[time-nuts] 10811 Extra Lagging etc

Richard (Rick) Karlquist richard at karlquist.com
Tue Jun 20 01:03:21 EDT 2006

> 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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