Keysight NFA Series Noise Figure Analyzers Service Guide 227
RF Section Troubleshooting (N8976B)
Troubleshooting
The LO input at A13J4, and the LO outputs were tested when performing the
First LO Verification.
High Band Preamp (Standard Option P07, P26, P44)
The High Band preamp can be verified as follows:
View the 4.8 GHz calibrator signal on screen. Press MODE/MEAS, Spectrum
Analyzer, OK, AMPTD, Signal Path, Internal Preamp, Full Range, On to
activate the preamp.The expected operation is the signal level will not change
more than +/- 0.5 dB and the noise floor will increase due to the fact the input
attenuation was automatically increased.
If the amplitude error when switching the preamp on and off is greater than
0.5 dB, assure that any other internal alignment failures are resolved since the
System Gain alignment must run before optimum performance is possible. The
amplitude error could be caused by poor frequency response, and performing
the high band frequency response adjustment (using the calibration software)
will adjust the preamp on, high band path. Assure you have evaluated all
causes including A15 Front End Controller switching problems, before you
replace the Front End assembly.
High Band Mixing Equations
For input signal frequencies from 3.6 GHz to 8.4 GHz:
RF = LO x N − IF
IF = LO x N − RF
LO x N = IF + RF
where RF is the input signal at the signal analyzer
where N is the harmonic mixing mode:
N = 1 for 3.5 GHz to 8.4 GHz
For input signal frequencies above 8.4 GHz to 44 GHz:
RF = LO x 2 x N − IF
IF = LO x 2 x N − RF
LO x 2 x N = RF + IF
where RF is the input signal at the signal analyzer
where N is the harmonic mixing mode:
N = 1 for 8.4 GHz to 17.1 GHz
N = 2 for 17.1 GHz to 34.0 GHz
N = 4 for 34.0 GHz to 44 GHz
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