Harris GATES M-6573 User manual

mImanatmI
N-6573
FM-1H 1KW FM TRANSMITTER
HARRIS
INTERTYPE
CORPORATION
a A TES!

WARRANTY
Seller warrants new equipment manufactured by Gates Radio Company against defects in material or work-
manship at the time for delivery thereof, that develop under normal use within a period of one year (6 months
on moving parts) from the date of shipment, of which Purchaser gives Seller prompt written notice. Other
manufacturers' equipment, if any, including electron tubes, and towers shall carry only such manufacturers'
standard warranty.
Seller's sole responsbility for any breach of the foregoing provision of this contract, with respect to any
equipment or parts not conforming to the warranty or the description herein contained, is at its option, (a) to
repair or replace such equipment or parts upon the return thereof f.o.b. Seller's factory within the period
aforesaid, or (b) to accept the return thereof f.o.b. Purchaser's point of installation, whereupon Seller shall
either (1) issue a credit to Purchaser's account hereunder in an amount equal to an equitable portion of the
total contract price, without interest, or (2) if the total contract price has been paid, refund to Purchaser an
equitable portion thereof, without interest.
If the Equipment is described as used, it is sold as is and where is. If the contract covers equipment not
owned by Seller at this date it is sold subject to Seller's acquisition of possession and title.
Seller assumes no responsibility for design characteristics of special equipment manufactured to specifications
supplied by or on behalf of Purchaser.
Seller shall not be liable for any expense whether for repairs, replacements, material, service or otherwise,
incurred by Purchaser or modifications made by Purchaser to the Equipment without prior written consent
of Seller.
EXCEPT AS SET FORTH HEREIN, AND EXCEPT AS TO TITLE, THERE ARE NO WARRANTIES, OR
ANY AFFIRMATIONS OF FACT OR PROMISES BY SELLER, WITH REFERENCE TO THE EQUIPMENT,
OR TO MERCHANTABILITY, INFRINGEMENT, OR OTHERWISE, WHICH EXTEND BEYOND THE DE-
SCRIPTION OF THE EQUIPMENT ON THE FACE HEREOF.
RETURNS AND EXCHANGES
Do not return any merchandise without our written approval and Return Authorization. We will provide
special shipping instructions and a code number that will assure proper handling and prompt issuance of
credit. Please furnish complete details as to circumstances and reasons when requesting return of mer-
chandise. Custom built equipment or merchandise specially ordered for you is not returnable. Where return
is at the request of, or for the convenience of the customer, a restocking fee of 15% will be charged. All
returned merchandise must be sent freight prepaid and properly insured by the customer. When writing to
Gates Radio Company about your order, it will be helpful if you specify the Gates Factory Order Number
or Invoice Number.
WARRANTY ADJUSTMENTS
I;
In the event of equipment failure during the warranty period, replacement or repair parts may be provided
in accordance with the provisions of the Gates Warranty. In most cases you will be required to return the
defective merchandise or part to Gates f.o.b. Quincy, Illinois for replacement or repair. Cost of repair
parts or replacement merchandise will be billed to your account at the time of shipment and compensating
credit will be issued to offset the charge when the defective items are returned.
MODIFICATIONS
Gates reserves the right to modiry the design and specifications of the equipment shown in this catalog
without notice or to withdraw any item from sale provided, however, that any modifications shall not ad-
versely affect the performance of the equipment so modified.
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INSTRUCTIONS FOR INSTALLING
AND OPERATION OF
GATES FM-1H, 1 KW TRANSMITTER
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I B - 888 0960 001 GATES RADIO COMPANY
QUINCY, ILLINOIS
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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 2-6 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
8 181.25 to 185.50
9 187.25 to 191.50
10 193.25 to 197.50
11 199.25 to 203.50
12 205.25 to 209.50
13 211.25 to 215.50
197.75
185.75
191.75
197.75
203.75
209.75
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
focussed not only on the TV station but yoür FM station as well. The home
TV antennas are beamed at 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
e ri 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
r an can and must learn how to do this. In most cases it works, while in
,me 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 statirsn 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.
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Gates Radio Company

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FM-1 .H 1 KW FM TRANSMITTER
TABLE OF CONTENTS
SECTION 1 - GENERAL DESCRIPTION PAGE
1.1 Warranty and Safety Notice 1
1.2 Purpose of Book 1
1.3 Purpose of Equipment 1
1.4 Description 2
1.5 Technical Data 2
1.6 Vacuum Tube Table 3
SECTION 2 - INSTALLATION
2.1 Inspection 3
2.2 Packing Check List 4
2.3 Installation 4
2.4 Handling the 4CX1000A 5
2.5 Power Connection 5
2.6 Cooling 6
SECTION 3 - OPERATION
3.1 Pre-Operation 7
3.2 Test Data 7
3.3 Adjustment 7
3.4 Maintenance 9
SECTION 4 - CIRCUIT DESCRIPTION
4.1 Power Amplifier 10
4.2 Exciter 11
4.3 Power Supply 11
4.4 Control Circuits 11
4.5 Metering 12
SECTION 5 - ADDITIONAL INFORMATION
5.1 Remote Control 12
5.2 Stereophonic Operation 13
5.3 Spare Oven and Crystal 13
5.4 Complete Tune-Up Procedure 14
5.5 FM-1H Parts List 1-4
SECTION 6 - M-6425 FM EXCITER
FM-1H

TABLE OF CONTENTS
DRAWINGS - FM-1H Transmitter
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Installation Outline
Low Pass Filter
2nd Harmonic Filter
Block Diagram
Simplified Schematic
Efficiency Curve
Curve - Coarse Tuning
Overall Schematic
PHOTOGRAPHS - Transmitter
Front View (Open)
Back View (Open)
Control Panel (Front)
Control Panel (Rear)
PA Chamber
Base
Figure 7.10
Figure 7.11
Figure 7.12
Figure 7.13
Figure 7.14
Figure 7.15
Figure 7.16
Figure 7.17
Helpful General Information--A thru E
FM-1H

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SECTION 1
GENER&L DESCRIPTION
1.1 Warranty and Safety Notice.
This equipment is guaranteed under the liberal Gates
warranty, terms and conditions of which are fully set
forth in the standard Gates warranty, available upon
request.
Most Gates manufactured items are guaranteed for one
year, with the exception of tubes and moving parts,
which are subject to specific warranties based upon
hours of usage. The warranty does not extend to "no
charge" service in the field.
Switch to Safety -
This equipment employs voltages which are dangerous and
may prove fatal if contacted by operating personnel.
Extreme caution should be exercised when working with
the equipment. Observe safety regulations. Do not
change tubes or make adjustments inside equipment with
any voltages ON. While your Gates transmitter is fully
interlocked, you should not rely on the interlock switch
for removing high operating voltages. It is always best
to disconnect the primary power at the building wall
switch and discharge all capacitors with the grounding
stick provided.
1.2 Purpose of Book -
This instruction book has been prepared to assist in
the installation, operation and maintenance of the
Gates FM-1H, 1 KW FM transmitter.
1.3 Purpose of Equipment -
The Gates FM-1H is an FM broadcast transmitter with
1,000 watts output delivered to the transmission line.
The operating frequency is 8S-108 mHz. with character-
istics exceeding those required by the FCC for standard
FM broadcast service. The transmitter is designed for
continuous broadcast operation and consists of the
exciter and power amplifier, plus associated power
supplies.
-1- FM-1H

1.4 Description -
Only one cabinet is required to house the entire transmitter.
This cabinet is 29" wide x 78" high x 33" deep. All necessary
metering is provided by four meters located on a meter panel
at the top of the cabinet. Ready access to the complete trans-
mitter is accomplished by the removable rear door. The front
door is provided to offer a pleasing and symmetrical front
view appearance. The following controls are located on the
front panel.
a) Filament ON
h) Filament OFF
c) Plate ON
d) Plate OFF
e) Filament Voltage Adjust
f) Screen Raise/Lower Voltage Adjust
g) Bias Voltage Adjust
h) VSWR Calibrate
i) Power Calibrate
j) Power/VSWR Selector
1) Remote/Local Switch
) Grid Tuning Control
m) Plate Tuning Control
n) Output Loading Control
o) (4) Potentiometers for adjustment of PA Plate
Current Remote Reading, Recycle Adjustment,
PA Overload, PA Plate Voltage Remote Reading
p) Neutralizing Adjust
1.5 FM-1H Technical Data -
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Power Output:
Frequency Range:
RF Output Impedance:
Output Termination:
Frequency Stability:
Harmonic Attenuation:
Modulation Capability:
Audio Input Impedance:
Audio Input Level:
Audio Freq. Response:
Audio Distortion:
FM Noise Level:
AM Noise Level:
Power Source:
.5 to 1 kW.
88 to 108 mHz
50 ohms.
Standard EIA 1-5/8" Flange.
+ .001%
- 80 dB.
+ 100 kHz.
600 ohms.
+ 10 dBm, + 2 dB
+ 1 dB, 30-15,000 Hz.
or less, 30-15,000 Hz.
65 dB below 100% FM modulation.
50 dB below equiv. 100% AM modulation
208/240 V. 1 phase, 50/60 Hz,
3-wire service. 115 V, 1 phase
50/60 Hz.
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Input AC Power Requirement
Power Line Variation
Power Factor
Altitude
Ambient Temp. Range
Maximum VSWR
Overall Cabinet Size
Weight
Front Door Swing
2.6 KW, 208/240 V,
6 WI 115 V.
(slow) +5%.
71 500 ft.
-20° C to 45° C.
1.7 to 1.
29" W. x 78" H. x 33" D.*
600 lbs.
29".
*33" is overall depth dimension. With rear door,
front door handle, and meter trim strip removed
minimum depth is 30".
Filter and RF plumbing extends 5" above cabinet top.
1.6 Vacuum Tube
The following tube is employed in the transmitter.
V-1 4CX1000A Power Amplifier
SECTION 2
INSTALLATION
2.1 Inspection -
The FM-1H is carefully packed at the Gates plant to ensure
safe arrival at its destination. The equipment is packed
in a heavy carton and a wooden crate. Open the crate and
carton carefully to avoid damaging any of the contents.
Remove the packing material and search for possible loose
items such as pilot lights, fuses, loose screws and bolts.
If damage should occur during shipment all claims should
be filed promptly with the transportation company. If a
claim is to be filed, the original packing case and ma-
terial must be preserved. A damage report must be filed
to collect for shipping damages. Gates Radio Company is
not responsible for damage occurring during shipment.
Parts or components shipped to replace those damaged in
transportation will be billed to the customer plus trans-
portation expenses, the cost of which should form a por-
tion of your claim to the transportation company.
A complete visual inspection should be made of the equipment.
Determine that there are no loose connections, loose com-
ponents, broken insulators, etc., that may have been dam-
aged in shipment. Make sure all relay contacts are free
and in good mechanical condition. Make sure all mechanical
connections are tight. Check with a screw driver or a
wrench all mechanical and electrical connections that are
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mechanically bolted together. All tie downs or blocking
used for shipping purposes should be removed. A good
overall visual inspection may save time and trouble in
placing the transmitter into operating condition.
2.2 Packing Check List -
Certain components of the transmitter have been removed
for shipment and are packed separately to ensure safe .
handling. These parts on the FM-1H have been kept to a
bare minimum. The following components have been removed
from the transmitter for shipping purposes:
Quantity Part Number Description
1 700 0052 000 Portable Multimeter(VOM)
1 576 0029 000 Relay, Time Delay, K7
1 374 0015 000 Tube, 4CX1000A
1 524 0029 000 Cap., 80 mfd, 450 V. 04
1 992 1684 001 Low Pass Filter
1 620 0055 000 1-5/8" EIA Elbow
2.3 Installation -
In advance of actual placement of the equipment, certain
planning should be accomplished. Holes are provided in
base of transmitter for entry of power, audio and remote
control wires.
Either side of the transmitter may be placed against a
wall or other equipment. Complete accessibility for
maintenance and installation is provided in the FM-1H
by access from the rear of the transmitter cabinet.
Install the correct plug-in capacitor, C4, (80 mfd.) in
the transmitter screen supply. Also, install the time
delay relay, K7.
Refer to the TE -1 Exciter Installation Instructions for
proper module placement in the exciter cabinet.
The 4CX1000A must be fully inserted in the tube socket
before turning to engage the socket fingers. The anode
connector secures by a press fit to the tube and with a
screw to the plate coil. Handling of this tube is
covered in Section 2.4.
Bolt the 1-5/8 elbow between the directional coupler and
the low pass filter. Orient the filter in the desired
position and connect to the antenna coax. SuPPort must
be provided for the transmission line and low pass filter.
-4- FM-1H

2.4 Tube Handling and Operating Precautions, 4CX1000A.
Avoid bumping this tube. Due to its mass, bumping this
tube will introduce resultant stresses which may cause
internal damage.
Before operating this tube, please refer to the tune-up
and operating procedure given in Section 3. It is
recommended procedure to adjust the equipment for operation
under heavy plate loading conditions, and with only suf-
ficient RF drive to provide the required power output and
efficiency.
Extreme care should be taken during tune-up as well as
in regular service to avoid, even momentarily operation
of this tube under conditions of insufficient plate
loading or excessive RF drive. These operating condi-
tions,especially at the upper end of the VHF range, will
produce excessively high seal and/or bulb temperature
and will result in damage to this tube.
2.5 Power Connections -
After the transmitter is physically in place and the
components removed for shipment have been re-installed,
the audio and AC power EfaDull be brought to the transmitter.
The audio input line enters the base of the transmitter
in front of the fuseblock and connects directly to term-
inal board TB1 of the M-6425 exciter. Terminals 1 and
3 are the audio inputs and terminal 2 is ground or shield
connection. If stereo is used, the lines are connected
in accordance with the instructions in the M-6533 stereo
generator manual, which is a part of the M6425 Exciter manual.
The power leads from the transmitter should come from
a low reactance power source of either 208, 230 or 240
volts, 50/60 Hz, single phase with approximately a 3 KVA
capacity. The AC supply enters the transmitter in the
lower right hand corner and connects to the fuseblock.
The center terminal of the fuseblock is neutral or ground.
The conduit or wiring of the power leads should be in
agreement with local electric codes and be able to carry
the power requirements of the transmitter. Power leads
and program leads should not be run in the same conduit
or in the same wiring duct. If, due to necessity, the
program leads are in close proximity to the power leads,
the program leads should be separately shielded.
Connect 115 VAC to the exciter oven terminals 9 and 10
on TB1. This supply must be energized at all times.
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A good ground at these FM frequencies is mandatory in
keeping RF currents in nearby audio equipment to a
minimum. RF usually shows up in one of two ways--
feedback or high noise, and in some cases both. It
should be pointed out that even a small amount of
unshielded wire makes a very efficient antenna for FM
frequencies. If RF from the cabinet field is trans-
ferred to the grids of the audio equipment, it is recti-
fied and shows up as noise or feedback. We strongly
recommend a single common ground point from the trans-
mitter base to a good grounding system such as a water
pipe or actual earthing ground.
2.6 Cooling -
The transmitter is air cooled and approximately 2.5 KW
of heat are developed and dissipated through the air
outlet in the top of the transmitter. It may be nec-
essary to provide a means of exhausting this air from
the transmitter room or enclosure. Hear is a major
enemy to electronic component deterioration. A good
system of removing the heated air from the transmitter
and the transmitter room, and providing cool air for the
air inlet of the transmitter will greatly prolong the
life of the transmitter and its components. (2.5 KW
equals approximately 142 BTU/Min.)
There are many installation possibilities. Each and
every installation is somewhat different. Therefore,
it is not possible to give complete detailed information
on the transmitter cooling. Only general information
can be supplied. As a suggestion, contact a local
heating and cooling contractor for a detailed analysis
of the problem.
After the transmitter has operated at full output a
number of hours, a temperature rise inside the transmitter
must not exceed a rise of 20° 0 above the ambient measured
at the air intake of the blower and must not rise above
60° C under any circumstances. (20° C equals 68° F;
60° C equals 140° F).
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SECTION 3
OPERATION
3.1 Pre-Operation -
Before placing the FM-1H into operation, check once again
the points covered in Section 2. Have you mounted all
components physically and made these electrical connections:
1. Primary power to the fuseblock?
2. Program line connected to the exciter?
3. 115 volts for the crystal ovens?
4. Transmitter connected to antenna or a suitable load?
If everything appears to be in order, then you may proceed.
3.2 Test Data -
Your equipment has gone through many different kinds of
tests at the Gates factory and has been operated for several
hours on your assigned operating frequency. This is to
ensure correct adjustment and proper setting of all controls.
Refer to the test data supplied with your transmitter. This
data is attached to the front of the transmitter when shipped.
3.3 Adjustment -
Set the dial settings to those given on the test data sheet.
Primary power may now be applied to the transmitter by push-
ing the Filament ON button. The light behind the Filament
ON button should light. Next, the blower should begin to
run and come up to speed. After the blower reaches maximum
operating speed, air pressure in the P.A. enclosure will
operate the air switch. The air switch closing will allow
the filament voltage to be applied to the 4CX1000A. Adjust
the filament voltage for 6 volts according to filament meter..
After final tune-up the filament voltage can be lowered to
approximately 5.5 volts to extend tube life. However, this
should only be done without a loss of power output.
A three minute time delay prevents the plate voltage from
being turned ON immediately after the filaments are turned
ON. This allows the P.A. cathode to reach its operating
temperature.
Be careful when checking any voltages with the transmitter
filament ON.
The screen voltage motor is controlled by the Raise/Lcwer
switch on the front panel. Set the screen voltage to the
position indicated on the test data sheet.
NOTE: The Portable Multimeter (VON) supplied by the Gates Radio.
Company or an equivalent meter can be used for the tune-up
procedure.
—7— FM-1H

Check the bias voltage as indicated on the test data sheet.
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The Grid Tuning and Plate Tuning controls have a 25:1 gear
reduction. The scale divisions are set at the factory so
proper tuning will occur on the numbered sections of the
tuning knobs. Do not rotate the knobs 360° as this will
not return the capacitors to their previous position.
Check the dial setting of the Plate Tuning and Output Loading
with the test data information.
The rear door closes the interlock to allow the Plate Voltage
to be turned ON. Use extreme caution in operating the high
voltage supply with the door off.
Turn ON the Plate Voltage. Adjust the Grid Tuning for
maximum power output. Adjust the Plate Tuning and Output
Loading for maximum power output.
The Output Loading is generally set so a further increase
in plate current does not increase the power output. Due
to the operation characteristic of the amplifier, a plate
current dip may or may not appear when tuned for a 1000 watt
output. In a situation where plate current dip is not present
the Plate Tuning should be adjusted for best efficiency at
1000 watt output. Refer to complete tune-up procedure in
Section 5.4 for method used in preliminary tuning.
Check the VSWR on the transmission line. Position the
VSWR-Power switch on front panel to VSWR CAL and set VSWR-
Power meter for full scale deflection with the VSWR CAL.
control. Turn the switch to VSWR and read the reflected wave.
Although the transmitter will operate into a 1.7:1 mismatch,
it is recommended to keep the VSWR to a minimum. If a high
VSWR is noticed it is generally traced to transmission line
and/or antenna problems.
Since the transmitter was checked into a 50 ohm resistive
load, any system with a mismatch will probably change the
tuning. Therefore, the recorded test data knob readings
may not agree with actual operation.
The screen Raise/Lower control is used to compensate for
any supply line voltage variation which cause power output
fluctuations. The screen voltage will normally be operating
between +220 to 250 VDC.
Refer to the test data sheets of your transmitter for the
performance readings you can expect when the transmitter
is operating at 1000 watt output.
The input coupling capacitor, C35, is pre-set at the factory
and should not be adjusted under normal tune-up.
The operation of the transmitter is very simple and straight-
forward, and once adjusted should require only a nominal
amount of touching up the tuning at regular maintenance
periods

The overload is set for correct operating level at the
factory. The PA plate overload is set for approximately
.8 amperes plate current. The adjustment for the overload
is located under a small cover plate located on the front
panel. It is referred to as symbol number R13 on the schematic.
OPERATION AT OUTPUT POWERS BELOW 1000 WATTS
Power output of the transmitter may be decreased by
increasing the bias voltage and/or decreasing the R.F.
drive from the Exciter. It is best to leave the Output
Loading control and the Screen Voltage set as if the power
output was 1000 watts. The reduction in power output can
be accomplished in equal increments caused by the bias
voltage and the R.F. drive (i.e. for 800 watts output;
increase the bias for 100 watt reduction and decrease
R.F. drive for another 100 watt reduction). The Grid
tuning should be re-adjusted for maximum power output.
The output of the exciter is adjusted with an Output control
of the 10 W. amplifier in the exciter and is covered in
Exciter Manual.
The transmitter can easily be remotely controlled. Des-
cription of the connections are covered in Section 5.
3.4 Maintenance -
Maintenance of the FM-1H should consist of the following:
1. Keeping the transmitter clean.
2. Changing tubes when emission falls off.
3. Checking mechanical connections and fastenings.
4. Lubricating the blower motor.
Keeping the transmitter clean from the accumulation of dust
will reduce failure resulting from arcing, dirty relay con-
tacts, and overheating of chokes, resistors and transformers.
Electrostatic fields are "dust gathers". Support insulators
in the PA enclosure and other locations are the worst offenders.
They must be kept clean and free of all foreign material at
all times. If not, arcing may result and the insulator
shattered.
The air filter should be clean at all times. Periodically,
it should be discarded and replaced with a new one. The
filter is a disposable type and may be obtained from Gates
by Part #1 M8-0103-000 or any hardware or heating supply store.
Once a month the entire transmitter should be cleaned of
dust. The inside of the power amplifier should be thoroughly
wiped clean of dust. A small brush, soft rag, and vacuum
cleaner can be used very effectively in keeping the equipment
clean.
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All contactors and relays should be inspected regularly
for pitting and dirt. The contacts should be burnished
and cleaned if required. The overload relay is a telephone
type, with sealed contacts and should require little atten-
tion.
The bearings for the motor of the PA blower should normally
give long trouble-free operation. Periodically, oil should
be added for lubrication.
The PA tube should be removed once a month and the fins
cleaned of dust. Air may be blown through the fins in
the reverse direction or the anode cleaned with soap and
water or denatured alcohol.
This transmitter is a precision electrical device, and as
such, should be kept clean at all times and free of dust
and foreign materials. Dust and moisture condensation will
lead to possible arcovers and short conductive paths.
A good preventive maintenance schedule is always the best
assurance for trouble-free transmitter operation.
SECTION 4
CIRCUIT DESCRIPTION
The FM-1H circuits will be described in the following
sections:
Power Amplifier.
Exciter.
Power Supply.
Control Circuits.
Metering.
4.1 Power Amplifier -
The power amplifier of the FM-1H employs a single 4CX1000A
tube in a common cathode amplifier circuit. The plate cir-
cuit is a modified "pi" which uses a capacitor for fine
plate tuning. The plate coil inductance is made variable
with the movable shorting strap to set the coarse tuning.
The Grid circuit is capacity tuned. A diode has been placed
in the bias lead to prevent the control grid from drawing
grid current due to R.F. excitation. R29 and R30 are used
to lower the circuit Q for better stability.
Neutralizing is accomplished by plate to grid feedback. The
position of the capacity plate, C10, determines the amount
of feedback. Once the neutralizing is adjusted, it should
not require any adjustment under normal day-to-day operation.

e
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The input loading capacitor, C35 is used to obtain a good
match between the exciter and PA. 035 is set at the factory
and should not require any adjustment.
4.2 Exciter -
The FM exciter is described in detail in the exciter
instruction book.
4.3 Power Supply -
The high voltage power supply furnishes 3 KV for the power
amplifier. The basic configuration of the supply is single
phase, full wave with a two-section choke input filter. The
rectifiers consist of two separate columns mounted on the
base of the cabinet. *
The bias supply is single phase full wave circuit using
silicon rectifiers. Grid bias between 0 and -100 volts is
supplied to the control grid. The bias control is mounted
on the front panel.
The screen supply is a single phase full wave configuration.
Voltage variation from 0 to +270 volts is available from the
motor driven control. The variations are controlled by the
Raise/Lower switch on the front panel.
* The primary taps on teh plate trnsformer, T2, may have
to be changed to compensate for input line voltage
variations.
4.4 Control Circuits -
The control circuits of the FM-1H consist of the following:
Kl - Primary Contactor - applies voltage to the filaments,
exciter, and energizes the blower.
K2 - Plate Contactor - applies primary voltage to the
plate transformer.
K3 - Remote Screen Control Relay - permits raising and
lowering the screen voltage remotely.
K4 - Auxiliary Relay - applies holding voltage to K2, if
the air switch and door interlock are closed.
K5 - Recycle Relay - energizes when the PA overload
relay is energized a number of times. The number
of times is determined by control R24. The over-
load relay contacts are in parallel across the relay
circuit for K5. When the 0.L. relay energizes and
the contacts open, C19 starts to charge. If the
contacts are open for a sufficient length of time
for 019 to charge to the point that the voltage will
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energize K5, the contacts of K5 will break the
hold circuit of K4 and the plate voltage will be
switched OFF. If K5 does not operate, the over-
load contacts will close after an overload and the
.plate contactor, K2, will again energize.
K6 - Plate Overload Relay - adjusted to interrupt the high
voltage when excessive plate current is indicated.
K7 - Time Delay Relay - allows cathode of the 4CX1000A
to reach operating temperature before high voltage
is applied.
Sll - Air Switch - closes after the air pressure in the
plenum reaches proper pressure, closing the inter-
locking circuits and switching primary voltage to
the PA filament transformer.
4.5 Metering - `
All necessary metering of the FM-1H is accomplished with
four meters located on the cabinet meter panel. Filament
voltage is indicated on the first meter from the left on
the meter panel. The voltage is controlled by the
"Filament Adjust" mounted on the front panel.
The second meter reads PA plate current and is located
in the Plate B+ lead. The meter is properly insulated
and isolated behind a protective plexiglass cover.
The third meter reads plate voltage and is located on the
low potential side of the meter multiplier resistor.
The fourth meter is for indicating power output and VSWR
on the transmission line. This meter works in conjunction
with the directional coupler mounted in the output trans-
mission line.
SECTION 5
ADDITIONAL INFORMATION
5.1 Remote Control -
Remote control facilities are built into the FM-1H and
require only connection to either the Gates RDC-10 remote
control unit or the Gates RDC-200A remote control equip-
ment. The connections to the transmitter are made at
TB-2 and TB-1 located on the back of the front panel.
Terminal connections for the functions are shown on the
schematic.
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The functions are:
1. Fail-Safe, Primary ON-OFF.
2. Momentary ON-OFF for plate voltage.
3. Raise/Lower for adjusting power output.
4. Plate voltage metering.
5. Plate current metering.
6. RF power output metering.
The controls for setting the remote plate voltage and
plate current for external metering are located under
the cover on the front panel and are shown by symbol
number on the schematic.
The screen voltage of the power amplifier is motor
controlled and is also connected to the remote control
Raise/Lower function for power output adjustment.
The M4845 Remote Power Output unit will provide R.F.
monitoring.
5.2 Stereophonic Operation -
Provision has been provided for the installation of the
Gates M6533 Stereo Generator in the FM exciter.
Instructions for audio and RF connections are given
in the M6425 manual.
With the addition of the M6533 Stereo Generator, the
transmitter is FCC type accepted for stereophonic operation.
5.3 Spare Oven and Crystal
Refer to FM exciter instruction book.
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