[time-nuts] Spec An for phase noise measurements

Matt Ettus boyscout at gmail.com
Mon Jan 21 15:13:04 EST 2008

On Jan 21, 2008 11:44 AM, John Miles <jmiles at pop.net> wrote:
> After working with a quadrature PLL/LNA, I feel very strongly that anyone
> who's serious about PN measurement should go this route.  I wasted a lot of
> time myself, sitting around wishing I could afford a quieter spectrum
> analyzer.  It's simply the wrong question to ask.
> It's true that the HP 8590s are among the noisiest spectrum analyzers out
> there, but the difference between the phase-noise floors of an 8596E and an
> 8560E is only about 20-25 dB.  The difference in cost is several thousand
> dollars.  If you invest in a nice 8662A instead -- or even an 8640B! -- you
> can use your *existing* 8596E to make measurements 30-40 dB below what even
> the 8560E series can do.
> This is a seriously-nice thing to be able to do at home.  You can use a
> quadrature PLL to do things like compare different crystal-oscillator
> circuits and look at DDS phase-noise floors... and lots of other things you
> would never be able to do with a spectrum analyzer alone.
> I'll see if the list will let me attach a small .GIF showing the difference.
> The 11729C's noise floor is about 6-10 dB below the green trace, which is a
> comparison of a couple of decent-quality 100 MHz OCXOs.  Note how much
> higher the direct measurement floors of your current spectrum analyzer and
> an 8560E are.  For $25 in parts, you could make the measurement in the green
> trace with your 8596E!  Spend the extra money on signal generators, and/or
> collecting VCXO references at various frequencies.


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?
I don't know exactly what is involved with the 11729 and how it makes

If I just connected a quadrature PLL and LNA, I would still need a
very clean VCO at the same frequency, right?


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