[time-nuts] How do time-nuts measure phase noise?

John Miles jmiles at pop.net
Mon Aug 17 18:38:48 UTC 2009


The 85671A is fine, subject to the analyzer's LO noise floor.  Some
analyzers are quieter than others, but in no case can you use a spectrum
analyzer by itself to characterize crystal oscillators or other high-quality
HF sources.

I have a much nicer host-based application that does the same thing as the
85671A, runs on many different analyzers, and yields much more readable
plots (see http://www.ke5fx.com/gpib/pn.htm ).  There are also some pointers
to app notes from Wenzel and HP on quadrature test sets in the last FAQ
entry at http://www.ke5fx.com/gpib/faq.htm .

The executive summary is that quadrature test sets are not that complex.
You can save a lot of money by building your own, if you need to measure
sources beyond the reach of your spectrum analyzer alone.

That NIST box looks very nice but I have no idea what it does.  If it's just
a quadrature PLL and collection of filters, that can be done for a lot less
than $4000.  If it's got features like an ensemble of built-in reference
oscillators, then $4000 could be a bargain.

-- john, KE5FX

> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
> Behalf Of J. L. Trantham
> Sent: Monday, August 17, 2009 7:22 AM
> To: 'Discussion of precise time and frequency measurement'
> Subject: Re: [time-nuts] How do time-nuts measure phase noise?
>
>
> Can anyone provide any information on the usefulness of the Phase Noise
> Utility program (85671A) for the HP 8560 series Spectrum Analyzers?
>
> Thanks in advance,
>
> Joe
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Bruce Griffiths
> Sent: Monday, August 17, 2009 7:13 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] How do time-nuts measure phase noise?
>
>
> Some have commercial phase noise measurement systems like Symmetricoms
> 5115A, 5120A. 5125A. Some have older HP phase noise measurement
> systems like
> the 3048A etc. The rest of us have to build our own systems based around
> sound cards or surplus spectrum analysers together with the necessary
> mixers, low noise amplifiers etc.
>
> Unless your sources are very noisy you wont be able to measure their phase
> noise with just a selective voltmeter or even an RF spectrum analyser. If
> you cant build it, then you need to acquire something like the
> HP3048 or the
> NIST phase noise measurement box currently on ebay.(Item:
> 260423038423)
>
> Bruce
>





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