Phase Noise Troubleshooting

If the Phase Noise test fails, check the results of the DANL TEST. If DANL is out of spec, there is a good possibility that the high average noise-level is causing the noise sidebands test to indicate a false failure.

Phase Noise is a parameter that describes short term instability of LO tune frequency. Phase Noise appears as modulation sidebands near the LO. The modulation source is noise within the LO Phase Lock Loop.

A Phase Noise failure would indicate that noise is being injected into the LO Phase Lock Loop. The assembly most likely to be the source of the failure would be the A14 L.O. Synthesizer Assembly.

Failures at the 100 Hz offset are usually caused by AC line related (100 Hz/120 Hz) spurs. If a distribution amplifier is being used to distribute the analyzer 10 MHz to multiple sources, remove it from the path. Distribution amplifiers tend to add AC power related spurts to the reference signal.

Another, but least likely, assembly that could cause a Phase Noise failure would be the A13 Front End Assembly.