78 Chapter 2
Performance Verification Tests
10. Residual FM
10. Residual FM
This test measures the inherent short-term instability of the analyzer
LO system. With the analyzer in zero span, a stable signal is applied to
the input and slope detected on the linear portion of the IF bandwidth
filter skirt. Any instability in the LO transfers to the IF signal in the
mixing process. The test determines the slope of the IF filter in Hz/dB
and then measures the signal amplitude variation caused by the
residual FM. Multiplying these two values yields the residual FM in
Hz.
For instruments having Option 1DR (Narrow Bandwidths), since the 10
Hz resolution bandwidth filter is digitally implemented, its slope is well
known. The measured amplitude variation is simply multiplied by the
known slope to yield the residual FM in a 10 Hz resolution bandwidth.
There are no related adjustment procedures for this performance test.
Equipment Required
Synthesized signal generator
Cable, Type-N, 152-cm (60-in)
Additional Equipment for 75 Ω Input
Pad, minimum loss
Adapter, Type-N (f), to BNC (m), 75 Ω
Additional Equipment for Option BAB
Adapter, Type-N (f), to APC 3.5 (f)
Figure 2-10 Residual FM Test Setup