462 Chapter9
IF Section
A5 IF Assembly
Common IF Signature Problems
Region A of Figure 9-9, “Detailed IF Adjust Signature (1)” is
noisy:
Suspect the first LC pole.
Region B of Figure 9-9 on page 459 is flat:
Suspect the third step-gain stage, the fine attenuator, or the fourth
LC-pole output amplifier.
Region C of Figure 9-9, “Detailed IF Adjust Signature (1)” has
no 15 dB step:
Suspect the reference 15 dB attenuator.
Region D of Figure 9-9 on page 459 is flat:
Suspect the second step-gain stage.
Entire signature noisy:
If the signature resembles Figure 9-14 on page 463, 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 9-15, “Noise with Correct Shape”
suspect the second crystal-pole output amplifier.
Amplitude of Region B of Figure 9-16, “Region B Amplitude
Variation” varies more than 12 dB:
Suspect the third step-gain stage output amplifier.
Region B of Figure 9-17, “Region B Amplitude Offset” is kinked:
Suspect the fourth LC-pole output amplifier.
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