Chapter 8 441
IF Section
A5 IF Assembly
Common IF Signature Problems
Region A of Figure 8-4 on page 436 is noisy:
Suspect the first LC pole.
Region B of Figure 8-4 on page 436 is flat:
Suspect the third step-gain stage, the fine attenuator, or the fourth
LC-pole output amplifier.
Region C of Figure 8-4, “Detailed IF Adjust Signature (1),” has
no 15 dB step:
Suspect the reference 15 dB attenuator.
Region D of Figure 8-4 on page 436 is flat:
Suspect the second step-gain stage.
Entire signature noisy:
If the signature resembles Figure 8-9 on page 442, suspect a broken
first step-gain stage or a break in the signal path in the input switch,
first crystal pole, or second crystal pole.
Correct shape but noisy:
If the signature resembles Figure 8-10 on page 443, suspect the second
crystal-pole output amplifier.
Amplitude of Region B of Figure 8-11 on page 444 varies more
than 12 dB:
Suspect the third step-gain stage output amplifier.
Region B of Figure 8-12 on page 445 is kinked:
Suspect the fourth LC-pole output amplifier.
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