a. the emission is too low.
b. the circuit becomes unstable.
c. a potential must exist between the two cathodes.
d. high-frequency interference distorts the output.
4. Assume that an AFC system similar to that shown in figure 82 of TM 11-668
uses the basic phase discriminator shown in figure 87 in place of the mixer and
discriminator.
A positive output voltage of the discriminator indicates that the
multiplied input frequency from the master oscillator is
a. equal to the crystal oscillator frequency.
b. less than the crystal oscillator frequency.
c. greater than the crystal oscillator frequency.
d. In phase with that of the crystal oscillator.
5. In the AFC system shown in figure 93 of TM 11-668, a multivibrator is used in
the block labeled
a. PHASE SHIFTER.
c.
MASTER OSCILLATOR.
b. FIRST DIVIDER.
d.
BALANCED MODULATOR.
6. Assume that a signal with a frequency of 440 kHz is to be divided by 4. The
oscillator that is to be synchronized by this voltage must have a free-running
frequency of
a. less than 110 kHz.
c.
between 221 kHz and 440 kHz.
b. between 110 kHz and 220 kHz.
d.
greater than 440 kHz.
7. The stages in the AFC system in figure 100 of TM 11-668 include a
a. driver, mixer, and double-tuned discriminator.
b. crystal oscillator, mixer, and phase discriminator.
c. multivibrator, frequency divider, and pulse discriminator.
d. harmonic generator, discriminator, and reactance modulator.
8. Compared with a double-tuned phase discriminator, the advantages of a pulse
discriminator include
a. more accurate timing, no frequency-divider circuits, and no stabilizing
circuits to tune.
b. no frequency-divider circuits, no stabilizing circuits to tune, and no
limiter stages.
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