198 Keysight NFA Series Noise Figure Analyzers Service Guide
RF Section Troubleshooting (N8973B, 74B, 75B Analyzers)
Troubleshooting
High Band Preamp (Standard Option P07, P26)
The High Band preamp can be verified as follows:
View the 4.8 GHz calibrator signal on screen. Press AMPTD, Signal Path,
Internal Preamp, Full Range 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 and 13.6 GHz to 17 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
N = 2 for 13.5 GHz to 17 GHz
For input signal frequencies above 8.4 GHz to 13.6 GHz and 17 GHz to
26.5 GHz:
RF = LO x 2 x N − IF
IF = LO x 2 x N − RF
LO x 2 x N = IF + RF
where RF is the input signal at the signal analyzer
where N is the harmonic mixing mode:
N = 1 for 8.4 GHz to 13.6 GHz
N = 2 for 17 GHz to 26.5 GHz
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