> Le 22 déc. 2015 à 06:16, Brian Inglis <[email protected]> a > écrit : > > On 2015-12-21 18:24, [email protected] wrote: >> So I've been playing with some timing hardware here, and have noticed >> something rather curious. I have two otherwise identical Lea-6T GPS modules, >> configured exactly the same. These units are tied to the same antenna, with >> a splitter with the same length cables running to each unit. They were given >> the same survey coordinates. Initially there was not any appreciable >> difference between the PPS outputs. The outputs were on average within about >> one nS of each other. However after a day or two they started to display a >> difference of about 21nS between the PPS outputs. This is also evident in >> the GPSDO output, as the phase of the 10Mhz is also skewed by 21nS or so. >> >> A few days ago I started a 48 hour survey. The came up virtually identical >> coordinates at the end of that survey. After the survey the phase is still >> 21nS different. >> >> At this point, my only thought is the GPS splitter. It's DC coupled to one >> unit, and AC coupled to the other. It is possible there are some delays on >> one output vs. the other due to the blocking caps and bypass inductor in the >> splitter. I've tried swapping the GPSDO units on the splitter, so we'll see >> what happens there. >> Can anyone offer any insight as to why the two units may have a different >> PPS output timing? It's not really a problem, more of a curiosity and mildly >> academic exercise. > > A sampling difference of 1 cycle with 48Mhz clocks would give you ~21ns > offset if not using sawtooth correction. Can you do the sawtooth correction > and see if the offset is reduced? >
Good thinking Brian. But I would expect the difference to wander from 21s UNLESS the the two receivers clocks are lock stepping. Injection locking might do this if the two module are physically close enough. > -- > Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada > _______________________________________________ > 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. "The main function of a modern police force is filling in forms." _______________________________________________ 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.
