Hi There are a lot of different designs out there. What you find on eBay and in most OEM systems these days has a common ground pin for everything. The typical logic on the system designer’s end is “we only have one ground on the PC board, it’s all going there immediately”. Out of a thousand designs, you might see one or two with something fancy done on the EFC return.
Bob > On Feb 4, 2020, at 9:26 AM, Dana Whitlow <k8yumdoo...@gmail.com> wrote: > > 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. _______________________________________________ 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.