Hi If you wire up all the possible circuits and check them all out … the answer is that big C / small R wins. Big R gets you into resistor noise issues and stray pickup.
Bob > On Aug 1, 2016, at 4:16 PM, David <davidwh...@gmail.com> wrote: > > This duplicates the problems encountered when trying to quantify low > frequency noise from a voltage reference; it is difficult to make an > low frequency high pass filter with lower noise than the lowest noise > references and the capacitor is the problem. > > In Linear Technology Application Note 124, Jim Williams discusses the > problems with electrolytic capacitors for this type of application. I > have read that you *can* get away with aluminum electrolytics if you > grade them for low leakage and low noise. The dielectric absorption > is also a problem unless you can wait hours for best performance. > > What about the alternative of buffering the signal with a low noise > low input bias current operational amplifier so that a large film > capacitor can be used instead? Is the low frequency noise of a good > operational amplifier still too much? What about a chopper stabilized > amplifier without suitable output filter? > > On Mon, 1 Aug 2016 11:46:51 -0400, you wrote: > >> Hi >> >> > .. until you discover that you picked the *wrong* capacitor manufacturer and > you have >> more noise from leakage in the cap than you did to start out with :) In >> general big C and >> small R is the better solution than big R and small C. >> >> The pesky part is that with electrolytic caps, the whole noise current >> thing changes as >> the voltage moves around. You go to measure things and by the time the gear >> is set up, >> the noise has dropped. Turn it all off, come back the next day and its >> noisy again. >> >> An even more subtle issue can be capacitor temperature coefficient on really >> long Tau filters. If C >> changes (due to temperature fluxuations) faster than the settling time of >> the filter, you get noise. Charge >> is the same so delta C gives delta V. >> >> I *wish* I could tell you that was all purely theoretical. Unfortunately >> its based on empirical data >> collected in the how could I be so stupid fashion. >> >> Bob >> >>> On Aug 1, 2016, at 11:21 AM, KA2WEU--- via time-nuts <time-nuts@febo.com> >>> wrote: >>> >>> A good filter in the cable is highly recommended, 5 KOhm & 1000 uF cleans >>> many things > _______________________________________________ > 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.