Common IF Signature Problems
n Region A of Figure 8-4 is noisy: Suspect the first LC pole.
n Region B of Figure 8-4 is flat: Suspect the third step-gain stage, the fine attenuator, or the
fourth LC-pole output amplifier.
H
Region C of Figure 8-4 has no 15 dB step: Suspect the reference 15 dB attenuator.
n Region D of Figure 8-4 is flat: Suspect the second step-gain stage.
n Entire signature noisy: If the signature resembles Figure 8-9, 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.
n Correct shape but noisy: If the signature resembles Figure 8-10, suspect the second
crystal-pole output amplifier.
n Amplitude of Region B of Figure 8-11 varies more than 12
dB:
Suspect the third step-gain
stage output amplifier.
n Region B of Figure 8-12 is kinked: Suspect the fourth LC-pole output amplifier.
REF 10.0
dBm
ATTEN
20
dB
I
I I I
I
I
5
dB,’
SAMPLE
CENTER
10 700
SPAN 0 Hz
RES BW 300
kHz
VBW 300
kHz
SWP 500
set
SK178
Figure 8-9. Noisy Signature
8-28 IF Section
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