Hi With these little OCXO’s you likely will move them 0.1 ppb simply walking past the bench. If they have a total of 0.25 ppm of trim, a 25 turn pot will get you 1 ppb per turn. Setting these pots to 1/10 turn is not all that crazy.
Yes, there are a bunch of assumptions made there and your setup may or may not behave quite like the one I have described. Bob > On Dec 24, 2017, at 11:32 AM, John Ackermann N8UR <j...@febo.com> wrote: > > I didn't really notice much backlash, though when setting oscillators I try > to approach (slowly) from one direction until it's "good enough" and then > stop, to avoid that problem. > > On Dec 24, 2017, 11:28 AM, at 11:28 AM, Dana Whitlow <k8yumdoo...@gmail.com> > wrote: >> John, >> >> Do you notice a backlash effect when homing in on the desired setting >> with >> those >> tripots? I last used such things back in the 1980's, and remember >> often >> having >> enough backlash to make close trimming rather difficult. >> >> I wonder if they have gotten better in that regard. >> >> Dana >> >> On Sun, Dec 24, 2017 at 9:58 AM, John Ackermann N8UR <j...@febo.com> >> wrote: >> >>> I'm glad that the PulsePuppy post spawned some good discussion! >>> >>> The pot I'm using is a Bournes 3296W-1-103LF which is a 25-turn, 10K, >>> cermet pot, spec'd at 100ppm/degree, so it's not anything super >> fancy. The >>> number of turns provides decent setability, and it seems to be a good >> match >>> for the class of oscillator the PulsePuppy is designed for -- I found >> that >>> I could trim the Isotemp oscillator without problems. >>> >>> I'll admit up front that the PulsePuppy wasn't designed as a host for >>> ultra-stable oscillators. I tried to keep the circuit board size and >> cost >>> down, as well as the number of components that users would have to >>> install. And since the EFC trimmer is one of those user-installed >> parts, >>> it's possible to substitute as nice a pot as you'd like. I have one >> unit >>> that's hooked up to an external precision pot with a turn-counter >> dial >>> (just because it was there). >>> >>> John >>> ---- >>> >>> On 12/24/2017 03:57 AM, Mark Goldberg wrote: >>> >>>> Can you specify what pot you have used? I am using some for my TCXO >> boards >>>> and am not quite happy with the settability or mechanical stability. >>>> resulting in noise and higher Allan Deviation. >>>> >>>> A low noise regulator driving it also helped. >>>> >>>> I subscribe to the opinion to not use any extra resistors. When the >> pot is >>>> used as a voltage divider, theoretically it should have the same TC >>>> throughout, so temperature effects should not affect the divide >> ratio or >>>> the output. Only the input impedance of the control voltage input to >> the >>>> oscillator relative to the effective resistance of the pot will >> provide >>>> some effect with temperature. >>>> >>>> Mark >>>> _______________________________________________ >>>> time-nuts mailing list -- time-nuts@febo.com >>>> To unsubscribe, go to https://www.febo.com/cgi-bin/m >>>> ailman/listinfo/time-nuts >>>> and follow the instructions there. >>>> >>>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to https://www.febo.com/cgi-bin/m >>> ailman/listinfo/time-nuts >>> and follow the instructions there. >>> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.