[time-nuts] Ancient OCXO in scope calibrator.

Bruce Griffiths bruce.griffiths at xtra.co.nz
Tue Sep 9 18:49:59 EDT 2008


Thomas A. Frank wrote:
>> A ceramic alignment tool doesn't cause the same behaviour, but a  
>> probe sure
>> does.
>>     
>
>
> Something is whispering "grounding".
>
> I'm not sure why, but that is where I would start looking...
>
> Tom Frank, KA2CDK
>
>
>
>   
This particular variant of the miller oscillator uses the screen grid to 
grid1 capacitance for feedback.
This capacitance is at most a few pF.
Thus even a shunt capacitance as small as 1pF to ground at the grid will 
change the effective the feedback capacitance significantly.
Both the crystal and the cathode load impedance are inductive at the 
oscillation frequency.

Bruce




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