S7902E. The 16 volts dc is supplied to the
4. Amplifier, 11.5-Mc
audio amplifier or one of the rf amplifiers
and the test probe rf preamplifier from
The 11.5-mc amplifier is a two-stage,
S7902E.
intermediate-frequency (if.) amp1ifier.
The overall gain of the two stages is about
3. Audio Amplifier
40 decibels (db). Power, input, and output
connections to the 11.5-mc amplifier are
The audio amplifier is a three-stage,
made when selector switch S7902 is in
direct-coupled, class A amplifier. Power,
position 7, 9, 13, or 14. The output from
input, and output connections to the audio
the 11.5-mc amplifier is rectified and fed
amplifier are completed when the selector
to the Schmitt trigger circuit.
switch S7902 is in position 3, 4, 5, 6, 10,
a. The input signal from the test probe
or 11. The output from the audio amplifier
rf preamplifier is limited b y resistor
is rectified and fed to the Schmitt trigger
R7612 and coupled to the primary winding
circuit.
of transformer T7601 through capacitor
C7601. Resistor R7613 matches the im-
a. The input signal to the audio ampli-
pedance of the test probe rf preamplifier
fier, developed across resistor. R7401, is
to that of the 11.5-mc amplifier input.
coupled through capacitor C7401 to the
b. First 11.5-mc amplifier Q7601 is
base of transistor Q7401. The amplified
connected in a common-emitter amplifier
output at the collector of transistor Q7401
stage which provides about 20-db gain.
is directly coupled to the base of transistor
Q7402. Resistors R7402 and R7403 form a
(1) Transformer T7601 and capacitor
voltage divider which develops the emitter-
C7602 tune the input to Q7601. The
base bias for transistor Q7401. Resistor
input signal is coupled to the base
R7404 is the output load resistor in the
of transistor Q7601 through capac-
collector circuit of Q7401.
itor C7603. The output signal from
Q7601 is developed across a tuned
b. The output at the collector of tran-
circuit consisting of the primary
sistor Q7401 is amplified by transistor
winding of transformer T7602 and
Q7402. The output of Q7402 is applied
capacitor C7608. Resistor R7604
directly to the base of transistor Q7403.
reduces the Q of the tuned circuit
Resistor R7407 is the emitter load re-
to provide the proper bandwidth.
sistor for transistor Q7402.
(2) Resistors R7601 and R7602 form a
c. The voltage divider, network consist-
i n g of resistor R7405, potentiometer
voltage divider which provides the
R7406, and capacitor C7402 develops de-
fixed-bias portion of the emitter-
generative alternating-current (at) feed-
b a s e bias for Q7601. Resistor
back for these directly coupled amplifier
R7603 establishes the self-biasing
stages. Potentiometer R7406 is a preset
portion of the emitter-base bias
control; its setting determines the overall
and stabilizes the emitter current.
gain of the audio amplifier.
Capacitor C7607 is an rf bypass
capacitor. Capacitor C7606 neu-
d. Resistor R7408 establishes the self-
tralizes the first 11.5-mc ampli-
biasing portion of the emitter-base bias
fier. Diode CR7601 prevents the
for transistor Q7403. Capacitor C7403 is
emitter-base bias from reversing
an audio bypass capacitor. Inductor L7401
when a very large input signal is
is the collector load for transistor Q7403.
applied to the stage. Capacitor
e. The output of the audio amplifier is
C7604 and inductor L7601 form a
coupled through capacitor C7404 to recti-
decoupling network in the 16-volt
fier CR7404. Resistor R7409 is the diode
dc supply line.
return resistor, R7410 is the load resistor,
and C7405 is the filter capacitor. The dc
c. Second 11.5-mc amplifier Q7602 is
output from the rectifier circuit is fed to
connected in a common-emitter amplifier
stage which provides about 20-db gain.
the Schmitt trigger circuit.
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