TM
11-5820-922-40-1
2-25. During normal receive operation,
At subtracter AR4, if the non-
2-21
q
inverting input (syllabic rate) is
the squelched audio is routed to opera-
tional amplifier AR6. The output of AR6
greater than the inverting input (signal-
plus-noise level), the voice gate con-
(approximately 10 milliamperes) is not
trol output will be positive. The mag-
large enough to drive the loudspeaker,
nitude of the positive voice gate signal
so the 10-milliampere audio signal is
routed to the complementary symmetry
is proportional to the voltage differ-
push-pull amplifier. This amplifier,
ence between the inputs to subtracter
consisting of Q5 and Q7, and Q6 and Q8,
AR4
If the inverting input (signal-
q
boosts the Rcv Audio to approximately
plus-noise) to AR4 is greater than the
1 watt. At this point the audio signal
noninverting input, the voice gate out-
put will drop to zero.
is called Amplified Rcv Audio, before
being applied to the loudspeaker. When
no signal is being received and the
squelch is on, a -30-db noise signal is
routed to the loudspeaker which produces
applied to voice gate control AR5 which
a slight hiss to assure the operator
develops a Squelch Control signal. The
that the equipment is still operating.
Squelch Control signal is used to con-
trol audio gate U3 as follows:
2-26. The dc power from the vehicle sys-
1.
If the syllabic rate input to AR4
is larger than the signal-plus-
tem is routed through the rf amplifier
noise input, the voice gate will
to the series dc limiter circuit (Q1,
turn on AR5 which outputs a high
Q2). The series dc limiter protects the
receiver/exciter from overvoltage and
Squelch Control signal and gates
on U3. Rcv Audio In is then
transient voltages. If the dc power
goes above +33v, the series dc limiter
routed through U3 and is output
as squelched audio.
will limit the voltage applied to the
receiver/exciter.
If the voltage
2.
If the signal-plus-noise is larger
remains at +33v, the series dc limiter
will remain saturated (inoperative),
than the syllabic rate, the voice
and the output voltage level will be the
gate is low, the squelch control
same as the input. Protection from
is low, and the audio gate is cut
off. In this condition, Rcv Audio
polarity reversal is provided by CR1
before +28v Battery is applied to the
In is not passed through audio
gate U3.
series regulator (Q1, Q2, and VR1).
the Squelch Control signal from going to
exciter is routed to power supply U1.
audio gate U3 when squelch operation is
The outputs of U1 are +12v and +6.4v and
not selected. When this condition
are used in this card. The +12v signal
is also routed to the TTY-FSK converter.
exists, Rcv Audio In is routed around U3
to the handset or loudspeaker.
The TTY-FSK converter serves as an inter-
2-24. The PTT signal from the handset
face unit between the teletypewriter and
the receiver/exciter. The TTY-FSK con-
cuts off audio gate U3 and variable gain
amplifier AR3 during transmit operation.
verter demodulates the Rcv Audio before
A small portion of the Xmt Audio signal
it is routed to the teletypewriter and
is routed back through audio gate U3 and
modulates the transmit teletypewriter
buffer Q4, and out to the handset
signals before they are routed to the
receiver as Sidetone/Rcv Audio.
receiver/exciter.
