[time-nuts] EFC tracking
jmiles at pop.net
Sat Jun 26 22:25:28 UTC 2010
> >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
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
> 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
More information about the time-nuts