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

[Mark Haun]

On Mon, 20 Jan 2020 15:25:00 -0500
Bob kb8tq <kb8tq at n1k.org> wrote:
> On Jan 20, 2020, at 2:57 PM, Mark Haun <mark at hau.nz> wrote:
> > Agree except you were starting from the VFOV numbers for the 100-MHz
> > version.  If you use their numbers for the 10-MHz version and add
> > 20 dB for an ideal 10x multiplication, for comparing with the ABLNO
> > spec at 100 MHz, you end up with
> > 
> > offset    VFOV405 @ 10M, ideal 10x multiply     ABLNO @ 100 M
> > 10        -100                                  -88
> > 100       -120                                  -118
> > 1k        -140                                  -141
> > 10k       -145                                  -160
> > 100k      -145                                  -161  
> 
> If indeed -145 is “good enough” then you have moved out of the “good
> phase noise” region into fairly generic sort of specs. A “couple of
> dollar” oscillator will give you -145 sort of noise floors. 

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.

Hypothetically, sure, any old 80-MHz OCXO with "generic" phase-noise
performance would suffice.  But hobbyists can't just pick up the phone
and order something like that; we're limited to surplus/used stock,
where 80-ish MHz is unusual.  And of course most surplus/used OCXOs
would require high voltage (5V or above), high power (half a watt or
more), or both.

Sorry, I didn't plan to expound on my design rationale at such length,
but you seemed curious :)  

Regards,
Mark