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

[Bob kb8tq]

Hi

I think you will find that some fairly generic oscillators will hit the “more or 
less 1x10^-10” sort of spec needed for HF com work. A good OCXO will get
you into the 1x10^-12 range. The limit generally is the “floor” imposed by 
propagation variance at HF. 

Bob

> On Jan 20, 2020, at 3:50 PM, Mark Haun <mark at hau.nz> wrote:
> 
> 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
> 
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