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

[Attila Kinali]

On Mon, 20 Jan 2020 12:50:09 -0800
Mark Haun <mark at hau.nz> wrote:

> True enough, but remember that my motivation for using the OCXO in the
> first place was to combine the required phase-noise spec with
> OCXO-class frequency stability (this is for narrowband coherent
> modulation schemes on the shortwave bands where short-term stability of
> ~ 10^-10 is nice to have).  The alternative is what Attila said,
> VCXO phase locked to an OCXO.  The advantage of doing it this way is
> that I [potentially] reduce complexity, board space, and power.

For an SDR application, the ABLNO allone would be the best option, IMHO.
It's low power and low noise. Even for narrowband SW applications.
If you look at the data, you see that the cross-over between the
ABLNO is lower noise to the OCXO is lower noise is around 100Hz.
Unless you are operating at much lower than 100baud, the ABLNO
is going to be enough. If you are using something like AFSK31/PSK31
it's probably borderline which one is better and I would go with
the ABLNO only for simpler construction and easier sourcing.

If you are thinking about trpoposcatter, EME or similar things
with really low baud rates, then I would go for the VCXO+PLL
approach for one simple reason: Flexibility. With a PLL you
have a choice what kind of reference you want to use. 
E.g. converting the system to use a MV86 would be just a different
footprint and different register settings for the PLL.

And then there ia third way, which is IMHO even better:
Your application is an SDR system, i.e. you already need some
signal processing for the system to work. Why not extend this
to use it for the reference as well? Add another ADC and feed
the reference signal to that, then track the phase/frequency
relation between the sampling clock and the reference and
compensate any drift in the signal path. This way you get to
disable the reference if it is not needed and save a lot of power
and at the same time are able to use references with any frequency
and can change the "loop frequency" freely without the need to
worry about PLL stability or tempco of filters in the multiplier
version.


			Attila Kinali
-- 
<JaberWorky>	The bad part of Zurich is where the degenerates
                throw DARK chocolate at you.