[time-nuts] 10811 foam enclosure

Tom Van Baak tvb at LeapSecond.com
Sun Jan 9 23:36:50 UTC 2011

>>Q)  None of  the hp/Agilent bench test equipment that uses these 
>>oscillators uses  insulation. Perhaps that's a  clue.
> a) It is not much of a clue, considering that a patent & knowledgeable 
> time-nuter can get 10 to 100 + better performance out of them.

The spec page for the 10811A is here:

To avoid misunderstanding could you clarify which of those
specifications you can get 10 to 100+ better performance?

> Look inside a HP Z3801 GPS.

Right, that's why I wrote "bench test equipment". None of the
hp test & measurement products use insulation around the

The Z3801A is unique; that was a 1st generation telecom unit;
the only piece of hp gear with a custom heat blanket wrapped
around a stock OCXO.

The outer oven was a hack so Z3801A could meet telecom cell
tower cold weather warm-up specs. In other words, the better
performance they were looking for in that case was warm-up
time; not a tempco or frequency stability spec.

The external blanket is reminiscent of the 115 VAC fast warmup
heater in the vintage 00105 brick oscillators (a predecessor of
the 10544 and 10811).

But unlike the 00105 the Z3801A reportedly uses PID control on
the blanket. For that reason I would expect that the outer shell
could improve the tempco of the oscillator, but I haven't seen
data on that. Does anyone have actual measurements? A long
run with, and without, the outer oven circuit connected would
tell the story nicely.


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