Hammarlund FM50A - Service, Alignment, and Updates; Transmitter Tune-Up and Test Equipment

and nature of surrounding terrain. The use of a high gain type of antenna at the base station is
highly recommended in all installations for best possible performance.
Assuming that the most efficient installation of the FM-50-A is made, one important
consideration remains. This is correct operating procedure and a few important notes in this
regard are:
L Before transmitting, listen to the receiver and make certain no one else is on the
channel.
2. Let the mobile operator get in the practice of calling the base station for instructions.
Since the base station is in a known, fixed location, the mobile operator can call when he knows
he is in a good location.
3. Show each mobile operator how radio actually helps him in his work by eliminating
doubts about delivery, reducing unnecessary travel, etc.
4. If you are trying to contact a mobile unit from the base station, remember that he
may be in a poor radio-location, he may have both hands busy in heavy traffic, or he may have
stopped in the local diner. If you do not contact him after one or two quick calls, wait a few
minutes before calling again.
5. Keep messages short and brief. Know what you are going to say before you depress
the microphone button. Many 100 word discussions can be reduced to 10 word messages by
thinking and planning before going "on-the-air".
6. Adopt a system of routine and preventative maintenance with your serviceman.
7. Become familiar with the F. C. C. rules and regulations concerning operation of two-
way radio for your particular class of service.
Transmitter Tune- Up Procedure:
CAUTION - The plate capacity of the 6146 output stage is "hot" at all times when power
is turned ON. This applies to both the "STANDBY" and "ON" positions of the power switch.
The transmitter duty cycle is one minute on, four minutes off; therefore, all adjustments
should be made as quickly as possible, keying the transmitter only when ready for actual adjust-
ment or measurement. To minimize interference, on-the-air testing (with antenna connected)
should be kept to a minimum. The use of a 50 ohm dummy load is recommended for all but the
final on-the-air use of the equipment.
If extended periods of testing and/or servicing the exciter stages of the transmitter are
required it is recommended that the lead connecting R150 and R151 be opened. All tests up to
and including the grid of the final stage can be made.
Test Equipment Required:
1. 0-100 micro-ammeter (2000 ohm internal resistance) see page 21 for recommended
test meter circuit.
2. RF wattmeter with 52 ohm dummy load.
3. Modulation deviation meter.
4. Frequency meter with an accuracy of at least. 00025%.
(a) With a
0-100 micro-ammeter connected from terminal 2 of J105 to ground (terminal
11) adjust L118 for maximum indication. (position 2 of recommended test meter)
(b) With the micro-ammeter now connected from terminal 3 of J105 to ground, adjust
L1l7 for maximum indication. (position 3 of recommended test meter)
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