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 > > > _______________________________________________ > time-nuts mailing list > [email protected] > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
