[time-nuts] 10811 Extra Lagging etc

Rick Karlquist richard at karlquist.com
Tue Jun 20 20:52:27 EDT 2006


Yes, I did, because nobody else had, and I was curious.
We were seeing changes along the lines of parts
in 10^8, about an order of magnitude worse than tempco.  This
was for something like dry nitrogen purge all night vs 50 degrees
C, 90% humidity for an hour or two.

After these horrible tests, I decided that the E1938 would
definitely be hermetic.

Rick N6RK

wa1zms at att.net wrote:
> Rick-
>
> You've peaked my interest. Has anyone ever collected any
> data on 10811 frequency vs. humidity or dew point?
>
> -Brian, WA1ZMS
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
> Behalf Of Richard (Rick) Karlquist
> Sent: Tuesday, June 20, 2006 1:03 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] 10811 Extra Lagging etc
>
>
>> Given that HP's engineers have done such a good job with
>> the oven and oscillator design, is there anything to be gained
>> by adding extra thermal insulation (lagging)?  How much
>
> Not a good idea.  The best thing you could do to improve
> temp stability of a 10811 is to tweak the resistors that
> proportion the power between the two heater transistors.
> At some ratio, the thermal gain will peak at over 1000
> typically.  If you just take pot luck, you would be lucky
> to do 100.  You are still limited by the tempco of the
> electronics, no matter what thermal gain you achieve at
> the crystal.
>
> You should also be aware that the 10811 is fairly humidity
> sensitive, which can seem like temperature sensitivity
> if the humidity and temperature change together.
>
> The HP E1938 was a much better design in terms of environmental
> insensitivity, but that didn't help much because the
> ultimate stability was limited by crystal frequency jumps,
> which didn't seem so bad with the 10811 due to the large
> environment errors in it.  In the E1938 they stuck out like
> a sore thumb.
>
> Rick Karlquist N6RK
>
>
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