5. When an audio signal is applied, the reactance-tube modulator adds an
inductance to the oscillator tank circuit.
The amount of inductance injected by
the plate load is
a. 100 millihenry (mh).
c.
10 mh.
b. 50 mh.
d.
1 mh.
6. In the reactance-tube modulator represented by figure 38 of TM 11-668, Za is
always made large in respect to Zb because it controls the phase of the current
through the plate load.
The frequency deviation of a transmitter utilizing this
circuit is controlled primarily by the value of
a. impedance in Za
b. impedance in Zb.
c. tank circuit components L and C.
d. transconductance of the reactance tube.
7. Assume that in figure 38 of TM 11-668 the box labeled Za represents a 50-
picofarad (pf) capacitor, and the box labeled Zb represents a 1,000-ohm resistor.
If the modulator tube has a transconductance of 7,000 micromhos, the reactance
component injected into the oscillator tank circuit is equivalent to a
a. 350-uh inductor.
c.
7-pf capacitor.
b. 7-uh inductor.
d.
350-pf capacitor.
8. The circuit shown in figure 43 of TM 11-668 is used to modulate a 40-MHz
oscillator.
Assume that, with no audio signal applied, this circuit injects an
inductance of 7.6 uh into the oscillatory circuit. If LL = 0.4 mh and RL = 15K, a
tube must be selected that has a transconductance of approximately
a. 1,500 micromhos.
c.
7,000 micromhos.
b. 3,500 micromhos.
d.
9,000 micromhos.
9. Assume that each of the four RC sections of the oscillator in C of figure 48,
TM 11-668, has a phase shift of 45 at 4 kHz. When the resistance of the variable
resistance leg (modulator tube) is increased, the phase shift for that section is
reduced to 30 and the output frequency is lowered. To retain the 180 total phase
shift, the phase shift in each of the other RC circuits is now
a. 30.
50.
c.
b. 45.
60.
d.
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