2Nd If Amplifier; 2Nd If Filter; Step Attenuator; 3Rd Lo - Keysight N9000A Service Manual

nd
2 IF Amplifier
Provides IF gain and isolation between the second mixers and the 322.5MHz
bandpass filter.
nd
2 IF Filter
Provides image filtering (~25MHZ BW) when in wide-band demod mode, and
protects downstream circuits from strong out-of-band signals.

Step Attenuator

A 1 dB step attenuator follows to compensate for band gain differences.
rd
3 LO
The 300 MHz 3rd LO signal comes from the A9 L.O. Assembly and conditions it
for use as an LO in the third mixer that reside on this assembly.
rd
3 IF Amplifier
First amplifier
Provides fixed gain (about 13dB) to improve noise figure.
Second amplifier (variable amplifier)
Provides variable gain to keep overall gain constant for different paths.
Step Gain amplifier (last amplifier)
Provides an additional switchable 10 dB of gain to overcome the ADC noise floor
and provide an additional 2 dB or so of sensitivity.
rd
3 IF Filter
The third IF filters are anti-alias filters, which attenuate unwanted out-of-band
noise and distortion products. The first anti-alias filter is centered at 22.5 MHz
with 25 MHz wide. The signal can bypass the second anti-alias filter when the
analyzer utilizes Basic Analyzer swept, or wide-band demod. The through path is
selected when the image filter is in the 25 MHz mode (for Basic Analyzer swept
and wide-band demod). In all other cases the signal will pass through the second
12 MHz anti-alias filter.

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.
Chapter 4
RF Section Troubleshooting
RF Section Theory of Operation
129