Aliasing (if that is indeed what's going on) can be a problem with any digital sampling device, including your 'scope. 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.
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.