[time-nuts] getting a grip on 10811 drift (trying to read my instruments)

[Graham / KE9H]

Chris:

This says your EFC circuit is not working, and you are only
getting 0.05 Hz frequency change across the -5 to +5 EFC range.
The spec on the HP10811 is 1.0 Hz minimum.

And, yes, in a counter the  EFC circuit is not used, so no one would
know if it failed.

It is very simple circuit.  The only active component is a
varactor that the EFC voltage is applied to.

There was a very recent thread about someone else that
had to replace that varactor in a HP10811 and what he
used.

Search for thread titled "HP 10811 Tuning Diode."
 From the period October 18 through October 19, 2012.

--- Graham

==

On 11/15/2012 8:57 PM, Chris Howard wrote:
> You all were right, my targeting of the 50 ohm resistor
> across the oscillator output does not seem to have solved the
> problem.   A good thing to do, probably, but not the answer.
>
> While I was all excited about the resistor change I also
> mapped out the control voltage (EFC) vs frequency change.
> I wrote it out but didn't pay much attention.  Now
> I've been pondering over that a bit.  My next theory
> is that my EFC maybe isn't really doing very much.
>
> First I need to know if I am reading this right.
> My frequency counter is a Racal 1992  It reads
> 9.99999997^6   as I write.  A total of 9 digits
> with a smaller "6" to the right.
>
> If I read this correctly, I'm looking at
> 9,999,999.97  Hz ?  If so, then I've got an EFC problem.
>
> My EFC mapping looks like this (this was done before
> I adjusted the coarse control)
>
>
> -4.94 VDC         9,999,999.95
> -3.70             9,999,999.95
> -1.24             9.999.999.93
>   0 VDC		  9,999,999.93
> +1.21             9,999,999.92
> +2.44             9,999,999.92
> +3.67             9,999,999.91
> +4.90 VDC	  9,999,999.90
>
> It doesn't look to me like I am getting anything
> like 1/2 hertz range using the EFC.  If that's
> the case than my controller card is frantically
> steering but not getting the desired result.
>
> Or, if I'm reading it wrong,  maybe that last digit
> is 0-5 meaning 1/2 a hertz and I am all wet (again).
>
> This particular oscillator came out of an old HP counter
> and I believe the EFC was wired to ground.  So maybe
> the thing has never been exercised.  Are there versions
> of the 10811 that don't have EFC guts inside?
>
> Hope I'm not boring you all to death.
>
> Chris
> w0ep
>
>
>
> On 11/9/2012 11:26 PM, WarrenS wrote:
>> Chris
>>
>> HP 10811 can't drift that much that fast unless something is near broken, or being connected wrong like gnds or PS voltage.
>> Check the operation of the oven.
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