> Aliasing (if that is indeed what's going on) can be a problem with any > digital sampling device, including your 'scope.
Not quite aliasing, I think, but close. > You may find the "peak > detect" function in the "acquire" menu useful. I assume your TDS1002 has > one as my TDS2024 does. Also, perhaps the "holdoff" function might > improve your triggering stability. I can only conveniently trigger off the LORAN pulse which is gated RF with no set or stable relation between the RF carrier phase and the gating pulse. -John ================ > On Jun 6, 2011, at 12:40, J. Forster wrote: > >> As some of you know, I've been working on restoring a WW II LORAN-A >> system. To test it, I've been using a Tektronix TDS1002 Digital 'Scope >> and >> a Military TS-251 Test Set. >> >> First a bit about the LORAN-A signal. It is a precisely timed Master >> pulse >> of roughly 2 MHz RF. The spacing of the Master Pulse is precisely >> crystal >> controlled, but the RF is just gated... the carrier is not locked to >> the >> Master Pulse. It looks sort of like this: >> >> >> |||||....................................|||||................. >> >> ^ >> | Master Pulse start. >> >> Anyway, I was triggering on the Master Pulse and looking at several >> succeeding ones, all generated by a TS-251 Test Set. >> >> For the longest time, I could not figure out why the successive Master >> Pulses envelopes were bouncing around all over the place by perhaps a >> factor of 5. >> >> Eventually, I worked out that most of the samples taken by the digital >> scope were being taken during the quiet time, and the actual LORAN pulse >> was being badly undersampled. This resulted in displayed waveform that >> had >> almost nothing to do with what the system was really doing. Also, >> because >> of slight trigger uncertainties, the LORAN pulse was being "smeared" in >> time. >> >> IMO, the lesson is that digital scopes do not always accurately depict >> what a circuit is doing. Even a $50 analog 'scope would never have this >> issue. >> >> FWIW, >> >> -John >> >> =================== >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > .73, > Brent, KD0GLS, Minneapolis > > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.