TM 11-6625-2629-14&P
discriminator is displayed. In the FINE TUNE
5-5. Mixer CR1
position, carrier shift up to 250 kHz is displayed.
R e s i s t o r s R73 and R74 are in series with the
The crystal mixer CR1 receives the oscillator
CARRIER SHIFT meter to limit current through
signal and the rf signal; the resultant if signal is
the meter. Resistor R75 is a calibration poten-
fed to the first stage of if amplification. The
tiometer for the FINE TUNE position of S4.
oscillator signal is injected through R 1, which
p r o v i d e s signal separation from the local
5-9. Audio Amplifier V10, V11, V12, and V13
oscillator, to diode CR1.
5-6. 1st If Amplifier V2 and Integrated Circuit
The audio amplifier circuit (V10, V11, V12, and
U1
V13) is comprised of four resistor-capacitor (rc)
coupled stages. The low-distortion, high-stability
circuit has a cathode follower input and output.
If amplifier stage V2 and integrated circuit U1
The signal inputs from the discriminator are
form a high-gain, wide-band circuit operating at a
amplified and fed to DEVIATION meter M3 and
center frequency of 12 MHz with an overall
the AUDIO OUTPUT terminals.
bandwith of 3 MHz. The if amplifier V2 rejects
a. Tube V10 is the cathode follower input and
undesired output frequencies of the mixer and
first audio stage. Operating bias for V10A is
provides primary amplification for integrated
developed by the drop across R79. Attenuation of
circuit U1. IC U1 has the ability to accommodate
the audio output of V 10A is obtained by tapping
a wide range of input signal level, and eliminates
the need for automatic volume control.
off a fixed portion of the voltage applied to the
voltage divider consisting of R78, R82, R83, R84,
5-7. Limiters V7 and V8 and Driver Amplifier V9
and R85. This effectively varies the range of the
DEVIATION meter. Capacitor C85 provides
Limiting is achieved by grid limiting action in
coupling from V 10A cathode to the attenuator
stages V7 and V8. The two stages are used to
circuit. Coupling from the attenuator to the grid
obtain the required amplitude-modulated (am )
of V10B is through C86. The cathode of V10B is
rejection characteristics. The signals from the
tied to the voltage divider in the cathode of V12.
amplifier stages are limited and fed to the driver
The cathode voltage is raised or lowered as
amplifier stage V9. The grid return for V7 is R50,
necessary to give constant gain throughout the
which is in series with LIMITING meter M 1.
amplifier circuit. A bypass circuit in the plate of
L I M I T I N G A D J c o n t r o l R 5 1 s e t s the
V10B, comprised of R89 and C88, is used to short
LIMITING meter to the start of the black area
frequencies above the audio range to ground.
when the signal input level to the equipment is 5
Signals from the plate of V10B are coupled to the
millivolts. Capacitor C54 is the bypass for the
grid of V11 through C106.
LIMITING meter.
b. Tubes V11 and V12 are conventional audio
5-8. Discriminator T9
amplifier stages. Operating bias for V12 is
developed by the drop across R105 and R106. The
junction of R105 and R106 is the return for the
The discriminator is a modified Fester-Steel type
cathode of B10B. Two outputs are taken from this
and is completely enclosed in the. can for trans-
stage. The signal from - the plate is coupled
former T9. The discriminator receives the signals
through C94 to the grid of V13A. The signal from
from the driver amplifier and converts the in-
the junction of R103 and R104 is coupled through
formation to an audio signal with its amplitude
C98 to the grid of V13B.
determined by the amount of deviation from the
c. Tube V 13 provides two cathode follower
carrier frequent y. This audio signal is then fed to
output stages. The cathode load for V13A is
t h e audio amplifier circuits. Resistor R66
R112. Coupling from the cathode of V13A to the
broadens the response of the transformer primary
DEVIATION meter rectifier circuit is through
to accept 10.5 to 13.5 MHz. Capacitor C81 acts as
C96. Rectification of the audio signal is achieved
a stabilizer to keep the dc level constant when no
deviation is present. Carrier shift indication is
by CR7 and R113. Resistor R116 limits current
through the meter. Meter calibration is obtained
displayed on CARRIER SHIFT meter M2. The
by the setting of CAL ADJ R118. Grid bias for
deflection of the meter is proportional to the
voltage at pin 3 of the discriminator. Two ranges
V13B is developed by the drop across R117.
Operating bias is developed by the drop across
of carrier shift are available by use of the TUNE-
FINE TUNE switch S4. In the TUNE position
R115. The load for the cathode of V13B is
comprised of R119, R120, and R121. Resistor
(positions shown) of S4, the entire S-curve of the
5-4
