> >sound card ADCs, the high end 24 bit ones, are pretty darn linear [...] > > That is actually a very debatable proposition, a lot of them are > tracking types that conveniently cover up any lack of linearity > on the analog side of the fence.
Can you elaborate on that? Linearity is linearity - wouldn't it ultimately show up in the card's IMD specs? > The major problem with using sound ADC's is that their references > has absolutely no long term stability, so you will see your EFC > wiggle and wander all over the place, even when it stays perfectly > still. One idea: the sound card gives you at least two input channels to work with, and it isn't much of a stretch to assume they share a common reference. Perhaps you could use one channel to digitize the oscillator's supply voltage or (ideally) EFC reference voltage output, using the same chopper/mixer/VFC/whatever approach, and have the software take the difference out. > I would find one of those cheap-ish DVM's with a serial or USB port... I'd be surprised if a cheap DVM outperformed a decent sound-card ADC in any respect, other than perhaps DC baseline drift. -- john, KE5FX _______________________________________________ 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.