used with IN270 diodes employed for detection.
The
audio
output
from
the
discriminator appears across audio gain control R9.
4-13.
AUDIO AND SQUELCH CIRCUITS
The audio signal is fed from the volume control through a 0.02-microfarad
capacitor to the base of transistor Q13, which is directly coupled to the audio
output stage Q14. The collector of Q14 feeds the transducer horn or the earphone
at an impedance of 600 ohms.
Squelch is provided through noise amplifier Q11,
rectifiers CR4 and CR5, and dc amplifier Q12.
The squelch is activated when the
volume control is first turned on.
Switch S2 grounds the squelch circuitry to
deactivate the squelch voltage when the volume control reaches the maximum point on
its rotation.
The squelch threshold control, R8, is an internal adjustment and
normally will not require changing unless a change in receiver characteristics
occurs.
4-14.
POWER CIRCUIT
Power for this receiver is supplied by a 6-volt battery through switch S1.
Silicon diode CR6 furnishes the bias for audio stage Q14.
Inductors L2, L3, L4,
L5, L6, L9, and L10 isolate the individual stages.
LESSON EXERCISES
In each of the following exercises, select the ONE answer that BEST completes
the statement or answers the question.
Indicate your solution by circling the
letter opposite the correct answers in the subcourse booklet.
1. Squelch circuits are often incorporated in FM receivers to remove background
noise during the time that a signal is not being received.
A limiter-derived
voltage can be used to provide a reduction of background noise by applying the
voltage to the
a. discriminator through a squelch tube.
b. audio amplifier through a squelch tube.
c. audio amplifier grid as a negative bias.
d. discriminator plates as a negative bias.
2. The voltage to operate a squelch tube is usually derived from another part of
the receiver. The stages that may be used to supply the voltages include the
a. rectifier and local oscillator.
b. dc amplifier and discriminator.
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