19. b--Attached Memorandum, para 5-4a, fig.
5-2
Sketch 3 in figure 5-2 shows a signal generator being used for signal
substitution.
For checkpoints 1 through 5, the signal generator is set for an
audio frequency (400 Hz).
As the output of the generator is applied to each
checkpoint, if the circuits are good a tone is heard in the speaker.
When
checkpoint 5 produces a tone, you know that the audio stages are good.
Now the
generator must be set to produce a modulated IF (455 kHz). This signal is applied
to the checkpoints starting at number 7 and working toward the mixer.
If the
trouble is in the RF stage, you will hear a tone from all checkpoints through the
output of the mixer. Now set the generator for an unmodulated RF (1,000 kHz) and
apply the signal to the RF input of the mixer. If a tone is heard you know that
the oscillator is good. Your trouble must be located between the antenna and the
RF input of the mixer.
You have set the signal generator to three different
frequencies.
20. d--Attached Memorandum, para 5-3, 5-4c
322 S
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