[time-nuts] LP filter on EFC line

[Bruce Griffiths]

Richard Moore wrote:
> Bruce, thanks for the tip on the anti-charge injection LP filter.  
> Actually, early on, I put a 0.1uF cap across the EFC line on the osc,  
> support board, so there is some LP filtering working there. But my  
> old Tektronix "prayer wheel" Circuit Computer says that's only a 5ms  
> TC -- prolly need quite a bit more or else buffer the EFC line from  
> the DPM.
>
> Best,
> Dick Moore
>
>
> On Oct 31, 2008, at 5:56 PM, time-nuts-request at febo.com wrote:
>
>   
Dick

Something like 1K, 10k, 100K in series with the Hi lead and 1nF, 10nF or
100nF to ground at the DPM end of the resistor.
With a floating DPM also need 1k, 10K, 100K series resistor with 10nF,
100nF or even 1uF to ground at the DPM end of the resistor.

Exact values and time constants required depend on the DPM and circuit
characteristics.
You will need to do the experiments to find out which combinations work
best.

Even with a buffer an output low pass RC filter will help.

Bruce