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OCUBIC
COMMUNICATIONS
S"".ItI
DIVISION
MICROPHONE PREAMPLIFIER
C 1 2 } 4 TO
vax
0105
MIC
LEVEL
TO UI04C
+
-=
I.
CI23
"115.
C"".
C""7
Cl"
TO
4C;l--4"+-tt-o
MIe . . . .
into conduct ion
switch UI09
aff.
IC.
The farmer
+lIV
TX
AUDIO
SPEECH
PROCESSOR
SPEECH PROCESSOR
The audio signal from the microphone or external input jack is coupled
through RIJJ or RIJ5, respectively, to blocking capacitor C122 and thence to
the base of microphone
preamplifier QIOJ.
Cl19 and C120
are RF bypasses,
while bias is developed from the collec-
tor by voltage divider
RIJ4-RIJ6.
This
provides
feedback
to keep the
gain of
the stage fixed.
The emitter circuit is
standard,
composed of resistor RIJ7 and
bypass capacitor C12J.
Output is
coup-
led via
C124 to the VOX circuit and to
the internal microphone level control.
I
When the operator desires to use the
built-in speech processor,
a voltage is
applied, through voltage divider R150-R151, that biases QI07
thus lowering its collector voltage and turning section
A
of
This in turn activates
sections Band C of that
switching
turns
section D off,
opening
the
feedback
path
for UlO4C
composed of R15?, and the lat-
ter completes the
alternative
feedback path composed of R15B,
CRl17 and CRIIB.
Ulo4C,
in this case, op-
erates as a compressor.
When
signal peaks at
the output of
the amplifier
exceed the
har-
rier potentialof
CRl17
and
CRl18 (+ 0.7 volt) these peaks
are fed back
to the inverting
input of that amplifier,
thus
reducing
its gain.
When spe-
ech processor operation is not
desired,
R157 is
utilized as
the feedback path,
converting
UI04C into
an ordinary fixed-
gain amplifier stage.
MODULATION AMPLIFIER
Ul04D is a fixed-gain amplifier,
immediately following the front panel
MIC GAIN controle
Feedback is provided
by
the
R162-CIJ5 parallel combinat-
ion, with CIJ5 providing additional feedback at the higher audio frequencies
thus reducing gain of the stage in that range, and providing a more pleasant
4-1
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