[time-nuts] Re: Which GPSDO for an accurate, low phase noise 10 MHz?

[Greg Maxwell]

For radio I use a PRS10 (/SRS725) that is conditioned on its 1PPS input by
a gps timing receiver-- though I'm not currently doing anything as high as
10GHz, and its phase noise ( http://www.ke5fx.com/rb.htm ) probably gets
beat by your 10811A... if all you really need is signal to adjust your
OCXOs then the phase noise performance ought not matter (so long as it
isn't completely awful), and your x72 or any timing receiver PPS ought to
be enough to serve that purpose.

For a while PRS10 could easily be extracted from various bits of kit that
showed up on ebay, though I'm not sure if that's still true.

> but with one brand the phase noise was so bad, one couldn't make out the
primary tone on the spectrum analyzer

I think that's likely the fault of the particular transverter.  If you
multiplying an oscillator up to 10GHz then that is going to be very
sensitive and it really needs a good cleanup oscillator.






On Tue, Apr 29, 2025 at 4:03 AM Bill Katz via time-nuts <
time-nuts at lists.febo.com> wrote:

> Hello.
> I found this group last year when I was working on my microwave rover
> station (up to 10GHz currently, 24 GHz soon) when I ran into a challenge.
>
> First I bought a small Rubidium standard, hoping that would keep my system
> accurate. (Symmetricom x72 from ebay).  It looked fine with some
> transverters, but with one brand the phase noise was so bad, one couldn't
> make out the primary tone on the spectrum analyzer.  The next step was a
> club member sent me an HP 10811A, which has great phase noise, but showed
> some drift when I fed my counter from the rubidium standard.
>
> Oh, and once I repaired the (apparently somewhat common) temperature fuse
> inside the second 10811A inside the counter, I now had two oscillators that
> almost agree.  Almost.
>
> So I'd like to get something that can run the instruments in my house, and
> allow me to calibrate the OCXO in my rover equipment.  And tweak in the
> various other OCXO standards.
>
> At the high end, there are used HP Z3801As that seem to have excellent
> phase noise, but are somewhat expensive.  At about half the price are used
> Thunderbolt units.  and there are a myriad of other options.  What are the
> pros/cons of some of these units?
>
> Thank you,
> Bill Katz
> KA1TZ
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