[time-nuts] Thermistor on OCXO

Azelio Boriani azelio.boriani at screen.it
Wed Oct 17 18:55:59 EDT 2012


Yes, usually increasing temperature increases frequency, so if you see an
oven current increase then slightly take down the EFC (and the other way
around if the current decreases).

On Thu, Oct 18, 2012 at 12:47 AM, Rick Karlquist <richard at karlquist.com>wrote:

> Bill Dailey wrote:
> > If I wanted to try to compensate for temperature variation of my OCXO...
> > where would I attach a thermistor?  What would be a good method of
> > attachment to best respresent the OCXO temp without opening the OCXO and
> > without an undue influence of ambient temperature?  The OCXO in question
> > is
> > Datum 1111C... was thinking of using thermal epoxy to hold it down and
> > then
> > putting some insulating material (suggestions) on top of it.
> >
> >
> >
> > --
> > Doc
> >
> > Bill Dailey
> > KXØO
>
> Probably easier to monitor oven current and use it to tweak the
> set point of the oven or tweak the EFC line of the oscillator.
> As I explained in my 1997 FCS paper on zero gradient ovens,
> the gradient is the main thing limiting thermal gain.  If you
> have a serious gradient problem, then locating the thermistor
> far away from the crystal (probably much farther away than the
> internal one) isn't likely to be productive.
>
> The other issue to be aware of is that at some point, the
> tempco of the electronics comes in play, as explained in my
> 1997 FCS paper on bridge stabilized oscillators.  Increasing
> the thermal gain of the 10811 beyond 1,000 doesn't improve
> the tempco because of oscillator circuit pulling.  You could
> possibly improve the tempco by using oven current to tweak
> the set point.  This might cancel out circuit pulling drift,
> regardless of what was going on with the crystal.  I've never
> actually tried this, but it would be good research project
> well within the ability of any time nut.
>
> Rick Karlquist N6RK
>
>
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