[time-nuts] time-nuts Digest, Vol 42, Issue 39

Martyn Smith martyn at ptsyst.com
Fri Jan 18 07:57:46 EST 2008


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.


G4GMH in a previous lifetime.

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