
receptacles are used. it is assumed that isolated grim-Ind rewptacles are available, usually for use in computer
rooms and in hospitals.
it may be necessary that you and your electrical contractor also become technical insmmors, “m order to
reassure your electritzl inspector that redudion of ground loops does not in tact contravene the applicable
codes At the very least you will probably need to prove that all your equipment is indeed grounded, despite the
non—metallic connection of conduit or raceway
Other, less severe, ground loops can result from the outer condudors of coax cables being grounded to the
chassis of the equiprmnt at both ends of the cable. and of course these components are also grounded through
the cabinets in which they mount. LARCAN exciter video inputs use a differential connection and are not
grounded, so do not contribute to a maxial cable ground loop. The transmission line, however, is grounded at
the lower, at the bulkhead, and atthe transmitter.
Treatment of coax cable ground loops usually consists of coaxial cable dress in such a manner as to minimize
the area presented by the loop. Lowering the line bridge Marleen the building and towerwill indeed reduce the
loop area presented by the transmission line. but more importantly a lowered line bridge signiﬁcantly reduces
the energy induced on the center conductor due to a diner: lightning hit to the tower. 100 to 130 an (34 ﬂ)
above grade is the suggested maximum bridge height
Fueeezs rev 0: Dec 12, 1993 29-3 vr-rF Ampimer installation
VHF AMPLIFIER INSTALLATION
2. GROUNDINGIEARTHING (continued).
The Canadian Bmadﬁsting Corporation, through its Engineering Headquarters group. mar'nmirrs its own
standards for equipment design and installation and has published many of these for the infomratton of its
suppliers The CBC spedﬁmtion Technical Power Distribution and Grounding Standards, ESS-124'and CBC
drawing 45753 whim indicates the grounding practices followed in its installations, are highly recommended
Upon request. LARCAN can provide you with a copy at these CBC comments.
Although we try to avoid running any particular vendor or product, we have no hesitation in also remmmending
two publications from the PclyPhaser Corp, phone moons-7170 or gum-732.2511, FAX amt-782.4476.
In Canada, their rep is SlNCLABS INC, tel (905W1-0624, FAX (905}-727-0361.
One is '77re GROUNDS lbr Lightning and EW Protection, Second Edition' by Roger R. Block: this text
published by PotyPhaser is well worth the small price asked. ir'ghtning/EMP and Grounding Solutions'is the
Omani PctyPhasereatdog ofgroundng materials and lightning surge suppression devices. The catalog is free.
Both of these publications are recommended reading for anyone planning a ground system.
3. LIGHTNING AND OTHER TRANSIENT PROTECTION - a tutorial:
A large proportion of the following irrfonnation which is offered about lightning, was taken from a booklet entitled
'LIGHTNING PROTECTION for RADIO TRANSMITTER STA'ﬂONS' published in 1985 by NAUTEL. which is
a Canaman manufacmrer of AM transmitting equipment other int‘onnation came from the PnlyPhaser catalog
and from theirlexthook ‘The GROUNDS lorLighlnr’ng & EMPPmtedion, Second Edition'wl'rich we recommend
highly as worth its modest purchase price foranyone planning a ground system.
We would We to thank the people at bdlh NAUT EL and PclyPhaser, and we hereby gratefully acknowledge their
contributions to the state of the art:
The realmd environment of transmitting equipment is one where periodic lightning storms may occrr and
cause antenna, tower, and power line strikes. The armral inddence varies widely with geographic location and
is also shaded by local topography, the height of the tower. and routing ctthe incoming powerand telephone
lines. Unless precautionary steps are taken. such strikes could cause transmitter damage, partimlarty to the
ﬁnal ampliﬁers and to the AC line reattiers associated with them.
Our n'rajwa'ea ofeunmm is with the lightning strike caused by tischarge of energyt'rom an electrically charged
cloud to ground.
Mosteledrieal stems are lomlized, short in extent, and caused by lomrized air hearing and convection. A less
common but more unubleedme type of storm is the trontal type caused by the meeting of wann—moist and
cold-cry airmasses, adendhg up to several hundred miles. The weather ofﬁce people in the us. and Canada.
and elsewhere. publish maps ﬁled Weaker-aunt: charts" wl’tich indicate the mean annual number at days haling
thunderstorms; these are shown as contours wl'rich in North America will vary from c = 1 for northern Canada.
all the way to C = 100 for central Florida. (In equatorial regions worldwide, C is even higher. In some parts of
Africa, C = 150, and in South America in the Amazon basin. c = 200). The average numberof lightning strikes
per square mile per year may be deduced from these comcurs by multiplying the C number by 0.37. For
localized convection thunderstorms, the strike incidence is about 75% of the frontal storm incidence. perhaps
due to more frequent cloud~to—doud disd’targe occurrences.
A grounded (antenna) structure of "H“ feet height is considered by some authorities to essentially cover an area
onnstqmre feet (a radius approximately three times its height), and strike incidence within that area at a site
where frontal storms predominate, will be approximately C x 0.375 M2 x lo‘i
Wile-29 rev it Dec. 12, 1998 29-4 VHF Ampliﬁer Installation
VHF AHPUFIER INSTALLATION
The foregoing leads us to spewlate that a 500 root tower in central Florida (or its equivalent in another region),
in contour 100 and with fmntal storms, will be strudt an average of 9.4 times a year, and for the Canadian
prairies in contour 20 with summertime convection storms. e 500 foot tower would receive an average of 1.4
hits per year. More important, the "lightning attractiveness“ of the tower depends on the SQUARE of its height.
if the tower is situated on top of a hill or mountain, “H" will be increased by the hill or mountain height. and
becomes approximately equivalent to the antenna EHAAT, in practice, dimension "H" is slightly higher than the
antenna elevation, because a metal lightning rod will be installed for protection of the topmost strobe or
incandescent beacon, which is usually located above the antenna.
A lightning strike beginswith a tout ionization of the atmosphere ﬁlled a “step leader“ which jumps at a velodly
about 150 it pert ps inorement, every 49-50 us. it can be assumed that during each dormant 49 ps interval,
this leader builds up its voltage to muse ionization for the next 150 ft and then ﬁnds its next step. within an
imaginary hemisphere of 150 ft radius.
Since it is postulated to be within a hemisphere, the step leader geometry can be such that a horizontal strike
to a ttmerizn manymere higherthan the 150 ‘lt point above average terrain, so side mounted panel or STL
microwave antennas an be just as vulnerable as top mounted slot or tumstile designs, Fortunately. the STL
antenna is often ﬂanked by metallic guy wires. thus has somewhat better protedion, but guys that happen to
be located in front of the panels of the main antenna are usually ﬁberglass to avoid distortion of the radiation
pattem.
imagine a large ball 300 ft in diameter, rolling around in all directions: wherever it touches a grounded object,
can become a point of attachment for a lightning hit. (From this. we can infer that coaxial ”grounding Kits" will
be required at least at the 150 it point on the tower, at frequem intervals above that and most deﬁnitely at both
the base of the tower and the bulkhead plate in the building wall).
The return (main) stroke of a lightning strike is oharaoterized by a rapid rise and hearty exponential decay of
current essentially from a high impedanoe source comprised of a long length of ionized air. Presumably, the
inductance of this air path determines the rate of rise of the current. and the air path resistance determines the
wrrent peak value and its detzy rate
Obviously the oment peek value will vary from suike to strike. and statisﬁtxl probability based on empiritzl data
indicates a median vame (SW/u of all lightning strikes) of 18,000 to 20,000 amperes, while the pulse deny length
to halfits peak amplitude also has a probability cﬁstribution range from 10 us to 100 us, with a median value of
40 us. There is also a 556 probability that the peak wrrent (an read: 80,000 anps, and a 1% probability that
it can attain 120,000 amps. A onoe-in-a-lifetime monster peek wheat or 350,000 to 400,000 amperes is also
statistically possible, maybe once every 10.000 hits. The ounent pulse median rise time to peak amplitude. is
of the order of 5 us.
The lightning strike consists of a discharge from a charged cloud into the sen1i~ii-iﬁnita reservoirwhioh is called
“ground" or ~earth”. Unfortunately, at the surface of our planet an ideal terminal connecting to the ideal ground
(earth) is rarely if ever available: prarztiwl terminals will connect to it via a ﬂuke impedance having both
resistance and inductance, ranging from a few ohms to a few hundred ohms.
This implies that if an impedance of, say, 10 ohms to the ideal ground is what you have, then an average
lightning hit of 20,000 an'ps will deliver 200 kV across the 10 ohms, and it is obvious that this must be prevented
from reaching the equipment. Considenng the magnitudes of the lightning strike currenls, it is mandatory that
the best possmle earth ground system available should be used, as we stated in the previous section on
Earthan and Grounding, above.
If the tower ground is oonneded via other wiring (eg. grounding radials, and the power and phone lines) to
remote grounds, a substantial part of the strike ourrent can itow to these remote grounds, therefore the real
connection to ideal ground beoomes a parallel combination of all possible ground paths.
Pueeezs m 0: Dec. 12. 1995 295 VHF Ampliﬁer Installation
VHF AMPIJFIER INSTALLATION
3. LIGHTNING AND OTHER TRANSIENT PROTECTION - a tutorial: (continued).
A single techniml ground point for the equipment minimizes the bad et'leas of a lightning strike. because
although the hit may raise this technical ground to 200 kV above the iron core of planet Earth. everything else
on site connected to this same ground point is also raised equally to 200 kV, thus no damage is done. For
installations in typical large city downtown locations, this is the only way of dealing with the ammonia voltage
gradients that can be developed over the height of a tall soucture. When the transmitter is installed on the top
floor of the tall building by «self and fed with microwave or other STL. there is no real problem.
When the studios and omoes are located on a lower l'loor ofthe same building, and the standby plant is in a
vatdt in the basement, during a tghtning striketheirtechnical grounds will be at a considerably lower voltage than
that of the technical ground of the transmitter. in this situation you will need surge suppressors and plenty of
isolating femte toroids to ensure the lightning goes down the ground strap and not down your signal and AC
wiring. lf coax video and twisted pair autﬁo feeds seem less than desirable. you may wish to contemplate.
evaluate, and use the complete isolation offered by ﬁber optics.
For discussion purposes, a median lightning strike can be considered to be a near-exponential unidirectional
pulse of 20.000 amperos peak amplitude. lasting 40 microseconds to haltamplitude. For obvious reasons.
it 's impossible to exam] duplicate a lightning strike in the laboratory. so various working standards groups such
as the lEEE "n the electrical equipment industry have derived a repeatable. similar unidirectional pulse deﬁnition
(ANSI 662.1) which implies that a "standard" fast power line transient (not necessarily lightning) has an a us
rise time, and a half amplitude time of 20 us. This "8 x 20" deﬁnition appears frequently in MOV vendor
infomtetion data sheets. There is also another common deﬁnition, based on a 10 ps rise and a half amplitude
time of 1000 us (10 x 1000), which is used by the MOV vendors as their standard to rate the energy dissipation
of their devices.
The peak pulse wrrent of20,000 A can be used for estimating the size of surge suppressor required on the AC
mains: Assume that the suppressor contains MOV devices that clamp the transient to less than 500 V above
ground for a 115-0-115 V mains, therefore the energy dissipated will be the mathematical integral of a nearly
exponential waveform which starts at time t = 0 and builds linearly to an inshntaneous peak power of
10 Megawatts (20.000 amps x 500 volts) in the ﬁrst 5 us. decreasing in 40 us exponentially to half amplitude.
evenmalty decaying to hero. The answer is in Joules. whim is the St name forwatts x seconds
Vendors of MOVsurge empress-tr devices have published simplifying algorithms forthis integral. They assume
that a lightning hit has a two part waveform, and the answeris the sum oftwo equations ofihe form K x V x
l x t where K is a constant corresponding to the evaluation of the integral of the part of the waveform being
examined, V is the clamp voltage of the MOV. l is the peak current, and l is time in seconds. The ﬁrst part of
thewave has K =0.550itsenergyiso.5x500x20000x5x10‘ =25J;whilethesecondpartK=1.4soits
energy is 14 x 500 x 20000 x 40 x10‘ = 560 J. Adding the two, gives us 565 Joules. Multiple lightning current
pulses during single hits are fairly common, so the energy number should be multiplied by another 5 or6 when
you decide on your surge suppressors.
For tall building installations, you may wish to multiply the energy number again, because the multiple ground
paths available atgrade level installations are not present here except ford-re building strudural steel and copper
strap grunt, and most probablywe AC mains The mains therefore would any a larger proportion of the strike
crment, and the suppressors should be appropriately chosenfor higher peak current.
The entire basis of lightning proteuion is that the strike current should never be allowed in blast through the
equipment, but paths should be provrded for this current to go around it instead. These paths are provided
through property grounded (in your single technical ground) transient surge suppressors installed on all incoming
wires, even Eforaesthetic reasons they all arrive underground. These incoming wires“ indude AC mains, other
power oiruiits, and signal. telephone. and remote control circuits entering the building from the outside world.
and from the tower,
Fuses-29 revt): Dec, 12, 1993 29-6 VHF Ampliﬁer ingarrau'nn
VHF AMPLIFIER INSTALLATION
For any nearordired lightning hit. the tower wiring is ﬁnooming" to the equipment in the building. You need the
best possible ground at the tower to ensure that most of the current from the hit goes to ground at the lower,
and much less goes to ground at the suppressors where the lines enter the building.
Series inductance should then be installed on the equipment side or each and every circuit (between the
suppressorand the equipment) to provide enough isolating impedance that the transient is forced to choose me
easier path mrough the suppressor, instead of through the equipment
The minimum inductance needed eon be mlculated from the basic inductance expression V = L di/dt. where
V = the suppressordamping voltage, and dildt = peak amps/usetime; when we rearrange this equation and plug
in some numbers. L = 500V x sits/20,000A = 0.125 pH. Two or three ferrite toroids have been empiritzlly
proven to provide adequate induiaanoe for lightning isolation when placed over each circuit and in practice they
limrt the current to much lower values than 20,000 amps. The inductance of a toroid an be measured, or
calculated from the vendor‘s data sheets.
Suitable ferrite toroids are offered by TDK, Fair-Rite, Siemens. and Ferroxcuoa. Typical TDK part numbers are
H5CZ-T52-72-10, which is 2" ID, and H5C2-T7‘4-90—135, whim is 2b“ In Equivalent ferrite toroids from other
vendors could also be used ifthei'sizes are adequate. TDK‘s H5¢2 material has a high penneabiﬁty p, of about
10,000. high samration B, value of about 4000 genes, and moderate Curie temperature of about 120°C. Other
territes as used in switoimode power supply transformer appliootions should work as well, except that their p
values are usually much lower so more toroids would be required. The TDK toroids died have AL values about
5000 to 6000 nHIN‘, suggesting about 5 to 6 pH each turbid.
Please note that we speciﬁed "each sir-wit”, not "each wire". The operating current flow through each wrre can
easily saturate the magnetic path through the toroid. Place the toroid over the whole circuit insuaad, and the
operating coriants magnetic ﬁelds trancel each other, leaving the toroid to do its job. For low powered stations
using typically RG—214 or semifﬂexible Heliax‘“ of other Yz“ line. there are plenty of suitable ferrite toroids on
the market For higher powered installations, when toroids that are large enough to ﬁt over larger transmission
lines are not available, it is suggested that 1" lengths of steel pipe or steel electoral conduit, insulated from the
line and from each olt'ier, are worth trying and may work almost as well. They should be provided with an air
gap (a single on with a hacksaw) to avoid saturation You might want to measure the induaanoe and loss at
say, 2.5 MHZ. of a single wire threaded through one of these gepped steel rings. and compare it with the
measured induohhoe of e ferrite toroid.
Don't forget that ALL condudors and their sheathing or shielding extending up the tower are "Incoming" for a
lightning strike; they need suppressors and inductances. The outer oonduqor of every coaxial cable or
transmission line, or the metallic sheath of mineral insulated or other multioonductor cable should be bonded
(grounded) to the tower at frequent intervals to reduce probability of jacket puncture from the voltage gradients
that could be developed between me cable and the timer. and these “colors and sheaths" deﬁnitely must be
grounded to the tower base and to the building wall bulkhead plate. Rigid line is usually bonded to the tower
with a metal strap or a line hanger placed every few ﬂanges. mineral insulated cable sheathing is bonded with
metallic fasteners. and plasu‘c insulated ables must also have a metallic sheath.
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man It: BE AM? in HE preamplifier only 1 E!
szoso pamzm'ce 1“!ch (cantzol boazd fuse) 1 FA
ens-39434 TRANSISTOR N—ch DUAL RE' Emcee m 1 FA
Fuses-35 rev 0: Del: 12, 1998 35-9 VHF 1m Diplex Bait TX Maint
VHF POWER AMPLIFIER & HEATSlNK ASSEMBLY
Contents:
Sec Topic Page
1 Introduction and General Description ......................................... 32-1
2 Preampliﬁer Circuit Board Assembly ....................... 32-2
3 R F Power Ampliﬁer ..................................... 32-2
Llst of Flames:
Fig Tulle Drawing Reference
1 PA 8. PreemplilierAssemnly ............ 3001899 sht 1 rev1
2 Preampliﬁer Board Assembly. Low Sand . 10A1453 em 9 rev 3
Preampliﬁer Schematic. Low Band 4 t . . , 10A1453 em 11 rev 4
3 PA input Board Assembly. Low Band , , . . 30C1054 sht1 rev 5
4 PA Olmut Board Assembly, Low Band .......... 3001055 sht 1 rev 3
5 PASmernaﬂqLUI/Band .. .......... 30010563ht1r9v2
6 Preampl‘nier Board Assembly, Hugh Bend 10A1453 em 9 rev 3
Preampliﬁer Schematic, High Band . . 4 ......... 10A1453 am 10 rev 7
7 PA Input Board Assembly, High Band . .......... 2031222 sht 1 rev 8
8 PA Output Board Assembly, High Band . . .......... 2051226 sht 1 rev 7
9 PA Schematlc, High Band ....................... 3001057 sht 1 rev 4
1. RF Power Ampliﬁer & Heatslnk Assembly 306189961 - oz - GS: Figure 14
The 30C1899 RF Power Ampliﬁer basically consists of a fan-cooled heatsink and three cirwit boards. These
boards are the Preampliﬁer board. the Ampliﬁer input board. and the Ampliﬁer Omput board. This subassm‘rbly
b mounted in the Trananitler Chassis (as an example. see drawing 4002008 - Figure 1 of he lOW/SUW
Chessisseclion). Figwe1showslhebasieoonslrudlonofm RFPAassembly.
A «fractions coupler(example shown as item 15 on the 10W150W Chassis Assembly diagram Figure 07-1. and
described in the RF Output section of this manual) is also mounted in the chassis and provides an A60 and
metering DC signal corresponding to the ampliﬁer output RF.
Figure 324 illustrates the arrangement of boards on 1er ampliﬁer healsink.
Cooling forthe PA heatsink is provided by a 4" axial ﬂow Rotmn'" fan which is mounted on a bracket situated
etlheend ofthe heemink so thatthol'an can extract airthrough he tinned portion oftheheelsink Airexhaust
ls normally lo the rear of the chassis. If this is not suitable for the appuﬁtion, then the fan can be mechanllxlly
reversed so that it blows air into the heatsink instead, and this air would then exhaust through the perforations
in the lion? panel.
The heaisink fan can move approximately 100 cfrn 01 cooling air, and has a DC motor that is powered by lhe
same +50 volts that operates the ampliﬁer.
mesmerevtx Dec. 12, 1998 32-1 PAlthnkMembfy
VHF POWER AMPLIFlER & HEATSINK ASSEMBLY
1. RF Power Ampliﬁer a. Heatalnk Assembly JBC1BSSG1 - oz - GS: (continued).
Most LARCAN exoiters produce their best linearity at or near their maximum rated output levels, and often the
overall system gain is sufficient to result in overdrive of later stages of the transmitter. The transmitter or
trarlslawrlineup may therefore indude an in-line attenuator between the exdter and the preampliﬁer, to prevent
overdrive from certain models of exciler-modulator.
This is especially trueforthe 10 watt system, because in our basic transmitter family a 10 watt ampliﬁer is simply
a lightly driven 50 watt ampliﬁer, and a 50 watt ampliﬁer is like-wise a Iightty driven 250 watt output stage running
without its driverIlP/L (Our 250 watt transmitter lineup needs an additional IPA to get enough drive to the
identical ﬁnal stage that is used in the 50 watt and 10 watt lineups).
2. RF Preampliﬁer 10A145365 (Low Band) and 10A145364 (High Band): Figures 2 and 6.
This preampliﬁer design originany appeared in the aural/sound sedion of a dual RF chain transmitter which
operates two single RF chains in quadrature and therefore requires phase and gain control at the input to each
chain. The same unpopulated cirmit board is used for the present application, therefore has the pads and holes
for the components which performed the adjustment of RF gain and phase in the paraliel systems. in a single
chain transmitter such as the present one under discussion. there is no requirementforoontrol oi RF phase nor
mnsequemty its components; they are therefore removed and wire iumpers substituted.
in the Low Band preamp, the 50 0 input cable is matched by C5. which uses the indudance of the traces on
the PC board to form a low pass matching network. and fed to ampliﬁer U2 whose output oonneds through a
table to the PA U2 is a linear ampliﬁer designed originally for use as a wideband cable system trunk ampliﬁer.
Cable ampliﬁers are nominally 75 ohms in and out. but the MHW6185 is capable of a good match with 50 ohm
source and load. 012 and the lead inductance of a CA2885 when used as U2, perform output matching to
50 0. C12 is not present in a board using an MHW6185 for U2. The gain of U2 is spec'd as 18 dB. and
allowing a few dB of losses, the gain ofthe Low Band preamp is 14 lo 16 dB.
RF power FEi's operated in High Band ampliﬁers exhibit about 6 as less gain than they do in Low Band. so an
additional ampliﬁer is necessary to make up the diherence. The High Band preampliﬁer therefore consists of
two stages.
In the High Band preamp. the input Is matched by 05 and the PC trace inductance which togetheri'orms a low
pass matching network and the signal is led to on additional preampliﬁer stage U4, whose output appears as
the inputofuz, which in tum feeds the board «implacable. The speciﬁed gainaftype MWA330 in the U4
pasiﬁonisGdB. andatype MHWG1850rCA2885(U2) is 1BdB. Aledeoflossesexistonthe board, some
effective gain or the High Band preamp board 10A145364 is about 20 to 22 dB.
High Band preamps 1m145361 used in higher powered externally diplexed transnﬁttar aural service. have a
type MWA13D instead of an MWA330 for U4. Speciﬁed gain of an MWA130 is about 12 dB. but we don't
recommend substitun'on of U4 in any internally diplexed system due to overall linearity and inten'nOd
requirements which are mud'l more stringent in the imemally diploxed case. This is because the 30 dB (or
thereabouts) of aural to colour subcanier isolation manually provided by the diplexer is not there. and it simply
means that hternally diplexed system intermod numbers have to be much better.
Atlhe output at U2, a thatch to 50 ﬂ is provided by C12 and the device lead inductance. which together create
a low pass matching network in boards where a type CA2885 cable ampliﬁer is used; conversely a type
MHW6185 device characteristics give it a wideband match to 50 0 therefore no special output matching is
necessary. and 012 is not present
U3 is a voltage regulator providing +24 V to the preampliﬁer sagets).
PUBSM? rev cn Ber; 17. 1993 HQ FA 5 Heatsink Assembly
VHF POWER AMPLIFIER & HEATSlNK ASSEMBLY
3. SRF 3843-2 RF Power Ampllﬂef: Figures 3, 4, 5, 7, 3, and 9.
The Power Ampliﬁer (PA) is conﬁgured in push-pull. using dual N-channel enhancement mode Field Ellecl RF
power transistors whim are packaged into a single case and operated in dass AB.
The Low Band and High Band versuons of the PA differ slightty due to the frequency ranges to be covered.
3.1 Low Band PA Circuit Descriptlon (30C1054 input board, 3001055 output board)
The PA consists of two, source grounded N-channel. insulated gate Field Effect Transistors (Ft-Ts) packaged
in a single use, operating dass AB ‘n a push-mil conﬁguration. The original smematic indicates a type
MRF-15tG as the dual FEI' used; we now use a "selected MRF-151-G to tightly controlled speciﬁcations" whim
is pmprieﬂryto LARCAN and designated type SRF 3943-2. This selection simply tightens the gain speciﬁcation
for operation in High Sand, and in case of emergency. there is no reason an MRF—151-G could not be
substituted for Low Band operation.
Because these FEl's are "enhancement mode N-dtannel“ devices, they require positive gate-tc—scurce bias
voltage on each gate to cause sourcediain conduction. The quiescent Class AB idling bias current is set at
0.6 ampere for each half. The gate voltage required to produce this idling current may vary between 2 V and
5 V according to the device spedﬁceticn sheet. and typically is 3 to 4 V. FET gate threshold voltages also are
temperature sensitive, so thermal compensation is provided by RTl and RT2.
Gate bias is supplied out or adiustable voltage dividers from +20 v regulated bias sources CR1 and CR2.
Current limiting to these zener diodes is provided through R1 and R8. Resistors R9, R2. R3. R4, and RT1
provide gate bias forms "A" half of the ampliﬁer, R10, R7, R6, R5, and RT2 provide bias for the "B" half.
The RF input signal arriving in J1 is applied to balun T1 to provide two signals 180“ out-ot—phase. These
antiphase signals are stepped down to match the low input impedance of the FET ttvough a n-netwont
consisting of C1, CZ, C3, L1, L2, C4, and the device input capacitance. and then applied to the gates. The
GpadtancevalueofCati-dtangedforopeiaticn on channels5s5. The gate inputimpedanceatme operating
frequencyislwloomparedwith thevalues ofst R6, which have IittleornoetlectatRF.
R3 and R6 provide a DC path for bias, and provide loading at lower frequene‘es where gate impedance is high,
in order to assist in maintaining amplifier stability. The choice of 06, C7, C20, and 021 values, their series
inductanms, and that of board traces. also ensures effedlve bypassing at cortical frequencies
The output matching rmotwork. consisting of inductors L3 thru L5. and capacitances C13 thru Clo, transforms
the very low output impedance of the FET, upwards to a standard 50 Q. The two antiphasa output signals are
ﬁnally combined in balm T2. Le Jumpers placed across parts of L7 and LB, plus the changed values of C13.
C14. 015 and C16, conﬁgures the system for channels 5 8- 6 operation.
DC is applied to the FET drains through L3, L4 for the 01A half. and L5, L6 tor the 015 half. L3 and L6 are
short sections of microstrip line which transform the apparent RF impedances of L4 and L5 to higher values as
seen by the FET. RF and lower frequencies are bypassed with paralleled coma. and C17 forthe "A" hailol
the ampliﬁer, and C11, 012, and C18 for the "B" half. These groups of capacitors are selected in value and for
their internal equivalent series inductances so that they will be an eﬂeaive bypass at enlist frequencies of
interest, including video, to assist in maintaining stability. The connections for C2!) and C21 also assist in
sterility due to their return palm through the ground plane of the output board. This connection provides a small
amount of negative feedback as a primitive means of neutralizing the ampliﬁer
The RF output leaves the board from J24
PUBQM M 0: Dec 12 1998 3243 PA 3. Hemmk PBSEMNY
VHF POWER AMPLIFIER & HEATSINK ASSEMBLY
3.2 Low Band PA Setup Procedures
1. Setupa48Vpowersuppty,e.ln'entlimitedtoalittlemoremanlzemps.
2. Remove both fuses on the power ampliﬁer. Tum Dom bias potenliarnehers to their maximum resistance
position ( minimum gate voltage).
3. Apply the 48V supply to the B+ terminaL Verity that the bias (gate) voltage is at Or near minimum by
measuring the dc voltage at the gates of me device. This voltage should be less than IV. Install one
ofmefuses and slawlyadjustme eenespmdlng bias potenﬁmnetarmrsoomminmnnrarefsr
the fuse to the other side and adjusi the corresponding pot for 500 mA of dmin went
4. Connedazade,1Wanenumortamepummofmeampliﬁsrasshownmmediagrambelw.
5. install both! fuses and apply 5+ in both supply connections of me ampliﬁer module.
6. Apply a low level sweep to the ampliﬁer and measure the DC input curent (not more than 1.2 amps)
and gain. Gain pfthe ampliﬁer alone should be about 20 to 23 dB, and with the preamp in circuit the
combined gain show be between 40 and 43 dB. Flamess ever the band should be betterman 1 as.
as shown in the Morning diagram. Curves for an 2-4 and 5,6 are apnea farthe PA alone:
so vnt: ll-SA nurmr
(LAB PMPLV)
._ \.
liIIINLE UNI! YESY
rectum mes:
MDDEL 'M' TX
AMPLIFIER SWEEP
I7“:
van
mun m 047-13
./.m ....... J
Sweep setup and response for PA alone, Without preampliﬁer.
PUBSBJ2 m0: Dec. 12, 1998 32-4 PAS. Heah'nk Milly
VHF POWER AMPUFIER & HEATSINK ASSEMBLY
3.3 High Band PA Circuit Description (208122262 input board, 205122661 output board)
The PA consists of two, souroe grounded N-dhannel, insulated gate Field Effect Transistors (FEi’s) padtaged
in a single use, and operating in a push-pull oonﬁguraﬁon in class AB. A single specially characterized device
designated SRF 3943-2 is used for this High Band ampliﬁers These N-diamel FETs are "enhancement mode“
devices. so require a positive gate4o—soume bias voltage on eadt gate to cause source-drain conduction.
Quiescent Class AB idling bias cunent is set at 0,6 ampere foreach half.
The gate voltage required topmduoethisidiingumem mayvarybetweenzands Vduetoverianoesamong
FETs, and typically is 3 lo 4 V. Gate voltages also are temperature sensitive, so temperature compensation
is provrded by RT‘l and RT2.
Gate bias is supplied out of adjustable voltage dividers from ~20 V regulated bias sources CR1 and CR2,
Current limiting to these zener diodes is provided through R2 and Rat Resistors R9, R1, R3, R4. and RT1
provide gate bias for the ‘A" half of the ampliﬁer; R10, R7, R5. R6, and RT2 provide bias for the "B" halt
The input RF arriving in Jt is applied to balm T1, L1 to provide two signal outputs 150' outot phase. These
signalsarasteppeddovmtomatohthe lowinputlmpedanoeotthede'vicemrough adual section, twinnnetwork
consisting of C1, C2, L2. L3, 03, and the device input capacitance. and then applied to the gates The gate
impedance at the operating frequency is much lower than R3 and R5, so these resistors have Iittie or no sited
at RF.
R3 and R5 provide a DC path for bias. and provide loading at lowerfrequendes in orderto assist in maintaining
ampliﬁer stability The choice or (32 and 08 values, and their internal equivalent series inductanws, also
ensures ettedive bypassing at oritirzl frequencies
The output maid-ling n network consisting ofIndudors L5 thru L10, and oapadtznoes C12 lhm 016, tunes out
the FET drain capacitance and transforms the very low output impedance of the FET, upwards to a standard
50 ohms. The two 180" antiphase dugout signals are ﬁnally combined in balun T2, L11.
DC is applied to the drains through L4, L5 for the "A" hall, and L6, L7 tor the ‘B” half. L5 and L6 are also short
sections of mimostrip transmission line which transform the apparent RF irnpedanoes or L4 and L7 to higher
values seen by the FET. RFand lowerﬁequendiesare bypassedmm C1, 010, C11. and CS, 09, C7.
These groups or capadbrs are seleded in value and for their immal equivalent series inducﬂnoes so that they
will be an effecﬁve bypass at all frequencies of interest induding video. to assist in maintaining stability.
Towards this obiedlve of stability. in addition to resonating with the device drain-tediein capacitance at RF,
Inductor L9 places a heavy load on the FET output at lowtrequendies, where it behaves as a dead short
3.4 High Band PA Set Up Procedures
1A Selupa48Vpowersupply,wl-rentﬁmitedtoe litaamorethantZA
2. Remove both fuses on the ampliﬁer. Tum both bias potentiometers to their maximum resistance
(minimum gate voltage).
3 Apply the 48V supply to the as terminal. Verify that the bias (gate) voltage is at or near minimum by
measuring the voltage at the gates of the device. This voltage should be less than N. Install one of
the fuses adjust one of the poﬁntiometer for 500 mA dram current. Then adjust the other potentiometer
tor a total current of 1A.
PUBSS-ZH rev 0: Dec. 12 1996 325 FA Kt Heasink Assembly
VHF POWER AMPLIFIER 5 HEATSINK ASSEMBLY
3.4 High Band PA set Up Pmeedum (continued).
4. Connect a 20 dB 1W anenuatorro lhe output of the ampliﬁer as shown below.
5. Apply 8+ a: born supply connections of me ampliﬁer.
6. Apply a low level sweep lo the module and measure the DC input current (spam 1.2 amps) and gain.
Ampiﬁergain by Mshould be 15 lo 17 dB, and with preamp included. were! gain should be between
38 and 41 dB. Sweep response should be flat wilhin 1 dB over the band as shown in the sweep
diagram fmm page 4, repeated below. Note ma! these sweep wrves are applicable lo the push-pal
FET ampliﬁer only and (he preamp is not induced.
MEP usclLLArm
50 um: ﬂ-SA mrrwr
run P/squn
TF mlrlzi mmz'
MIME anti res!
mum Em
MDDEL ’M’ TX
AMPLIFIER SWEEP
u-m .
Sweep serup and response for PA alone. win-lam preampliﬁer.
Fuses-32mm: Dec. 111995 32-6 PA5HatsmkAssembly
LOW POWER VHF AMPUFIER CONTROL & METERING PANEL
Contents:
Sec Topic
1 Controls. Metering Panel Desaiption ..........
2 Ampliﬁer Control Cirmll Board Desu'ipﬁon .......
List of Flguns:
Hg Title Drawing Reference
1 Ampliﬁer Control Board Assembly ...... r . . 3601829 sht 8
2 Ampliﬁer Control Board Schematic A , ........ 2032438
1. Control Panel:
Ampliﬁer control arid monitoring is performed by the Control and Metering Panel. This 19“ wide, 3 unit (5' 1')
panel serves primarily as a mementos] mounting for the amplifier: contml witches. status indhemr lights. and
a multifunction meter. The panel is the mounting for the coml circuit board described below. and elsewhere
on the dtassls is an output metering circuit board whid’t is described later in this manual.
The Ampﬁﬁer control panel features as seen from the front, are these:
1. 50 uA panel meter ﬁtted with a power scale wlibreted 0-125 pereent
2. The meter input selector switch for farward and reneded power.
at Pushbuttons for ON Sr OFF;
4. Three LEDs providing initiations (from lett to right) man lighted: EXT 1 interlock is dosedﬁhe outwl
ampliﬁer TEMP lhemtostat is cool, EXT 2 imedock is closed,
The ampliﬁer is provided with a VSWR tailback fundion that reduces its power output to save it from harm in
the event of very high reﬂected power such as an open drmit condition.
The VSWR mew feature is described in the Metering board section at this manual,
Pueessemt Dean isse 33-1 mmmmsez
LOW POWER VHF AMFUFIER CONTROL l- METERING PANEL
2. Ampliﬁer Control Circuit board Assembly 30C182962: Figures 1 and 2.
There are seven connectors on the Control circuit board. These connectors perform the following functions:
J2 connects elsewhere in the ampliﬁer, such as the thermal snitch, relay. and to the 50 pA meter.
J3 connects to the enema! imertodts.
J4 intercenneds with J3 ofthe Metering board.
The transmitter interim chain begins with the +12V at K1-7. When K1 is set ON by energizing its coil K1-1,
contacts 7 and 12 close and contacts 7 and 10 open, turning of! the LED inside the OFF button S4. The +12V
tom dosed contact 7-12 lighm the LED inside the ON button 53 and ﬁghts the optodiode in U3D, which provides
a logical aﬁive law out of its pin 10 for a remote control status interface. This status signal simply tells the
remote control through J5-6 that the transmitter was instructed to be ON, nothing more.
The +12Vtrorn comer: 7-12 also comes out of the board on J35, which is one side of the EXT 1 interlock EXT
1 in targertransmitters is often used with a ﬁre alarm system to stop all blowers, and in lower power transmitters
it is still worthwhile that a nonnalty dosed ﬁre alarm contact be connected to EXT 1 bemuse the fan(s) in the
transmitter ewld cause enough air currents in the transmitter room to fan the ﬂames.
When the EXT 1 intemok is closed and the +12V appears on J3-4. the +12V is new at DSS (marked m1)
and the optodiode of USC which both light up to say EXT 1 is dosed. The active low from U3C pin 11 informs
the remote control via J5-14 that EXT 1 interlock is dosed.
The +12V now is applied to J2-8 which connects to a normally closed oontaa in a thennustat that responds to
the temperature of the RF power ampliﬁer‘ It a owing fan should stop and the ampliﬁer should overheat, this
contact vvﬂl open and prevent the +12V from appearing at J2~3. This of course breaks the chain and removes
the 12mem the solenoid of the power supply oontador.
Assuming the thennostat is cool, D54 and the optodiode in USE! are lighted, conﬁrming TEMP is okay. The
logical active low out of use pin 14 informs the remote control ofthis fact through J5-7.
Assuming the thermostat is closed, the t12V next appears at J3»3. which is EXT 2 interlude This is the plea
where RF pawl panel link contacts or coaxial switd’t auxiliary eentads. and/or dummy toad thermostat oonlam
would be connected so that the transmitter can only be ON when valid RF paths are present, consequentty the
EXT 2 path from J3-3 to J3—7 will be intali
Fuses-33 M40: Dean 1998 33-2 Commlanrd 30am
LOW POWER VHF AMPUFlER CONTROL 8. METERING PANEL
1 Ampliﬁer Control Circuit board Assembly 3061829G2: Flgs 1 and 2. (conﬁrmed).
Finally. when the interlock chain is complete. the +12V is applied to the solenoid cf the power supply primary
contactar through J2-10, and the cooling tans and power supply are all turned on. The 053 LED marked EXT
in the Metering Board, but the initial threshold setting is done in the pin attenuator board, potentiometer R5.
These simply provide an adjustable reference bias voltage to the AGC m‘rcuit whim adjusts the power output
inversely according to this bias voltage.
in the event of a VSWR that exceeds a preset amount, the AGC voltage becomes modiﬁed 3 little to reduce
the ampliﬁer output by an amount proportional to the reﬂected signal. This "VSWR Cutback" permits the
ampliﬁer to remain on the air at reduced power if the antenna should gradually acmmulats a layer ofice.
The AGO voltage and modiﬁcations to it from VSWR. are summed in U2A which is basimlty a buffer ampliﬁer
that also provides a telemetry output to the remote control system through J5-3.
Forward and Reflected meter intimation is done with potentiometers on the Metering Board.
A 50 uA meter mechanism that is ﬁtted with a scale 042556, is connected to J2-9 and J2-7. The r terminal
of the meter connects to JZ-S.
Although F1 is drawn in ﬁgure 2 as a fuse, in reality it looks like any ordinary disc ceramic capacitor, but It is
a current limiting device similar to a thermistor having an extreme positive temperature coefﬁcient. In nomrel
operation it maintains a low resistance, until it gets not from no mud] lament and then suddenly switd-tes to
a high resistance state so that the current it is able to pass is only a very small amount. This small amount or
current is sufﬁcient to keep it wenn enough that it remains in its high resistance state. When the power is
removed and the device cools down, it resets itself to its low resistance state.
HESS-33 rev (2 Dec, 22. 1998 334! Control Board “15862

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