antenna tuner applies a Tune In Progress
ALC In (Figure 2-7).
audio control hybrid A4, the ALC In is
signal to the ALC time constant switch.
routed to the ALC Off/On.
voltage from the ALC offset adjust deter-
PA OFF/ON Control.
mines the threshold at the ALC amplifier.
describes the PA OFF/ON control logic.
The time constant of the ALC amplifier
The PA OFF/ON control is used with other
output is adjusted by the ALC time con-
configurations of the receiver/ exciter,
but not the AN/PRC-104.
This occurs when the
- (3.5 ma)
OFF - (0 ma)
Receive Audio becomes the To Vol Control
signal which is fed back to the audio
control hybrid to control the output of
Third Converter A3.
operation, relays K1 and K2 are ener-
the receive audio amplifier.
gized by the +28v Xmt Enable and by the
mode, a 100-microfarad capacitor is
Keyline ground signal.
This permits the
switched out, which shortens the time
constant on the agc generator output.
Xmt Audio to be mixed with the 5-MHz LO
(amplified by Q1) at mixer U4 via the
Finally, the 5-MHz if. mixes with the
energized contacts (3-2) of K2.
5-MHz LO to create the audio frequency
MHz mixing product goes to the sideband
and upper sideband mixing product at
filter FL2 via the energized contacts
(7-8) of relay K2 and contacts (7-8) of
relay K1. The energized contacts (2-3)
Sideband Filter FL2.
of relay K1 also route +12.5v to the
filter functions identically in receive
The +12.5v Xmt also
and transmit operation.
turns switch Q6 on, which causes +6.5v
rejects frequencies other than 4.9970
Xmt to be applied to the second con-
to 409997 MHz.
verter A2 and the audio control hybrid,
In receive operation, the relays
are not energized so the 5-MHz if. goes
through amplifiers U1 and U2 and +12.5v
operation, relay K1 is energized by the
is applied to Zener diode VR1 (which
+28v Xmt Enable and by the Keyline sig-
breaks down at +6.5v). The gain of the
The 5-MHz if. goes through match-
5-MHz if. is controlled at U2 and U1 by
ing transformer T1 and to amplifier U2;
the agc voltage from the agc generator
the level (amplitude) of the entire
U3. This agc voltage is also applied to
modulator/demodulator transmit output
the second frequency converter via FET
is controlled at this amplifier by the
Q7; FET Q7 conducts when the +12.5v Xmt
ALC signal from the audio control hybrid
enable is absent at the gate (G). The
A4 and by the presence of the +6.5 Xmt
agc generator, in turn, is controlled by
The 5-MHz if. is applied
the Rcv agc receive audio signal from
to mixer U4 where it mixes with the
the audio hybrid.
A portion of the agc
70/80 MHz LO. (The 70/80-MHz Lo has