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.