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

[Neville Michie]

I have had two 10811 with EFC problems that turned out to be lack of soldering of one internal joint.
This is a large PTFE ferule with several leads including the varactor and trimmer going into it. For many 
years the leads all contacted but finally one lead developed an oxide film. A soldering iron fixed them very quickly.
The serial numbers were widely separated, so it was not an unlucky batch problem.
cheers, 
Neville Michie

On 16/11/2012, at 1:57 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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