John, I've tried different level spurs from -40 to -120 dBc. From -40 dBc to -100 dBc the spur, as shown on the HP3048A, is always 6 dB lower than it really is. So if I put a -40 dBc spur in, the HP3048A says its -46 dBc.
However, when I try from -100 to -120 dBc, the spur is a bit random and at -120 dBc the HP3048A agrees with the actual spur. But I'm sure this is because I'm approaching the floor noise of the oscillators I am using. I don't have any of my ultra low noise frequency standards at the moment, but will have two made by next week. Then I'll re-do the measurements to see what happens below -100 dBc. I'll also turn off the LNA and try that. I did do a plot selecting Phase Modulation Spectral Density (dB/Hz) on the graph instead of dBc/Hz. Here the spurs were 3 dB lower!!! Thanks to everyone for the massive amount of data on this subject. Martyn G4GMH in a previous lifetime. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
