[time-nuts] OCXO aging behavior

Alan Melia alan.melia at btinternet.com
Wed Sep 2 15:06:07 UTC 2009

Maybe this is not "aging" you are looking at...parts in 10^9 over a few days
sems a bit high for that (??) on a good quality crystal but I think you may
find that is around the spec for the reference in the 1992. I never bother
setting my (older Racals) counter to better than 1in 10^9 its good enough
for the workshop, but I do measure them now and again and record the offset.

Alan G3NYK
----- Original Message -----
From: "John Green" <wpxs472 at gmail.com>
To: <time-nuts at febo.com>
Sent: Wednesday, September 02, 2009 2:58 PM
Subject: [time-nuts] OCXO aging behavior

> I had always thought that crystals changed frequency consistently in one
> direction as they age. That is until recently. I was trying to get the
> reference in my 1992 as close as possible to my Z3801 and noticed that as
> adjusted the fine pot, there didn't seem to be a place where the frequency
> stayed put. It seemed to drift lower over a days time. So, I thought I
> set it a little high and over the weekend it would go lower and closer to
> the Z3801. Much to my surprise, I found it had gone even higher over the
> weekend. I gave up on trying to get it so close and settled for around
> or so. I am going to watch it over a few weeks to see what happens next. I
> have also noticed something like hysteresis in frequency adjustment. A
> little tweak in one direction can only be offset by a larger tweak in the
> opposite direction. I assume all this is normal. I just had not been able
> see it until I started using a GPSDO to compare things to. After hearing
> much about how sensitive Tbolts are to temperature and antenna location, I
> am going to feed both the Z3801 and a Tbolt off the same antenna and see
> I can see any differences. I don't know if I have the equipment for it,
> it should be interesting.
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