With a scope it is super easy to look at PPS pulses that are microsecond to a few milliseconds wide and tell you are triggering on the "leading edge".
Harder to decide at 50% duty cycle especially if you think it might have been inverted along the way (almost all buffers are inverting). Of course if you were 50% duty cycle you could figure out which edge was which by listening to WWV. Oops not that topic again. Tim N3QE On Tue, Aug 14, 2018 at 2:52 PM, Bernd Neubig <[email protected]> wrote: > Another question, a bit off the road of this thread: > Is there any common practice for the duty cycle of the 1 PPS pulse? > I have seen devices having extremely short 1 PPS pulses with duty cycles > of a few percent or less and others with close to 50% duty cycle. > > Best regards > Bernd > DK1AG > > -----Ursprüngliche Nachricht----- > Von: time-nuts [mailto:[email protected]] Im Auftrag von > Bob kb8tq > Gesendet: Dienstag, 14. August 2018 17:05 > An: Discussion of precise time and frequency measurement < > [email protected]> > Betreff: Re: [time-nuts] 1PPS for the beginner > > Hi > > > > On Aug 14, 2018, at 10:33 AM, Ron Bean <[email protected]> > wrote: > > > >> A normal GPS module generates it \200\231s outputs off of a free > >> running internal clock. Generally this is a TCXO in a > >> \200\234timing \200\235 GPS ( = one that puts out a rational PPS). > >> This i bit counter intuitive, since you would *think* they phase lock > >> the local source in the module. They don \200\231t mainly because it > >> makes the math easier. > > > > Is there a need to make the math easier? > > This is what we have microprocessors for. > > There is *always* a need to make the math easier if I’m quickly typing up > an example. For proof I reference the hundreds of posts in the archives > where I didn’t quite get it right :) > > Indeed, the real numbers could be just about anything. They are highly > dependent on what’s in the specific module. In some cases, the clock > involved is well over 300 MHz. > > Bob > > > > > Thanks for the "hanging bridge" explanation. It would be nice if > > someone had a time-nuts-glossary that included various terms that come > > up on the list, like "hanging bridge", "spurs", "sawtooth correction", > > "GPS allan ski jump", etc. > > > > Is there a time-nuts FAQ? > > > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] To unsubscribe, go > > to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- [email protected] To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to http://lists.febo.com/mailman/ > listinfo/time-nuts_lists.febo.com > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
