[time-nuts] Couple of questions for Racal 1992 owners

[Lux, Jim (337C)]

> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Ed Palmer
> Sent: Thursday, August 27, 2009 12:06 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Couple of questions for Racal 1992 owners
> 
> Thanks for the info Antonio.  Racal didn't spec the warmup
> characteristics of the counter as a whole and it seemed a little odd
> that the warmup drift for the counter was as large as 10 days of
> oscillator drift.
> 
> Ed

Intuitively, this wouldn't surprise me.  You set the OCXO up so that the temperature is somewhat higher than the highest expected ambient (so, say, it's at 60C) and pick a crystal that has a flat freq/temp characteristic near there.  So, when you turn on, your crystal is at, say, 25C, where the slope of the freq/temp curve is pretty steep.  I'll bet someone has some curves out there that could give a quick order of magnitude estimate...

I have a poor quality chart here that shows an AT cut with about 40 ppm change for a 50 degree C change, and an SC changes about 5 ppm over the same span.  Since a decent oscillator has aging of small ppm/year, that's orders of magnitude bigger for the temperature effect.

Is this a SC or an AT cut?