Hi I guess I assumed that we were talking about a modern GPSDO like the Thunderbolt - my bad.
Indeed, if you have a messy PPS then you need to first generate a clean one. Bob On Nov 13, 2010, at 2:37 PM, Magnus Danielson wrote: > On 11/13/2010 08:12 PM, Bob Camp wrote: >> Hi >> >> Ok, so right now you are looking at about 10 degrees out of 360 where one >> cycle is 100 ns. More or less you are in the 3 ns range. >> >> Some cheap stuff that will do better: >> >> HP 5334 >> HP 5335 >> HP 5345 >> HP 5370 >> HP 5371 >> >> All are in the "sub $300" range on the normal sites. Some are sub $100. All >> are available with GPIB for logging. >> >> For a bit more money >> >> HP 53131 >> SR 620 >> >> You may find one for sub $1000. Often you see them listed for nutty prices. >> I certainly would not pay anywhere near $1,000 for either one. >> >> The one I'd go for is the 5334. It's smaller than the rest. They likely are >> the cheapest of the group. The ones I have *seem* to be more reliable than >> some of the rest of the stuff listed. >> >> All of them can run in any one of three modes: >> >> 1) PPS to PPS timing >> 2) PPS to 10 MHz edge timing >> 3) 10 MHz to 10 MHz timing > > Technicality - you want to have a stable rate of measurements. One way to > achieve this is to use a PPS or similar trigger. The TADD-2 divide-down kit > can be handy to proivde triggers from a 5 MHz or 10 MHz source. > > In particular you would enjoy triggering the measurement from a PPS (or > divided down 10 MHz to say 10 Hz or 100 Hz) and then do Time Interval > measurements with one 10 MHz rising edge (say reference) to the other 10 MHz > rising edge. I have had great success with this method myself. > >> Number 2 on the list seems to have the fewest issues. > > Actually, depending on the GPSDO style the PPS may be the "raw" GPS PPS or > the smoothed variant being a divide down from the 10 MHz. Method 2 would not > be as clean as you would wish for some GPSDOs. Using the trigger variant > described above is preferred since it would would have less issues with the > noise of the PPS relative to the 10 MHz. > >> A completely different approach: >> >> Pump both signals into a phase detector (RPD-1 or X-OR or what ever) >> and use a DVM to log the voltage. You can get some super overkill >> DVM's for less than you can get any of the counters. They will >> easily get you into the sub ns range on resolution. Weather the >> setup will be accurate at this or that level is in the "that depends" >> category. > > Hmm. Gotta try that one. > > Cheers, > Magnus > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
