John, Just read your excellent reply after I had pressed the button to send mine which covered the same points, though much less eloquently, many thanks.
73 David Anderson GM4JJJ > On 29 Nov 2014, at 08:39, John Marvin <[email protected]> wrote: > > There's some wrong information being propagated here. Somehow the failure of > frequency comparators and/or frequency standards that were based on doing a > PLL with the CARRIER of the WWVB signal is being extrapolated to the failure > of all Radio Controlled Clocks which do not track the carrier but instead > read the time code that is imposed on that carrier. This is completely wrong. > > The new Phase Modulation signal is imposed on top of the legacy PWM signal > that has been broadcast pretty much since the beginning. Radio Controlled > Clocks that just read the PWM encoding should not be affected by the phase > changes of the PM signal, and will still work as before. The reason that some > clocks may only get a lock at night is purely an issue of propagation, and > will almost certainly be true for clocks located in the eastern part of the > US. In fact, that is the primary reason for adding the PM signal, since it > can be decoded at lower signal strengths than the PWM signal can be decoded. > > However, devices like the HP-117 and Spectracom 8170 performed a PLL on the > carrier of the signal, since the carrier frequency itself is very accurate. > These are broken by the addition of the PM signal, since it is flipping the > phase of the signal by 180 degrees periodically. None of the cheap consumer > "Atomic Clocks" do this (phase lock the carrier). People have developed > external circuits that "reclock" the WWVB signal and allow these type of > devices to continue to work. > > Also, WWVB did shut off the PM part of the signal for a few hours every night > during a transition period that ended in May 2013. That is no longer > happening, but again this only affects phase locking receivers. Specifically > LaCrosse states clearly on their website that their clocks are not affected > by the addition of the PM signal. > > Finally, I don't think there any commercially available clocks, at least at > the consumer level, that support the new PM signal at this time. The decoder > is patented, and I believe chips that support it are either still in > development or only recently released. I'll try to do some more research > regarding this. > > Regards, > > John > AC0ZG > >> On 11/28/2014 1:18 PM, Ken G Kopp wrote: >> I have a long-time close friend who's retired from >> the NBS in Boulder and was the project engineer >> on the NBS #7 cesium standard. After the recent >> reflector postings about WWV / WWVB I thought >> I would get first-hand recent information from him. >> >> The GPS satellites all carry on-board cesium >> standards that are synchronized with NTIS, and >> because of changes (below) to WWVB, cell phones >> remain the most accurate source of time for most of us. >> >> All the HF transmitters at Ft. Collins are the same TMC >> units that were put in service when the facility was built. >> The 2.5 and 20 MHz transmitters run at lower power due >> to propagation considerations. >> >> The time and other station-related voice info is sourced >> on site in Ft. Collins, and the various propagation and >> weather info comes from various "dial in" land-line >> sources. Hence the widely varying quality of these >> announcements. I forgot to ask about the individual >> who made the voice recordings ... >> >> Here's the most important info .... as of about a year >> ago the modulation scheme on WWVB (60 kHz) was >> changed (phase reversal each minute) and this has >> rendered most of the end-user equipment inoperative. >> Most (all ?) tracking receivers like the HP-117's are >> now useless without extensive modification. >> >> Most of the "atomic" clocks now in use ->do not<- synch >> to the current modulation scheme on the 60 kHz signal. >> This will explain the differences in displayed time on >> supposedly identical clocks and how some appear to >> not be getting sufficient enough signal to synchronize. >> >> He offered no comment on how to locate "consumer" >> clocks that -do- respond to the "new" modulation scheme. >> >> The 60 kHz transmitter is indeed an ex-LORAN C unit, >> and because of the higher power of the "new" transmitter >> the antenna system was rebuilt using material from the >> LORAN C site. >> >> The 20 kHz transmitter was "home made" by NBS staff >> at the old Beltsville, MD facility and moved to Ft. Collins. >> There is no longer an antenna for this transmitter and it >> will not return to the air. Trivia: The antenna was of >> such high-Q that a near-by thunderstorm system would >> often detune the system and cause the overload protection >> to trip the transmitter off. >> >> He suggests that a visit to the NBS website would be >> "informative". >> >> 73 >> >> Ken Kopp - K0PP >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[email protected] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> Message delivered to [email protected] > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [email protected] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
