[time-nuts] Possible HP 10811 instability clue

[Richard (Rick) Karlquist]

Regardless of isolated anecdotal data on one oscillator, it
is probably not advisable to change the set point. The majority
of 10811 crystals do NOT have a turnover, only a region of
low tempco around 82 degrees.

Instead of that, change the circuit to B-mode and optimize
the heat between the two heater resistors for maximum thermal
gain (you should be able to get 1000).  Then change the circuit back to 
normal.

Rick Karlquist N6RK


On 10/6/2010 6:59 PM, Perry Sandeen wrote:
> Gents,
>
> Some on this list mentioned having had less-than-optimal performance with their HP 10811 series oscillators.  James Miller G3RUH made a slight mention of optimizing performance by readjusting the set point temperature in one of his phase detector articles.  He said though time consuming the results were worth the effort.
>
> Looking at the schematic it shows that a thermistor was used in a bridge circuit.  The final set point was obtained by using a selected resistor from the HP chart.  The value went from 1.33K for 80.0 C to 34 ohms for 83.8 C.
>
> Although HP probably selected the best thermistor possible they drift over time.  Also complicating the issue is that the drift is non-linear. At that time the only other choice for an accurate non-drifting sensor was a platinum 100 ohm sensor.  While highly accurate the rate of change per degree is very, very low which would require complicated amplification.  Because of the platinum sensor cost and the associated circuitry that choice would have been cost prohibitive.
>
> I suppose if it were designed somewhat more recently some sort of SS sensor would have been used.
>
> I don’t know how James Miller did his turning point process but perhaps this might point someone in the right direction.
>
> Regards,
>
> Perrier
>
>
>
>
>
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