[Elecraft] OT: Changes at WWV, WWVB

[John Marvin]

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
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