CHAPTER 5
THEORY
The rf output developed in this stage is fed to the first
40. Introduction
doubler stage.
This chapter contains a description of the
b. First Double. First doubler V6 amplifies and
r
description provides an understanding of each stage and
doubles the frequency of the oscillator output signal. Its
aids troubleshooting and repair.
output signal voltage at a frequency between 47.5 to
100 mc is applied to rf amplifier rT.
41. Description of Operation
c. Rf Amplifier This stage amplifies the signal
.
Signal Generator SG-3/U is shown in the block
output of the first doubler without changing the
diagram (fig. 8). A brief description of each stage
frequency of the 47.5- to 100-mc input signal. The
shown is contained in the paragraphs which follow. For
output of the rf amplifier is applied to the FREQ.
more detailed overall circuit information, refer to the
RANGE-MC selector switch and to the second doubler
complete schematic of Signal Generator SG-3/U (fig.
stage. When the FREQ. RANGE
44).
Figure 8. Signal Generator SG-3/U, block diagram.
output of the rf amplifier serves as the signal generator
a. Rf Oscillato. Rf oscillator V5 is a modified
r
output signal.
Colpitts oscillator with a range of 23.75 to 50 mc. The
fundamental oscillator frequency is determined by a
d. Second Doubler. The output signal from the
setting of the manually operated TUNING control.
first doubler is amplified by V7 and then the frequency is
When the signal generator is used to provide an fm
doubled by second doubler V8. The output frequency of
signal, a saturable reactor, which is part of the oscillator
this stage (95.0 to 200 mc) is four times the fundamental
tank circuit, frequency-modulates the oscillator output
oscillator frequency.
signal. MC switch is in the 50-100 mc position, the
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