Keysight Technologies N9030B, Service Manual

Page: 227 / 617

N9030B PXA Signal Analyzer Service Guide 227
Analog/Digital IF Troubleshooting
A2 Analog IF Assembly Theory of Operation
A2 Analog IF Assembly Theory of Operation
Input Switch and Filter
A 322.5 MHz input signal is received from the A15 Front End Control
Assembly. The signal then goes through a band pass filter centered at
322.5 MHz with a 25 MHz bandwidth. A comb cal signal can be
automatically switched in at the input of the assembly to calibrate the
prefilters.
Step Attenuator and Amplifier
A 1 dB step attenuator follows to compensate for band gain differences.
The signal then goes through a high-dynamic range amplifier.
Image Filters
One of three different filter paths will be selected automatically, depending
on the analyzer mode.
— The through path is selected in IQ Analyzer Mode and wide-band
demod.
— The 12 MHz ceramic bandpass filter is used for normal Signal
Analyzer swept and FFT operation.
— The 300 kHz Surface Acoustic Wave (SAW) is used for ACP modes.
Mixer
There are two mixers that reside on this assembly. The first mixer is used to
down convert the 322.5 MHz input to the final 22.5 MHz IF. The other mixer
is described in the IF Comb Cal section.
3rd LO
The 300 MHz 3rd LO signal comes from the A16 Reference Assembly and
conditions it for use as an LO in the two mixers that reside on this assembly.
The third LO power is ~ +10 dBm to optimize the conversion efficiency of the
first mixer.
IF Comb Cal
The 2nd mixer is used to mix the 300 MHz LO from the Reference Assembly
with the 22.5 MHz cal comb signal from the A3 Digital IF to allow
calibration of the prefilters and overall passband phase and amplitude. The
signal is attenuated by 20 dB if necessary.
Refer to Chapter 13, “Block Diagrams” .