[time-nuts] Timing between two GPS PPS outputs.

[Dan Kemppainen]

Hi all,

I've been following this list with some interest, and have a question 
about two individual timing GPS units PPS outputs. Let's assume that 
the timing GPS units are identical units, say two SSR-6t's for example.

If I take these two units and fire them up next to each other off of 
the same antenna one would expect the PPS signals to be very similar 
to each other. If the unit specifies 20nS, I would expect at most, 
say, 40nS Error between the two PPS signals. (Maybe this is not 
correct, by all means discussion is welcome).

Now, lets say we fire these units up on different antennas at the same 
location. For the purpose of this discussion let's assume the antennas 
are identical or as identical as reasonably possible. (Same make, 
mode, cable length, etc). Will they still be within the specified 
errors or each other?

Now, lets say we move them some distance apart say 500meters (or yards 
if you prefer). Do they still maintain the same relative error between 
them?

The reason for this question is two fold.  I have a personal project 
in mind where I'd like to time stamp two events within several tens of 
hundreds of nS if possible, over some distance without cabling. Also, 
as I started thinking of this application, I realized my understanding 
of the details of GPS timing is a little weak. I figured this would be 
a good place to ask.

Thanks,
Dan