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.
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----- Original Message -----
From: "ed breya" <[email protected]>
To: <[email protected]>
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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