[Discuss-gnuradio] Using DSP for precise zero crossing measurement?

[John Ackermann N8UR]

I wonder if there is someone on the list who'd be willing to let me call 
them on the phone to talk about the feasibility of using DSP techniques 
(i.e., GnuRadio) to very precisely measure the zero crossing point of a 
slowly changing waveform with some noise on it.

More precisely, the goal is to measure the zero crossings of a pair of 1 
Hertz sine waves, having an amplitude of perhaps 1 volt peak to peak, 
with a precision of ideally 100 nanoseconds.  We want to determine the 
true zero crossing point, somehow eliminating the effect of any noise on 
the signal.

The zero crossings are then used to calculate the time interval (or 
phase) between the two waves.  I need to capture each pair of zero 
crossings, and can't average over multiple intervals.

The challenge of doing this with conventional techniques like a time 
interval counter is that trigger jitter becomes a huge problem with a 2 
volt/second slew rate.  I'm hoping that DSP techniques might provide a 
way around this problem.

It might be easier to explain further details over the phone, so if 
someone is interested in guiding me through this problem, please let me 
know and I can get your number off-list.

Thanks!

John