[time-nuts] OXCO Issues
Max Robinson
max at maxsmusicplace.com
Sat May 11 19:05:52 UTC 2013
I once designed and built an analog proportional crystal oven. What I
didn't realize was that my bench power supply had developed a fault and
wasn't regulating perfectly. When I connected it to a good power supply it
went unstable. Rather than reengineer the control loop I connected a 2 ohm
resistor in series with the power supply. All of the electronics was on the
other side of a 5 volt regulator so it wasn't effected by the voltage
variations, only the oven heater was. It has worked fine for years that
way.
Regards.
Max. K 4 O DS.
Email: max at maxsmusicplace.com
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----- Original Message -----
From: "ed breya" <eb at telight.com>
To: <time-nuts at febo.com>
Sent: Saturday, May 11, 2013 9:42 AM
Subject: Re: [time-nuts] OXCO Issues
> Why not just run it from a separate, regulated supply? Until you check it
> with solid voltage applied, you won't know for sure - maybe the OCXO is
> OK, but the oven circuit can't handle too high an impedance from the
> supply.
>
> At low frequencies, the OC part may exhibit negative resistance, making an
> oscillator under some conditions. To see how this can happen, picture the
> unit operating in static environmental conditions. After warmup, the whole
> thing should take constant power - on average - to maintain the XO
> temperature. If the supply voltage increases, the current must decrease in
> order for the power to stay the same - again, on average, over some time
> frame. This is negative resistance, which can provide power gain to form
> an oscillator.
>
> Ed
>
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