Don't "good" OCXOs float the oven stuff and use a separate return pin instead of a GND pin common with the OSC GND pin?
Dana On Tue, Feb 4, 2020 at 7:42 AM Bob kb8tq <kb...@n1k.org> wrote: > Hi > > The great thing about a wire wound pot is that as a voltage divider, it has > a very low temperature coefficient. The problem with adding resistors is > that their temperature coefficient will not match that of the winding > material > on the pot. The “value” of the wire wound is lost in this case. You might > as well > just run a multi turn cermet pot. > > One alternative are the big multi dial voltage dividers you see from time > to time > on eBay. Prices (as with anything on eBay) are all over the map. Score > some > cheap and you can get a lot of resolution and a lot of stability. > > Another alternative would be to grab some “zero drift” op amps. Buffer up > a pair of > pots and then drive a thin film network with them. (or spend around $20 > each on some > shiny new low TC resistors). Then buffer the sum junction with another > op-amp. > > =========== > > If the oscillators are OCXO’s, ground current is going to make problems > pretty > quickly. With a common ground pin and voltage changes measured in > millivolts, > it limits how well a normal OCXO can be set. > > Bob > > > On Feb 4, 2020, at 2:18 AM, Perry Sandeen via time-nuts < > time-nuts@lists.febo.com> wrote: > > > > Learned Gentlemen, > > Thanks for the two references for affordable 10 turn precision pots. > > This will allow me to go back to my original and simpler circuit of a > series string of resistors and in that string connecting the 10K10 turn pot > in parallel with one of the resistors, probably a 1K, which will be set by > the upper slightly above and the lower just below the *sweet spot* needed. > It will take a bit of juggling for each oscillator but that will be far > simpler than using 3 digital pots. > > Regards, > > Perrier > > _______________________________________________ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
