[time-nuts] My Racal-Dana 1992

Charles P. Steinmetz charles_steinmetz at lavabit.com
Tue Dec 20 01:51:55 EST 2011


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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