[time-nuts] Spec An for phase noise measurements

[David I. Emery]

On Mon, Jan 21, 2008 at 01:18:15PM -0800, Matt Ettus wrote:
> On Jan 21, 2008 12:41 PM, John Miles <jmiles at pop.net> wrote:
> >
> > > John,
> > >
> > > I'm a little confused as to what you are suggesting.  An 8662A is
> > > about $1500, and the 11729C is about $3k.  What would I get for $25?
> >
> > The parts needed to implement Wenzel's app note:
> > http://www.wenzel.com/documents/measuringphasenoise.htm
> >
> > > I don't know exactly what is involved with the 11729 and how it makes
> > > measurements.
> >
> > Take an hour and look through this HP app note (large file, but only about
> > 50 pages):
> > http://www.thegleam.com/ke5fx/gpib/5952-8286E.pdf
> >
> > It is not all that specific to the 11729B/C despite making frequent
> > references to it.
> 
> Makes sense now.  One problem -- the 8596E only goes down to 9kHz, at
> least according to the specs.

	Spectrum analyzer front ends often either have a blocking
capacitor (to protect the mixer from DC) or don't.    The kind that
don't usually start to roll off pretty significantly below 10 KHz, and
are typically spec'd only to 9 KHz.   I suppose if one wants to live
REALLY dangerously the cap  might be removable in a few cases (NOT
RECOMMENDED)....
	
	But would I be too simple minded to suggest that maybe some form
of A/D PC/workstation input device with high dynamic range and decent
sample rate (certainly available in high end audio stuff to 192 KHz)
would be the logical vehicle for close in measurement in a quadrature
locked PLL type phase noise setup ?   Otherwise why would you care about
performance below 9 KHz ?

	Why exactly does one need a wideband SA that goes down to 100 Hz
(common spec) or 30 Hz (nicer and newer...) for this ?   Maybe I am missing
something here.... (probably am, I often do...)

	And should one want an actual SA for these measurements instead
of a soundcardish thing and FFT software, I know that LF/HF boxes with
better specs than any of the affordable general coverage SA families on
Ebay show up regularly for not too much money.

> 
> Matt
> 
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-- 
  Dave Emery N1PRE/AE, die at dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."