252 Keysight NFA Series Noise Figure Analyzers Service Guide
Analog/Digital IF Troubleshooting
25 MHz BW IF Section
Anti-Alias Filter and Final Amplifier
The anti-alias filters attenuate unwanted out-of-band noise and distortion
products. The first anti-alias filter is centered at 22.5 MHz and is 25 MHz
wide.
The signal can bypass the second anti-alias filter when the analyzer utilizes
either the IQ Analyzer swept, or wide-band demod.
The through path is selected when the image filter is in the 25 MHz mode
(for IQ Analyzer swept and wide-band demod)
In all other cases the signal will pass through the second 12 MHz anti-alias
filter.
The step gain block provides an additional switchable 10 dB gain to
overcome the ADC noise floor and provide an additional 2 dB of analyzer
sensitivity.
Burst Carrier Trigger
The Burst Carrier Trigger detector provides a binary signal to be used as a
trigger based on the presence of an RF input signal or not. The variable gain
amplifiers drive a detector and its output drives a comparator which
generates the trigger signal.
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