[time-nuts] Frequency referenced temperature regulator

[Garry Thorp]

But since I happen to have access to much more stable frequencies than voltages, I thought of a different way:

1. Mount a X-tal-osc with really lousy tempco inside the enclosure

2. Compare its output to a stable reference frequency.

3. Use the output of the phase comparator to drive the Peltier.

It is basically a PLL where temperature is used as EFC..

 
SC-cut crystals have a linear (but I don't know how linear!) negative TC in the B-mode. A quick search didn't throw up much literature on the subject.
 
I recently tried 2 separate 100MHz 5th-overtone crystals (same spec, different batches) in the same oscillator, tuned for the B-mode. The frequency change from +25 to +85°C appeared to be well within 1% for the 2 crystals, with a mean TC of ~ -27.8ppm/deg C. I didn't dwell long enough at intermediate temperatures to check the linearity accurately, but they looked quite linear at first sight.
 
If you have an OCXO surplus to requirements, with an SC-cut crystal, you could try tuning it to oscillate in the B-mode (typically ~ 9-10% high), disconnect the heater and calibrate its frequency against temperature. (Of course you will need a calibrated oven to do this.......)
 
Garry
Pascall Electronics Ltd - Registered in England No: 1316674 VAT Registration No: GB 448705134 Registered Office: Brunswick Road, Cobbs Wood, Ashford, Kent, TN23 1EH

The transfer of any controlled technology contained in or attached to this email is covered by the "Open General Export Licence (Technology for Military Goods)", granted by the United Kingdom Secretary of State. GBOGE2008/01354

The information contained in this email is provided as a personal communication of the sender and, as such, is not binding on Pascall Electronics Ltd. unless the intended recipient has been notified by signed postal or fax communication that the sender is authorised to commit Pascall Electronics Ltd. on the subject matter concerned.The contents of this email are confidential to the intended recipient at the email address to which it has been addressed. It may not be disclosed to or used by anyone other than this addressee, nor may it be copied in any way. If received in error, please contact Oli Poole, at opoole at pascall.co.uk, quoting the name of the sender and the addressee and then delete it from your system.