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 -- Lifestyle sux _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
