Erik and Larry thanks for your suggestions.
I connected CH0 on the Nanovna to a scope, and at first it was difficult to see any difference in the signal, especially since the signal has a periodic "DC blip" at the end of the sweep. I switched the Nanovna to CW freq, and triggered after the blip, and was able to get a steady waveform. Now, I could see a difference in waveforms when the CW freq was set to 99.9MHz or 100MHz. At 99.99MHz the waveform is steady, but at 100MHz it seems that there is jitter in both the amplitude and phase. I also connected CH0 to a spectrum analyzer, and noted a broadening of the spectrum when operating at 100MHz.
I tried running clearconfig, and recalibrating, but there was no change in results.
I guess I have a problem with the test signal generation. Erik, would you recommend replacing the Si5351?
