[time-nuts] 10 MHz OCXO recommendations

[Bob Camp]

Hi

Ok, let’s back off a bit.

If 0.2 ppm over a narrow range is the objective, that sounds like a TCXO application. If you really are only after the 14.4 MHz, that’s the quick / easy way to go. Everything running on 3.3V, total current may be below 10 ma. Far fewer parts involved. A lot depends on just how that spec gets interpreted.

Surplus OCXO’s are well … surplus. A significant percentage of the OCXO’s I’ve seen on the surplus marked are pulls off boards and are busted. I’ve bought quite a few from “tested / guaranteed / 100% good / perfect buy” sellers and found issues with then when you carefully test them. My conclusion is that in most cases, tested = has some sort of output. Tested may not include “does not catch fire if left on for an hour”. I’ve bought them from the same people everybody else has. 

There are a couple ways around this. The first is to buy parts that have never been on boards. You can be pretty sure that a part with long leads has not been on a board. Finding OCXO’s at 10 MHz that way is not very easy. The next approach is to buy a working device (like a GPSDO or test gear) and pull it’s OCXO. This works much better if you bought the thing 15 years ago and its not been of any use. You could buy parts brand new, you then run into the fact (been true forever) that surplus is pennies on the dollar. The final solution is the most common - buy lots of OCXO’s and sort them out / repair them yourself. 

If you are going the sort / repair route, the Morion MV-89 parts are out there in bulk and  are pretty cheap. There are no published schematics, so it’s a trace it out and debug thing to fix one. You also need to be a bit handy with something like a torch to get them open. The trick is to do it in a way you can re-seal the parts. The “Trimble” OCXO’s are not quite as common. Welded package parts are going to be a sort only thing, Popping them open and then re-welding them - not so much. 

That Jackson Labs GPSDO on eBay is sounding better and better isn’t it? 

Bob



 


> On Nov 11, 2014, at 1:05 AM, Joseph Gray <jgray at zianet.com> wrote:
> 
>> You can run at 400 KHz by dividing by 5/5 and 4/9.
> 
> True. Either will work.
> 
>> You said "0.2ppm stability".  What do you need for accuracy and/or how
> are you going to calibrate your setup?
> 
> I will initially calibrate the OXCO against my HP GPSDO. Idealy, it will
> only need checking against the GPSDO once a year. Is that asking too much
> for it to be stable over that length of time?
> 
> I could simply look up the specs for the various models that I find on
> ebay. However, I know that a lot of the stuff that is sold has been through
> the mill and may not meet spec any more. Thus my request for
> recommendations for models that someone here has actually purchased and
> tested.
> 
> Joe Gray
> W5JG
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