[time-nuts] EFC Input pin impedance for the HP 10544A and10811-6011

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sun Oct 28 22:27:32 EDT 2007

Mike Feher wrote:
> While it is difficult to read the resistor values on that schematic (and as
> Bruce points out not really relevant as the diodes are reverse biased), it
> appears that since the varicap is referenced to ground, the 10544A's EFC is
> always positive. The 10811A goes from -5 to + 5 as the cathode end of the
> diode is referenced to +6.4 volts. All this time I had thought they were
> fairly interchangeable. - Mike 
> Mike B. Feher, N4FS
> 89 Arnold Blvd.
> Howell, NJ, 07731
> 732-886-5960

Get yourself a better GIF viewer and magnify the image (all component
values can then be read), you will find there is an option to connect
the varicap cathode to +6.4V just like the 1081.
The problem only arises if one has the other option.


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