10. Residual FM, HP 8591EM

This performance veri￿cation test must be performed with the EMC analyzer set in the spectrum analyzer mode.

This test measures the inherent short-term instability of the EMC 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 ￿lter skirt. Any instability in the LO transfers to the IF signal in the mixing process. The test determines the slope of the IF ￿lter in hertz per decibel (Hz/dB) and then measures the signal amplitude variation caused by the residual FM. Multiplying these two values yields the residual FM in hertz. The narrow bandwidth

test uses a 300 Hz span. This span is not speci￿ed, however, it is tested in \Frequency Span Accuracy."

There are no related adjustment procedures for this performance test.

Equipment Required

Signal generator

Cable, Type N, 183 cm (72 in)

Figure 2-13. Residual FM Test Setup, HP 8591EM

Procedure

This performance test consists of two parts:

Part 1: Residual FM

Part 2: Narrow Bandwidth Residual FM

2-44 Performance Veri￿cation Tests