[time-nuts] Symmetricom 023-63008-07 5MHz Crystal Oscillators

[Bob kb8tq]

Hi

One interesting thing to do with good / cheap OCXO’s:

If you multiply an OCXO from 5 to 10 MHz, noise goes up by 6 db.
If you mix two independent 5 MHz OCXO’s to get 10 MHz, phase noise goes up by 3 db.

The same thing happens with ADEV, multiply has no impact. Mixing *should* only get you
sqrt(2) of the original ADEV.  ( This assumes the ADEV is not coming from a common source
like temperature …..)

Indeed you could go crazy with hundreds of OCXO’s. Practical setups might run 2, 4,  or 8
devices. If indeed they are 20 to $30 sort of parts, four get you somewhere around $100 for 
the OCXO’s. Mixers / filters / pc boards might double the total cost. 

Mixing 4 would cut the ADEV by two and drop phase noise by 6 db compared to a multiply.
If you had an ideal divider, you could indeed get 6 db better noise at the original frequency. 

Compared to chasing “unobtanium” grade OCXO’s this could get you low parts in 10^-13 without
spending years loosing out on kilo-buck level auctions. ( …. and possibly getting one that 
does not work ….).

Taking the plotted data, you might hit 2x10^-13 at 10 seconds with 4 or 8 OCXO’s. Would you
break 3x10^-13 at 1 second? Only way to know is to try it :)

Indeed, there are a variety of ways to do the combination. Each has it’s benefits ….

Bob

> On Jan 22, 2020, at 2:51 PM, cdelect at juno.com wrote:
> 
> Hi,  I'm testing some of these for a project and they have pretty good
> performance!
> 
> Attached is a plot of a very nice one.
> 
> Most are in the mid to high 10-13th Allan Deviation!
> 
> Need to cover to prevent drafts while testing for best results, I just
> lay a piece of bubble wrap over the unit on the bench. 
> 
> 800ma cold 300ma warmed up 5Mhz sine wave out SC cut with EFC input an
> +5v Ref output.
> 
> Very fast warmup!
> 
> Can be adjusted plus minus 1.5Hz, would make a nice offset oscillator for
> a DMTD (1Hz offset)
> 
> Also listed as 023-63008, eBay has some and if you Google it there are
> some direct sellers.
> 
> Does anyone know what these were removed from?
> 
> Be interesting to know as there seem to be quite a bunch out there!
> 
> Cheers,
> 
> Corby<885ad.bmp>_______________________________________________
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