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_CUBIC
COMMUNICATIONS
SIIWAItI
DIVISION
which filters out any undesired mixer products.
Q124,
in series
with the signal path,
acts as
a switch to
cut off the
receiver output
AF when in the
transmit
condition.
In that
instance,
the "R" line
would be
low,
grounding the gate of Q124 and causing it to act
as an open circuit.
R2l9 and R220
provide bias volt-
age for the
source and
gate.
Output of
the AF mute
gate is then coupled via C2l0 to the base of AF ampli-
fier Q125,
which
provides additional
gain.
Bias is
conventional,
while
the emitter resistance is
only
partially bypassed to set the gain (see the "Servicing
Hints" section of this manual
for a discussion of fe-
edback amplifiers
such as this).
Output is taken via
C2l), while C2l4 provides
a degree of
high frequency
rolloff for more pleasing audio response.
+.v
A.F.
PREAIIIP
RIOZ
A
•
RI77
RI7lI
0-
OUT
CI45
....- i
I---4I
CI4 '
MOTCH FILTER
~:
0-........""""'........
--1
NOTCH FILTER
•
Audio from
Q125
is
applied to CR12) and CR-
124, which act
as a lim-
iter,
effectively
clip-
ping off any
peaks exce-
eding approximately ±O.7
volt.
The R172-C14) com-
bination filters the out-
put of
the
clipper
and
shapes the
audio response.
UlOlC is connected
as a voltage follower, pro-
viding drive for active filter UlOlD that is the same amplitude and phase as
its input, but of a lower driving impedance.
Cl44 and R178,
with R120A on the front panel, form the series leg of a
Wein bridge,
while C145, R177 and RlO2B
(also on the front panel) form the
shunt leg of the same Wein bridge.
This bridge is inserted in the inverting
feedback loop to form a notch when combined with
the normal audio frequency
applied to the non-inverting input of amplifier UlOlD.
R176 and R174form a
positive feedback path to raise the"Q" of the circuit.
Aumo
POWER AMPLIFIER/RECEIVER MUTE
Audio from
the output of
the notch
filter is applied to the high side of the
front panel volume control, and its wiper
is returned,
through R127,
to the input
of audio power amplifier UlO).
R129 acts
in conjunction with R127 as a voltage di-
vider.
Receiver mute switch Q104 is con-
nected between this input and ground, th-
rough isolating capacitor Cl17.
When
in
the receive
condition,
a voltage on the
"R"
line holds
Q104 in the "open" eon-
dition,
allowing the signal to
be
ampli-
fied
by
UlO);
when in the
transmit con-
dition, the "R" line is grounded, turning
Q104 "on" and shunting the signal to gr-
"ROM
VOL. WIPER
+
I
6V
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