TM 11-5826-225-35
rived from a 11O-CPS oscillator. The synchron-
ous filter causes the junction connection of ca-
pacitors C76 and C77 to assume the character-
istics of an LC filter tuned to a center frequency
of 110 cps. There is maximum signal transfer
1-17. 110-Cps Variable Phase Signal and
at 110 cps with response falling off at frequen-
Synchronous Filter
cies above or below this frequency.
c. The phase of the 110-CIM signal applied
a. The 110-cps variable phase signal and
through capacitors C76 and C77 to the collectors
other audio frequencies modulating the 142.5-kc
of Q19 and Q20 may be in-phase, or out-of-
IF amplifier frequency, are detected by age rec-
phase, with either one of the 110-cps signals
tifier CR3 and applied to the base of first age
applied to the bases of Q19 and Q20, Assume
amplifier Q16. In addition to serving as an age
rectifier for audio frequencies (para 1-16),
that phase 1 on the base of Q20 is positive-
diode CR3 also detects the 110-CPS variable
going, and phase 2 on Q19 is negative-going.
Every half cycle, these phases will change while
phase modulation envelope originally developed
the 110-cps variable phase signal may or may
in the balanced modulator (para 17). The 110-
not change phase at the same time. If the 110-
cps signal output of CR3 appearing in the same
phase on the emitter of Q16, is applied through
cps variable phase signal on capacitor C77 is
R145, C75, R66, and C125 to the servoamplifier
positive-going and in phase with phase 1 of the
furnishing power for the servo motor geared to
110-cps signal on the base of Q20, transistor
a resolver. Since undesirable audio frequencies
Q20 will conduct current from emitter to col-
other than 110 cps may be present, a 110-cps
lector and charge capacitor C77 until either
synchronous filter is used to remove these fre-
phase 1 of the 110-CPS signal reverses or the
quencies.
110-cps variable phase signal changes phase.
During the charging cycle, the emitter-to-col-
b. Transistors Q19 and Q20 operate as an
lector resistance of Q20 is low, and the current
electronic switch gated and synchronized by two
flowing from negative (ground) to positive
opposite phases of 110-CPS sine wave signals de-
Figure 1-8. Receiver agc and muting circuit,
1-16 Change 5
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