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

[Bob kb8tq]

Hi

If you do try it, double balanced mixers seem like the way to go. 

Two 5’s into one mixer gives you 10, a low level spur at 5 and some crud at DC. 
Duplicate that with another mixer and you have a second 10. Maybe go into a 
low Q filter to clean it up a little. Since you have loss in the mixers you will need
some gain. At this point you have 4 OCXO’s running. 

Drive those into another mixer and get 20, 15, 10, 5 and DC crud. Hopefully the
15,10, and 5 are pretty far down. You will need a filter at this point. Again some 
sort of low Q tank likely does a pretty good job.

Duplicate that whole setup and you have a second 20 MHz. Same mix / filter / gain
process gets you 40 MHz. You now are up to 8 OCXO’s.

Do it one more time and you are at 80 MHz with 16 OCXO’s. With a (potential) spur 
at 75 and 85 MHz, the filtering involved may be a bit more involved. 

Divide down to 5 or 10 with who knows what and away you go.

So what are the issues?

1) You do need gain and it needs to be clean enough not to mess up the ADEV. 
That gets a bit harder the closer you get to 80 MHz. It should be doable without
going to crazy.

2) You can’t have any of the OCXO’s injection lock with each other. That may take
some effort. I’d arbitrarily tune each one this or that way to reduce the risk. There 
might be a gotcha doing that. 

3) As noted in another thread, DBM’s like to generate odd order nonsense. That
is not to say they generate *no* even order distortion, only that it is lower. You 
may get into a low level spur problem (2X F in). I’m guessing it will be far enough
down to not be a problem. It is one limit the tuning in 2 above. 

4) If you keep the tuning process simple and feed EFC into only one OCXO, the 
tune range goes down 16:1. With a wide tune OCXO that may not be a big deal.
Offset tuning them all to accomplish 2 above would also be possible but a bit 
exciting to implement. 

One “interesting” thing to try:

Phase lock an 80 MHz VCXO to the 80 MHz output with a good low noise analog
PLL setup. If you are just after ADEV, this might be a better way to nuke the
spurs than a crazy filter. 

Bob





> On Jan 23, 2020, at 12:06 PM, cdelect at juno.com wrote:
> 
> Bob,
> 
> I just might play at the mixing to see if it will work!
> 
> Hmmm, 16 oscillators give a cold current of  12.8 Amps!
> 
> The direct sellers you find with Google sell them for <$20.00 each.
> 
> One of them:
> 
> https://www.teewtfstore.com/index.php?main_page=product_info&products_id=
> 244548
> 
> This seller (can't quite figure out where they are located) Seems to
> indicate Canadian dollars?
> 
> If you buy 4 or more at $13.16 CA shipping is free.
> 
> Cheers,
> 
> Corby
> 
> 
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