[time-nuts] My Racal-Dana 1992

Don Latham djl at montana.com
Tue Dec 20 14:31:40 EST 2011

Ah. That seems right, Charles, going by the behavior. In that case, what
and where is the reference for the heater servo? The ambient
temperature? Not too wise a choice, but what else? So it may be that the
temperature is the controlling element but it, too, is an open system?
It can be open, too, just second order?
This is a knotty one!
Charles P. Steinmetz
> Don wrote:
>>This is typical for an underdamped second order servo. The oscillation
>>is the penalty for a shorter settling time. A critically damped system
>>would not oscillate, but approach the final value smoothly in a
>> slightly
>>longer time. It may have been designed for a slight overshoot...
> Yes, I understand and I don't doubt that it is performing as
> designed.  My point was that most crystal oscillator frequency
> adjustments (at least, the ones that I have seen) are open-loop
> (variable capacitor or pot to a varactor diode).  Finding the fine
> frequency control apparently in a servo loop was a surprise.  And it
> cannot be a PLL or FLL, because there is only the one reference --
> the one you are adjusting.  Since the startup dynamics are so similar
> to the fine frequency adjustment dynamics (not to mention that the
> oven loop is pretty much the only possible servo in the oscillator),
> the evidence appears strong that the fine frequency adjustment is an
> oven temperature adjustment.  Unless there is something truly
> diabolical going on inside a 9462.
> Best regards,
> Charles
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"Neither the voice of authority nor the weight of reason and argument
are as significant as experiment, for thence comes quiet to the mind."
R. Bacon
"If you don't know what it is, don't poke it."
Ghost in the Shell

Dr. Don Latham AJ7LL
Six Mile Systems LLP
17850 Six Mile Road
POB 134
Huson, MT, 59846
VOX 406-626-4304

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