[time-nuts] Odd-order multiplication of CMOS-output OCXO

[Mark Haun]

Hi Attila,

On Mon, 20 Jan 2020 14:29:15 +0100
Attila Kinali <attila at kinali.ch> wrote:
> On Mon, 20 Jan 2020 11:13:46 +0100
> Attila Kinali <attila at kinali.ch> wrote:
> 
> > With those constraints, and reading the discussion, I wonder why
> > don't consider a VCXO+PLL solution. Using something like the
> > Abracon ABLNO and a generic PLL (e.g. ADF4001) would give you above
> > performance. The ABLNO are so low noise enough, that you can use a
> > low BW loop filter (order of 500Hz) and get lower output noise than
> > the up-multiplied 16MHz signal above that and the (multiplied) OCXO
> > performance below that (with a slight bump due to the PLL around
> > the loop filter frequency).  
> 
> Addendum: I don't know your application, but in a general high-speed
> sampling systems, it's the white noise floor that you are worried
> about, not the 1/f^a noise. And in that case, having a lown noise XO
> produce your sampling clock is better than multiplying a low frequency
> OCXO and using this directly, even if the XO is free running.

A fair question... in fact I was initially planning to use the ABLNO +
a PLL.  The OCXOs I found, however, are CTS VFOV405's with phase noise
claimed to be just as good as the ABLNO or CVHD VCXOs:
https://www.ctscorp.com/wp-content/uploads/VFOV405.pdf
They are reasonably low power, small[-ish], and have adequate stability
for my needs.  You can see why it is tempting to make the multiplier
scheme work, as it should save on both power and board area. (The
target application is a battery-powered SDR.)  So far there don't seem
to be any show-stopper issues with the plan, except that I am going to
have to put together a phase-noise measurement system, or find a friend
with one.

To that end, I wonder if something like Andrew Holme's project,
http://www.aholme.co.uk/PhaseNoise/Main.htm
is the best "bang for the buck" right now?  It looks like that could be
put together for well under $1k (minus the Wenzel ULN oscillator :).  A
simpler, sound-card-based approach is also appealing, but I have not
seen any ready-to-build projects published on the web, and I cannot
afford to put in the hundreds of hours it would take to design my own.

Regards,
Mark