[time-nuts] OCXO Retrace

[Charles Steinmetz]

Bob wrote:

>I'll see if I can figure out which of these is retracing the "wrong" 
>way and put it in a unit.  I'll let it cook for a couple of days and 
>then post a plot.  Like I said, these are all Trimble 34310-T, 
>though I know that there were at least two manufacturers for that 
>part number.  They were all positive EFC devices with more or less 
>the same frequency range.

I would expect all OCXOs with the same part number to have the same 
type of crystal (though maybe not from the same manufacturer), so 
they should all be the same (within some distribution around nominal) 
WRT the *warmup* drift.  As to the actual (post-warmup) *retrace* 
drift, there is no right or wrong direction.  If you let an OCXO go 
cold 100 times, wait a day or more (each time), and then power it up, 
it will likely retrace up sometimes and down other times.  One of my 
10811s pretty much alternates from one cold start to the next (but I 
very rarely power it down).

Once again, crystals are very individual devices with very individual 
personalities, and they are often unpredictable.  They are made to be 
powered up and left undisturbed for months/years/decades.  Use them 
that way, evaluate them that way, and don't waste time puzzling about 
what they do for the first month after you power them up.  It does 
not make any sense to power them on and off "rapidly" (off for less 
than a week, on for less than a week) and try to draw conclusions 
about anything that matters with respect to their performance.

Best regards,

Charles