HP 8901B Operation And Calibration Manual page 266

Model 8901B
Operation
BLOCK DIAGRAM
INPUT
ATTENUATOR IF AMP
AUDIO
E l
AUDIO
PRE.OISPLAY
SWITCH
FM
Output
Block Diagram
COMMENTS
Inherent IF Component
FM OUTPUT is unsquelched and also contains a significant component at twice the IF frequency
which is greatest when operating at
a
carrier frequency of 150 kHz.
Inverted AC Output Component
Note that the sense of the ac output component (corresponding
to
the demodulated
FM)
is inverted
for carriers above 2.5 MHz.
Accuracy of Output During RF Level Measurements
When RF Level measurements (Special h c t i o n 35) are made, automatic selection of RF
input attenuation overrides any manual settings that might have been selected with Special Function
1. The selected attenuation could degrade the accuracy
of
measurements made on the
FM
OUTPUT
signal.
3-164 FM Output