Harris GATES FM-3H User manual

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FM HARMONICS IN THE TV BAND
The sharp upsurge in FM broadcasting has in some instances developed
unlooked for interference with local TV reception. In every instance this
interference is in so-called fringe areas for TV reception and where the
strength of the TV signal is weak enough that outside highly directional home
TV antennas are necessary. --- When this condition develops, the TV viewer
quickly learns from his service man that the local FM station is the offender.
---- The FM broadcaster is immediately deluged with requests to eliminate
the interference. In some instances CATV (Community Antenna Television)
systems are also offended as they pick up weak distant TV stations. ------
What is the FM broadcaster’s responsibility? Answer: To meet FCC rules
and regulations as related to harmonic radiation of his FM equipment but not
to guarantee perfect TV reception.
Below is a chart showing the picture and sound frequencies of TV stations
between Channels 7-13 inclusive. Channels Z-6 are not shown. FM harmonics
do not fall in these Channels. In fact, commercial FM station harmonics will
affect only Channels 8 and above --- look at the chart.
TV Channel Picture Frequency Band ---MC-- Sound Frequency
7 175.25 to 179.50 197.75
9”
10
181.25 to 185.50 185i75
187.25 to 191.50 191.75
193.25 to 197.50 197.75
11 199.25 to 203.50 203.75
12 205.25 to 209.50 209.75
13 ,211.25 to 215.50 215.75
The frequency range for commercial FM broadcasting is 92.1 MC to 107.9 MC:
--- To determine the second harmonic of your FM frequency, just multiply your
frequency by 2. Example: If your frequency is 99.9 MC, multiplied by 2 would
make a second harmonic of 199.8 MC. By consulting the above chart, you will
note the second harmonic falls in the picture portion of the TV Channel 11.
Correct FM Harmonic Radiation
The FCC stipulates that transmitters of 3000 watts power and over must have
a harmonic attenuation of 80 db. For 1000 watts, 73 db., and for 250 watts,
66.9 db. All reputable manufacturers design their FM transmitters to meet
or exceed these specifications.
Fringe Area TV Strength Versus FM Harmonics
Let’s take a typical FM station that radiates 70,000 microvolts per meter at
1 mile. At 80 db. harmonic attenuation (as called for by FCC), this station will
radiate approximately 7 microvolts per meter at 1 mile on the second harmonic.
In the case of our Channel 11 example, it is estimated that a fringe area TV
station from 60 to 90 miles distance would have a signal strength of from 5 to
25 microvolts per meter. It can then be easily understood that a 7 microvolt
signal, well within FCC specifications, would definitely interfere with the TV
signal, yet with the FM broadcaster’s equipment performing normally.

This is sometimes further aggravated by the FM station being located between
the TV station and the TV receivers. In this instance the TV antennas are
foixssed not only on the TV station but your FM station as well. The home
TV antennas are beamedat your legal second harmonic as well as the fringe
TV station.
What To Do
When interference occurs, it will develop ragged horizontal lines on the TV
picture varying with the FM program content. If the TV sound portion is
interfered with (usually not the case), then the FM signal will be heard in
addition to the TV sound.
1. It is not up to the FM broadcaster to go on the defensive. He did not put
the TV station 75 miles away nor did he select the TV Channel. ---- In
most instances the condition is a natural phenomena that neither you, the
TV station, nor the FCC can correct.
2. Do not adjust the FM harmonic or “T” notch filters supplied with the
FM transmitter. These are factory adjusted and most FM stations do not
have the expensive equipment necessary for correct adjustment. Tampering
with this calibrated adjustment will probably make the condition worse.
3. Do not rely on TV service men’s types of measuring equipment. They are
not built to accurately measure harmonics and invariably give erroneous
readings that invite the CATV or local service men’s association to say
“I told you so.‘.’ Remember it is difficult to radiate harmonics if the
equipment is built to suppress the harmonics and it is.
4. In many instances interference may be caused by overloading on the front
end of the TV receiver. This problem usually occurs when the receiver is
located close to the FM transmitter. This problem can be overcome by
installing a trap tuned to the frequency of the FM carrier. The TV service
man can and must learn how to do this. In most cases it works, while in
some instances, if not properly installed or tuned, it will not completely
eliminate the interference. In one case where interference of this type
existed, a TV station put traps for the fundamental FM frequency on
nearly every TV set in town. Not the FM transmitter.
summary
The FCC is well acquainted with this nation-wide problem. If TV viewers write
FCC, complaining about your FM station, remember the FCC has received a few
thousand similar letters. --- It is not the obligation of the FM broadcaster to
assure fringe area reception of a TV station any more than is the obligation of
the TV station to assure the FM broadcaster perfect reception in his TV city.
Probably your installation will not have problems as outlined above. If they do
exist, don’t blame the equipment. Every transmitting device puts out a second
harmonic, even the TV stations. The fact that these harmonics legally fall into
the spectrum of a TV station many miles distant is coincidental, but not your
fault.
Gates Radio Company

%.I
I.2
12
1.2
1.3

SECTIO1? 1’ - GENERAL DESCRIPTIOI~
1.1 Warranty and Safety Notice
This equipment is guaranteed under the lib&l Gates
Warranty, tezms and conditions of which are fully set
forth. in the standard Gates Wa’arranty, availab1.e upon
request.
Most Gates manufactured items axe guaranteed. for one year,
M.th the exception of tubes and moving pa.rts,. which are
subject to. specific warranties based. upon hours of usage.
The Warranty does not extend to 910 chargerz service on
the fieMc
Switch to Safety - This equipment employs voltages which
are dangerous and may psove fatal. if contacted by operating
personnel, Extreme caution shoulM be exercised when working
with the equ.%pmenti. Observe safety regubstions. no not
change tubes OX=make adjustments inside equipment with
eny
voltages on,
WX.le your Gates transmitte:e is ful1.y irks:?-
looked you should not rel-y on the interlock switches fo?
removing high opera.tin,g voltages. It
ia always best to d.is--
OOu,.I?RCt
the psimary po;‘;er a,t the building wa3.1. switch and
discharge a,lJ capacitors wi th the grouzding s-k..~% providet?,
le2 Purpose of Book
This irmtruction book has been prepared to assist ia the
instal.lation, operation, and maintenance of the Gates FM--31ip
3 Kw9 ml transmit-ter,
1.3 Purpose of Equipment
Th.e Gates FN-3H j & an FM bs?oadcast tr-ansmi.ttcr with 3, OK?
watts output delivered. to the transmission Iii nc o The aper-
sting frequency i.s 88-1.08 HR:: with characteristics exceeding
those required by the B?dcraI Communicati,ons Cornmissior* for
standard FM broadcast sr:rvico. The transmitter is designed
for continuous b:?oadc;ast ope:ration a,& consists of tb.e exciter,
intermediate power ampLi.fi.er, and. the power amplifier, plus
thei x .associa%ed powei.~ suppl,.ias.
I..4 Gescripti,cm
0nl.y one cabin& is rcqu:Lrc:d to home th,e ontire transmitter.
ThiS cabinet is 42rr wide x 7Srt h.i& x 32 3/L&” deep* 81.1 neC(:s-
sary metering is uzovided. JY:Tfour msters loss,toc? on a metes
panel. at the top of the ca:>inet, Re.3d.y access to the co:np:Ce-te
t~a~lSi~l:i-t;t~~ iR .%CCO~npI:i.S:h~d h3
J re<!rovaHe ~‘ear d.oor, hSngec?
access panel., and hinied cover 0.f t!rc exciter unit B &?o1;r.i:
dOOj:s
are .provi.docl to offer a piea;ii.ng and symmetrical f?cr,%

1.6 Vacuum Tube Table
The following tubes are employed in the transmittex,
Symbol Designation Tube Type Function
v2
V’I
Mx250E
4CX5001)h
Intermediate Povfer
A3liplifiW2
Power Amplifier
The FM-3H is carefully rjackea at the Gates plant to ensux%
safe arrival at its destination, The equipment is packed i.n
a number of heaiiy cartons and wooden crates, 0;Zen the crates
and cartons carefully to avoid damaging any of the contents,
Remove the packing ma,teria.l and search for possible small items
such as pilot lights, fuses, loose screws and bolts.
1% dkmage should occur during shipment, a4.3. claims shouLd~ be
filed promptly with the transportation company. Xf 8 ciaim
is to be fil.ed, the ox!,gim,l packing oase and matcr+.al must
be preserved., A damago report must be filed to c013,,ec? fozL
shigpinp de.mages, Gates Rdi.0 Company is not responsible lo2
damage occurring during shipment e Parts or components shApyed
to replace those damaged in transportation will be billed to
the customes plus transportation expenses, the cost of wh5ch
should form a portion of yous claim to the txanspoPfafion
company *
A complete via;zaL inspeatiou should be made of the 3q&++21t
lhtermiae that there are YIO loose conzections, loose ~omyon-
entsp broken insulatore, eke,, t&t r?.ay have bees damaged in
shipment 0 Pbke sure all relay oontacts am free and in good
meohanioal conditions Make sure a13 mechanidal. connectdons
ax-c tight* Check with a screw dr~ivsr or a wrench, all. me&an-
ioal and el.ectri0a.l conneOt7ion~ that arc mechanically bOlfe8
-together, All. tic downa 022 bl_OCM.E~ Esed for shtpljin:: p.??pO.5~~
shQuld. be reinoveli, A good o-~csal.1 vbsuril
inspeation isay save
time and trouble i.n placing the trensnitte~ into operai.irig
condition,
2,2 Packlng Check List
Certain comp0aen.t~ of the tran.smitteer have been removed fop
shipment and arc packed scpavxtel.y to ensu.~e safe ha~nd!.in,g-.
These parts on the QI’&3H ha,ve been kept to a bare ninlmuin
and are plcg-in units and ?lc;?xy 00mp0;1en;:s, I’ubea that are
not cXampeG down for no~.zK!! operation ase a!.so ~nar::,ovca:,
The fol.l,ovfir,g compomei2ts have been removed from the trans-
mitter for shipping purposes:

:. .
Remount the two monitor coupling
balun,
loops on the exterior Yertica~-
The lower end of the inner-conductor of the balun connects to
output loading capacitor C6,
Loosen the Allen set screws on the adjustable portion of the
balun. The distance that this component is positioned vest%
tally f?om the tube deck varies with opemtin.g frequency.
Refer to your test data sheets for the prGper measurement on
yous asoigned cha.nnel. This
l/8” for proper operation. adjustment must be accurate rii.thin
The 4CX250B, ceramic chimney, and exhaust tubing axe installed
in the driver cubicle, Rig~o 7,4* Place .the tu.be in ite
socket D s11.p on the ceramic chimney, and clamp on the anode
connector, Drop the exhaust tube through the opening of the
upper tube deck to the top of” the 4CX250B, Hold the exhaust
tube in place with 0 rings above and below the deck nurface,
InstaSSing the 4CX5OOOA is slnpSe.
cov~ered in Section 2-4. Ms.ndSi.ng of thi.s tube is The anode colln.ec!tor assembly E;ecures
with a cl.amp to the tube and with a bolt to the plate line&
Coaxse frequency tunin~g 07 the piate circuit is determined by
the distance of the rotary portion of the pl,.ace circuit from
the WX’iOOOA tube deck. This measurement is recorded in. the
test data for your tsnns!a~.t-ter a,nd shou1.d be checked befoz
ope!rating the transmitter,
k/16 " a
Tolerance here is approx5mntel.y
BGlt the IOW pass filter in the transmission Sine bet;:reca the
kixectional coupler and antenna coa,xg
eion is compIete, and your basic inctalJ.a-
The wet&t of the low pass
fi.S-ter Ghma~"d n?st
be applied to the l-5/8” coaxial.. components directly. p;yOV-je-~.
srons shoul.cl be mado a,t the transmitter site to ha.ve at Icast
twG supports for the filter,
2.4 Tu.be RandLing and. Operating Precautions, YCFjCOOA
Avoid bumping thin tube0 Due to Its Large mass, bump:ing tM.s
tube will. introduce res~~l.tani: stresses
damsg;e E which may muse Internal,

area than the apening a-t the top or” the transmi?itcr~ Shrp,
right-angle bends are not permissible.
to turn a right-angJ.e$ These it is necessary
a radius t ape bend should be used,
There are na.ny installation nosn%bilUties,
installation is somewhat dif?erent E E2Ch Eilad KVC~jr
Therefore, it is Rot
possib1.e to give complete dei;aiZLed informatiora. on the ‘cran.+
mitten ductin.g.
As a suggestion, Only genezeal. information ~2% be supplied.
contact a looal heatirg alid cooii.ng con-
tractor for a detailSed analysis of the probl.em.
S%X!ION 3 -* OPXRATTOW
3.1 Pro-Oparation
If everything appears to be in o.rdor’, -than you nny prclccca~
3-2 Text Ilata

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for the maximu outp-ut and the most 0veral.l efficient cendi-
The muitimeter switch (SIO) located on the meter panel. will
give an iildicatio i"l of the amo;rr,t of drive to the grid of the
PA -tube, This is a relative indication and is read with the

This transmittes is a precision. electrical device, and as such9
should be kept clean at all times a@ free of dust and fow3.g~
material, Dust and moisture con,densation will Icad ‘GO possible
arc avers and sh.ort conductive ca’c?o.s,
A good preventive maintenance schedule is always the beet assur-
ante for trouble free transmitter operation, _
SECTION 4 - CIRCUIT DESCRWTION
The l?&=3B circuits will be desayibed in the foliowing secti.ons:
Power AmplifSer Pay32 Supply
.intermediatc Power
Amplifier (PA) CoMxol Circuits
Exciter MeteTir3g
See %IILIStY~tiOi~ 7.7*

The intermediate power s.mpkifier employs a 4CX250B tetrod.c ii:
a common cathode circuit. The grid circuit. is capacity tuz~ed~
The plate .circuit is common M.th the PA grid as previousig
explained, screen bypassing is e.ffectgd with the ~bullt-in
bypass of the 4CX250B air system socket. The IPA cathodt? is
bypassed with four ceramic button. capacitors.
4*3 Exciter
The Pi% exciter is described in dctail in the exciter instruc-
tion book.
4,4 Power Supply
Only one high voltage powor supply is nsed in %he R&5::, It
supplies 4-5 KV for the PA pkte and 2 KV for the PA ecz+*e?v.
v01tElg-e f and the IPA plate, The basic confi,gura~~iou c;:f the
supply is a three phase fuU wew bridge.
2 R’S is obta:..hod
from-the center tap of the transformer to supply the IPA pleto
and also supply the sou~‘ce for the variable voltage of betweer~
300 V. and 1500 V. for th,e PA screen grid, Series Ihmitin~
resistor9 H-47, prevents the PA screen grid from over-dissi~l~~tti~g
in cast the PA has a 103s of plate voltag*:.
The 0 to 270 irGlt vari.ab1.e :iu.ppl.y for the I!:.:. $,CjyE:en voj.tl;~c~
is also denivcd from the 2 KY centor tsp soli~~e. IQ(; 5-3 ‘I;k$>
contsol. c.
The rectifiers for the suppl.y 21-a mol.dc:d si.1ic0r. col”l.mns
n;ounted on. 2 panel. attzched to the
sj. d0 0f t be trsn~r3~i t-l; er +
The six co!,un;~s are wire. d to form. a t1wee ph ase ~r]u‘iJ~~.er c!i~xTai,t 0
The PA bi.as sv.pp!.y is a sing1.e phase ftY.3. W~YC?b:~!.dgc; circuit
using ailicon rec’tifiern D Grid. bi,aa
bc~~\*f~en yyl .to 1.75 ?,rOli;Q
is supplied to the PA control grid. The bleeder re<sis-toj!
across the supply, R-41., wi.3.1 al30 provide additj.onsl bias
voltage if the PA grid current duo to i?P d-rive causes gri.d
current to flow
rrhout 40 m witA I60 volts fixed bias (, n
is the bias ad,just control..
4-e5 CO??,t.1..0!. C!i:‘i;&tS
The con-trol circuits of the T~--:j~i consist of the fo.,l.Ic;i.:ir.!g:
- I<1 Primary Coatac’cor - aippliea voltage to the filaments,
fXCj..%el?, and energizes the blower.
- K2 r1.2te Cont2ctos -. z,P~l.ic:: pri!:23.:t’y voLta.ge to the
plate ‘tr?wls.for!Ilr:r (x.2 is
r;norgizer: after K3 oloe;-.liu )
.-J-Z... p;q- 31~1

The sixand meter r&ads PA plete current and is Located in the
Plate Ed=iecd, The meter is properly insulated and I.so%atecl
behind a protective plexiglass cover.
The third meter reads plate, valtage aud is loos-ted on the Itiw
potential. side of the meter multiplLi.er resistor,
The fourth meter is for indicating power output a.nd YSviR 011
the transmission li.ne. This meter works irl conJunction with
the directional coupler mou::ted irL the oiitput transmission
line,

5.3
Pi%31-I PAWS LIST
-01 No.
Al. Neon Lamp .25 I? (part of? Sh)
A2 Neon Lkuxp
.25 W (part of S5)
Bl
B2
Cl- $C35
G2,C3
C6
c7
C8 thru Cl.6
cl8 tkru c23
C42
C45,W6
CR],.
CR2,C.26
cx3,CR4,CR7
CR5
DC1
PI ,F2 398 0182 000
F3,W.,I?5
398 033.9 000
F6 398
0213 000
F7 398
0017 000
PLI. 992 3.600 001.
FL’
942 3920 ox
J1
J2,J3
J4
Ga'ces Part No. De&&ion
--. ---.
432 0010 000
436 0013 000
516 0043 000
Blo;-ler, L/3 B,P. 3500 XPIT,
U.5/230 V.
Motor) I. Pi?, Ratio 3211)--L, IL0 VA
cap., 470 pf,,
1 KV, Ceramic d..i.sc
Can. L *oc3~ uf.. 1 KV. Ceramic dike
_
516 0054 000
914 1912 001 Var. Cap., 6-12 pf. (modif.)
516 0233 000 HV Cap.., 500 pf*, 30 KV, ceramic
516 0205 000 WV Cap., 500 pf,, 5 KV, ceramic
516 0206 000
522 0071. 000
516 0227 000
520 0228 COO
516 0250 000
520 0158 000
516 0054 000
522 ol.33 000
516 0082 000
516 0200 ‘000
524 001.7, 000
510 053.0 000
516 0389 000
516 0233 000
516 0210 000
394 0006 000
386 0016 000
384 0020 000
384 oly4 000
927 3270 003
612 0230 000
613 0237 000
612 0,733 000
570 0120 COO
570 0l.s.y 000
574 ooqy 3QO
Cap., $x500 ;.fn 10 IX.
Cap,,
500 pf , ) jo FL,
Cap.,
200 pf,, 7.5 KVa

Symbol No. Gates Pa.rt No.
574 0054 000
572 0125 000
572 0066 000
572 GO52 GO0
913 8288 001
542 3910 001
826 9569 001
494 0004 000
913 9335 cm1
913 9343 cc\1
913 9346 001
813 9379 001
813 9380 001
476 0014 000
476 0186 000
4j6 0035 000
632 0547 002
632 cm0 co2
3? 0545 m
635 0582 002
RZ.,R2,!~3,R4 540 0594 000
a5 9Nl'l !yK> 0058 000
B6,X3tJR13rR%5 550 0067 000
R7 54-o 0070 000
R8 550 COP.9 000
R7.0
Rll,R28,R5L
Rl2
x14
Xl5
Rlii
542 0204 000
550 OOGIL000
$to 0580 000
540 0746 000
540 0068 000
540 0073 000
550 0054 030
,542 OL64 000
552 000
542
0807
oogj000
550 0055 000
542 0058 000
54.2 01.66 000
552 0324 000
540 0573 000
542 0218 000
542 0224 000
552 04.23 000

Symbol. No. Gates Part No,
R47
R4% 542 0370 000
9x3 3424 001
R49,R50 542 0312 000
R52 540 0628 000
R53 540 0305. 000
R609R61,R62 542 0090 000
R63,R64 542 0309 000
R65 542 0327 000
Sl
S2,S%
ho0 Oi6i 000
604 obg6 000
604 0284 000
604 0283 000
6OLi.028G 000
Description
VI 374 0016 000
v2 374 0081 000
404 oo:.c,000
XC42
IXPIy
2 ps 6) 402 0015 000
Xl?:,;
4 ?c5 ) 402 0037 000
XF7 402 0021 000
XVI. 404
xv2 404
604 0285 000
604 0032 000
604 025% 000
602 0055 000
602 0056 000
604 0052 000
472 0409 000
4+2 0090 000
472 020% 000
472 0535 000
6:L4 0059 000
614 0071. 000
614 0052 000
614 0114 000
G3.4 03.04 000
-I.?-

i.
ADDEKDUPlTO INSTRUCTION BOOK888 0924 001
,I M6425 TE-1 FM EXCITER
Gates Radio Company is supplying a 3 dB isolation pad, AT1
(992-2241-001) with the TE-1 FM Exciter. This should be
installe~d between the RF output of the exciter and the input
of following amplifier stages.
The TE-I exciter is capable of supplying RF drive in excess
of the amount needed for most transmitters. The pad provides
additional isolation md de-coupling between the excgter and
following amplifier stages.
When the TE-1 exciter is supplied in a Gates transmitter, the
pad is already installed. If the exciter is supplied alone,
the pad can be installed at any convenient point in the trans-
mission line between the exciter output and following amplifier
stage. Coaxial RF fittings are mounted on the pad for ease of
installation.
PARTS.LIST
AT1 Isolation Pad, 3 dB -- 992-2241 001
gymbol No. Gates Stock No. Dekription
612 0233 000 Receptacle, Type "N"
612 0237 000 Receptacle, Type "BNC"
R35, R36 540 0598 000 Res., 300 ohm, 2 w.
R37,R38,
.R39, R40 540 0584 000 Res., 75 ohm, 2 w.
B/24/67 Gates Radio Company
Quincy, Illinois