[time-nuts] Improving the stability of crystal oscillators

[John Franke]

This is something I have thought about but never did any experimentation. 
With the low cost and increased availability of thermoelectric coolers, I am 
interested in pursuing this concept.  The unfortunate thing is that the 
crystals are ground for 25C or the higher turnover temperature point.  If 
someone has a crystal that has drifted, it may be a good candidate for 
experimentation.  Another thought would be to let the crystal operate at its 
natural frequency, divide it down to 1 or ten Hz and then phase lock a more 
convenient crystal frequency to the low pulse rate.  The idea is to save an 
otherwise aged and well performing crystal.

John  WA4WDL

----- Original Message ----- 
From: "Tom Van Baak" <tvb at LeapSecond.com>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Monday, October 15, 2007 10:12 PM
Subject: Re: [time-nuts] Improving the stability of crystal oscillators


> As far as I can tell, temperature curve plots for quartz typically
> show both an upper and a lower turnover point (for example,
> see the pages below). Since the upper is well above maximum
> ambient, it makes sense that this point is used in O[ven]CXO.
>
> The question is -- does anyone know if the lower turnover point
> (LTP) is ever used? I ask because I heard that a quartz oscillator
> might have slightly better short-term stability at the LTP compared
> to the UTP. If so, this might argue for the extra trouble of using
> TEC for cooling in some low-noise applications.
>
> /tvb
>
> http://www.ieee-uffc.org/freqcontrol/tutorials/vig3/vig3_files/slide0164.htm
> http://www.ieee-uffc.org/freqcontrol/tutorials/vig3/vig3_files/slide0306.htm
>
>
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