TM 55-1930-209-14&P-12
filter which employs aluminum slugs for insuring high Q. It is then amplified by a J-FET common gate amplifier
(QlO1) and again filtered through a high Q bandpass filter.
2.
First Mixer
After the initial amplification and filtering, the signal is applied to the gate of the first mixer transistor (Q102) while
the first local signal is injected into the source of the mixer transistor. This permits the mixer stage to have a wide
dynamic range. The first local frequency is obtained by the following formula.
First Local Frequency = Receive Frequency - 21.40 MHz
3.
First And Second IF
The heterodyning action of the first mixer produces a 21.4 MHz intermediate frequency, which is filtered by a
crystal filter (F201), then passed to the second mixer (Q201). The first IF signal is mixed with a 21.855 MHz signal
at this stage to produce a 455 kHz intermediate frequency (second IF).
The 455 kHz signal obtained at Q201 is fed through the second IF filters
(F202 and F203), then amplified by limiting amplifiers Q203 and Q251.
4.
Discriminator
A conventional FM discriminator (L251, L252, Q252, and Q253) is placed after the above stages to recover the
audio signal from the modulated RF signal. The audio signal is amplified by Q351 to obtain the power to drive the
speaker.
5.
Noise Squelch
A noise-actuated squelch circuit consisting of a noise amplifier/limiter (Q301), noise detector (Q302 and Q303),
and a DC control circuit (Q304 and Q305) is included in the receiver to cut off the audio amplifier. This eliminates
static which would otherwise be heard at the speaker during intervals between received messages.
MAINTENANCE
GENERAL
The inherent quality of the solid-state components used in the transceiver will provide many years of continuous use
without failure, assuming the unit is treated with care. The following precautions should always be observed to pre- vent
damage to the radio.
1.
Never key the transmitter unless an antenna or suitable dummy load is connected to the antenna receptacle of the
radio.
2.
Avoid excessive supply voltage. The voltage should not exceed 16 VDC, nor should it fall below 11 VDC.
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