Rob, I don't think so. The WWVB receivers I have mix to baseband, not a lower IF. The image issue you note is not a problem with these receivers. If the DCF77 receivers mix to 625 Hz, they had beetter have very good image rejection. That would require a very narrow passband consistent with a crystal filter. Having said that, this has nothing to do with EMI inband susceptability at 60 kHz.
Dave Rob van der Putten wrote: > Hi there > > > David L. Mills wrote: > >> Not to get into a pissing contest, but both WWVB and the European LW >> services operate at similar frequencies and ERPs European services >> operate at higher latitudes where noise levels are lower, while WWVB >> operates at lower latitudes and generally longer ranges. I've lived in >> Europe and can attest the differences. >> >> WWVB has claimed carrier accuracy of 1e-11 and has carrier phase >> ambiguity of 16 microseconds. Electronics-wise, a narrowband crystal >> filter ahead of a phase-lock loop with a time constant of a couple >> minutes pins the zero crossings well below one microsecond. While the >> modulation bandwidth is quite narrow, finding the right on-time cycle >> crossing with 5 ms risetime (30 cycles) and a comb filter isn't hard. >> Thats how the WWV audio demodulator works. >> >> The Spectracom WWVB radios we have used to do an excellent job; >> however, the claimed accuracy was only 0.1 ms, mostly because the >> computer used for demodulation was so chintzy. Sadly, WWVB is dead >> here because of EMI generated by hundres of UPS systems all over >> campus. I'd be curious to know if this has also affected DCF-77 users. > > > AFAIK DCF-77 runs at 77.5 kHz and a lot of receivers mix this down to > 625 Hz; This means a mirror at 76.875 kHz. Interference sources will > therefore be at 38.75 and 38.44 kHz (2nd harmonic). > Switching stuff often runs at 25, 30 or 33 kHz. So a frequency of 60 kHz > (WWVB) will have more interference. > > > Regards, > Rob _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
