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

Mike Feher mfeher at eozinc.com
Sun Oct 28 22:17:13 EDT 2007

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

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Bruce Griffiths
Sent: Sunday, October 28, 2007 9:53 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] EFC Input pin impedance for the HP 10544A

); SAEximRunCond expanded to false
Errors-To: time-nuts-bounces+mfeher=eozinc.com at febo.com RETRY

xaos wrote:
> Hello everyone,
> Does anyone know the input resistance of the EFC pin for the
> HP  10544A and 10811-6011 OCXO's?
> I have the spec sheet but it is not listed.
> Can I assume something like 50K? This the the value for Crystek devices.
> -George

Look at schematic for 10544A:


As long as the varicap is reverse biased only the dc load on the EFC
input is diode leakage.


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