Hammarlund FM50A - Operation and Installation Procedures; Unit Description and Operation

DESCRIPTION
1"-"
The FM-50-A is a rugged, compact communications unit designed to operate from any
6 or 12 volt d. c. (negative or positive ground) vehicle power source or a 117 volt a. c. 50 to
400 cycle land station power source.
The FM-50-A is designed for narrow-band phase/frequency modulation (±5KC deviation)
operation in the frequency range of 147 to 174 megacycles. The receiver and transmitter sections
are designed for single channel, crystal controlled operation. The transmitter and receiver may
be operated on the same channel (as in the business radio service) or on different channels (as in
the taxicab radio service).
All necessary components for 6 or 12 volt d. c. operation of either polarity or 17 volt
AC operation are built into the basic communications unit. The proper circuitry is selected
by the wiring of the external power plug thereby eliminating the need for jumpers or switches
in the basic unit. The FM-50-A may be interchanged in any 6, 12 or 117 volt system without
modific ation.
OPERATING INSTRUCTIONS
Control Functions: There are only three external controls. The left knob is a con-
ventional volume control; the right knob controls the squelch. By turning the squelch knob
clockwise, the sensitivity is increased and as this control is advanced clockwise, a point will
be reached beyond which a loud hiss will be heard. However, there is a setting before this
point where the receiver is operating at optimum sensitivity in a squelched (noiseless) condition.
The three-position power switch on the panel is "OFF" in the extreme left setting. In
the center, or "STDBY" position, the receiver only is operating, and the transmitter filaments
are turned off. In the "OPERATE" position, the receiver remains "ON" however the trans-
mitter filaments are also "ON". After a warm-up period of about 20 seconds, the transmitter
is ready for operation by depressing the "push-to-talk" switch on the microphone.
The "on-off" pilot lamp located to the left side of the power switch lights when the set
is turned on. The pilot lamp on the right side lights only when the transmitter is on the air.
When the push-to-talk microphone switch is depressed, the transmitter section of the
communication unit is actuated, the red transmit lamp lights and the receiver is muted.
Release of the push-to-talk switch, turns the transmitter section off, extinguishes the red
transmit lamp and actuates the receiver section. This sequence of events is in the "OPERATE"
position of the power switch. When this switch is in the "STDBY" position the microphone push-
to-talk circuitry is inoperative.
The use of the "STDBY" mode of operation is highly recommended where long periods
of listening only is expected as lower power drain together with longer transmitter tube life
will result.
The FM-50-A is a highly efficient receiver-transmitter and will provide reliable com-
munications over great distances if properly used. Radio operating is an art that is easily
learned with practice.
The limitations of a system installation in any particular area can be learned through
use. Every system, regardless of the frequency or power, will have some locations where it
is not possible to communicate. However, within its range, trees, buildings, small hills and
similar obstructions will have little or no effect on communications. The range of a system is
dependent on a few important factors, such as location and height of base station antenna power,
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