[time-nuts] FRK-L OK or too tired?

Brian Kirby kirbybq at bellsouth.net
Sat Sep 9 10:10:24 EDT 2006

If the unit does not have external EFC, you can bring out the existing 
potentiometer circuit to the outside world , via un-used I/O pins..  
Most are 1 kilo-ohm 10 to 20 turn trim pots.   Replace it with a low 
tempco wire wound pot and use a turns counter. 

My unit was fairly close on frequency when I received it and the pot was 
set close to 500 ohms.  I replaced it with a 0.1 percent 460 some ohms 
precision resistor, which was mounted inside the case and a 100 ohm - 10 
turn pot was put in series with it , outside of the case - this combo 
gives about +/- 1E-10 control of the frequency.

Brian - N4FMN

Marco Bruno wrote:
> At 23.31 07/09/2006, you wrote:
>> James and Brooke,
>> Thanks for the informative replies. I have done pretty much what you
>> suggested. The result is a nice sloped line in the positive direction,
>> indicating that the FRK-L Rb source is running fast at a rate of about
>> 1e-9.
>> I checked the lamp and crystal osc monitors and both are within spec.
>> The crystal mon was 5V (2-16V is the suggested range), so I adjusted it
>> up to 10V with the range adjust trimmer.
>> I don't know if an FRK-L running for 13 years is expected to be 1E-9
>> high in frequency or if the unit could use some maintenance. The
>> suggested drift of 1e-11 per month would add up to 1.5 e-9 over 13
>> years, so it may well be within spec and need some C-field adjustment.
>> Unfortunately, when it was mounted in its box, the C-field adjust hole
>> was covered up. I'll need to power it down and do some disassembly and
>> drilling to make that adjustment accessible.
>> Suggestions? Comments?
> David,
> drill an hole, turn the trimmer and zero it. It's a perfectly 
> legitimate offset,
> and since you see a straight line it's working well. Only it needs to 
> be zeroed.
> Do it after a few hours of warm up, then check it for a week and zero again.
> It will stay in the usual +/- 1E-11 per day.
> If it has the EFC option, may be that the external voltage was used to correct
> the drift, so it may have had even a smaller drift over it's life.
> Marco IK1ODO
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