[time-nuts] Making a HP 10811 better

WarrenS warrensjmail-one at yahoo.com
Mon Sep 19 05:57:14 UTC 2011

The test took a while, but I finally got around to testing the effect of setting a HP10811's inner oven to the xtral's EXACT turn over temperature.
Short answer is NO Help.
I did not see any improvement in freq stability with environmental temperature changes.

It did  help in reducing the small but temporary freq step caused when the oven PS voltage was changed.
The reason why changing the oven to the Exact turnover temp does not help is because there are many other things that are still temperature sensitive that far exceeded the freq change due to xtral temperature changes when  it is at it's Turnover point,  such as mechanical stress on the case and changes of the internal buffer loading. 

My method was much more accurate and repeatable than the way it was done in the existing "somewhere report".
The test consisted of bringing out the temperature bridge voltage of a sealed 10811 Oscillator thru a high value resistor so that a large external voltage could be used to make very small changes in the Oven temperature set point.
Next I adjusted the Oven temp by way of the attenuated external voltage to the bridge resistors to find the exact turn-over temperature.
Freq resolution, repeatable and turn over was within a couple parts in e-12
Frequency TC after setting the oven was still a couple parts in e-11 / deg C.

Just to be sure, I rechecked the xtral's turn-over temperature at different room temperatures.
The turn over temperature still happen at exactly the same external voltage.  That did not change, although the Freq was different, any temperature change in the oven setpoint still caused the Freq to change in the same direction, by the same amount  when the oven temperature setpoint was raised OR  lowered by the same amount.



there is a report somewhere of resetting the oven temp in a HP 10811
to exactly find the turnover temperature.
How high is this on your list of things to do to improve a HP 10811?
Does it make the double oven unnecessary?

cheers, Neville Michie

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