[time-nuts] New Question on HP3048A Phase Noise Test Set

[BriMDavis at aol.com]

Martyn wrote:
>
>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!!!
>
 
 To make sure I understand your results, here's how I would 
summarize your measurements, inserting some made-up numbers 
for observed spur and noise floor levels:
 
 RF analyzer directly measuring 10 MHz signal :
 
   - spur at 10.000100 Hz is @ -50 dBc
 

3048A L(f) measuring coherently demodulated phase:
 
   - spur at 100 hz is @ -56 dBc
 
   - noise floor is -160 dBc/Hz at 5 MHz offset
 

3048A Sphi(f) measuring coherently demodulated phase:
 
   - spur at 100 hz is @ -53 dB
 
   - noise floor is -157 dB/Hz at 5 MHz offset
 

If this is what you are seeing for relative changes in level
for the different measurements, I think the 3048A is working 
just fine.
 
Here's another experiment to try [1]:
 
 - change spur to an offset of 500 kHz @ -50 dBm
this moves the spur into broadband analyzer territory
 
 - re-run your L(f) and S(f) plots at this offset 
I would expect the same 6 dB, 3dB spur results for L(f), S(f)
 
 - change the measurement setup BW to zero Hz instead of 1 Hz,
and measure Sphi(f) again
 
      This forces the 3048A to NOT apply bandwidth corrections
to the collected data, so it will display a segmented-looking 
trace with increasing floor offset across each band break
 
      
Brian
 
[1] It's been about 7 years since I've actually pushed the buttons 
on a 3048A, so my recollection of setup and S/W behavior might 
be a bit fuzzy




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