[time-nuts] WWVB Clocks don't sync anymore (revisited)

Eric Williams wd6cmu at earthlink.net
Wed Mar 20 13:28:41 EDT 2013


I also have a SkyScan clock that is claiming to be synced to WWVB, but is
slowly drifting off.  I've replaced the battery and it synced at least once
after DST conversion,  Two other WWVB clocks are working as they should.

On Tue, Mar 19, 2013 at 1:55 PM, Clint Turner <turner at ussc.com> wrote:

> A few weeks ago I posted a question/comment about some of my WWVB-based
> "Atomic" clocks no longer setting themselves properly. These two clocks,
> SkyScan #86716, would show the symbol indicating that they had set
> themselves, but their time was drifting away from UTC.  Interestingly, they
> *would* set themselves exactly once upon installation of the battery, but
> never again.
>
> Since that time, I've done a bit of digging around.
>
> The first suspicion was that, perhaps, the NIST had fudged a bit in the
> WWVB timecode recently, so I manually decoded a few frames and analyzed
> them:  Nothing suspicious there.
>
> The next question was if the addition of the BPSK somehow skewed the
> timing of the TRF's AGC/threshold - but logically, this didn't make sense
> since the clock *did* set itself exactly ONCE - and it wouldn't have been
> able to do this at all were this the case.  Out of curiosity I poked around
> on the board and found the trace containing the time code and found that
> despite the BPSK, its timing was exactly as it should have been:  No
> surprise there.
>
> This left the clock itself, so I did what any other Time Nut would do:  I
> built a WWVB simulator.
>
> Initially, I set it to a 2010 date - a time that I knew that the clock
> worked properly.  I had two clocks:  One that I'd just reset by pulling and
> replacing the battery while the other had been "stuck" for a few weeks, not
> resetting itself nightly as it should. I put both of these in the coupling
> loops from my WWVB simulator and over the next few days, the recently
> re-set clock happily synchronized itself while the other one with the 2013
> date was still "stuck."  I then reset that clock and it, too, behaved
> itself from then on.
>
> I then reset the clock on the simulator to a February 2013 date and time.
>  Initially, both clocks reset themselves to the current time and date at
> their next midnight, but after that, they got "stuck", never resetting
> themselves at "night" again.
>
> So, it appears to be a problem with "Broken Sand" (e.g. a silicon problem).
>
> For the morbidly curious, I have documented my efforts here:
>
> http://ka7oei.blogspot.com/**2013/02/did-nist-break-bunch-**of-radio.html<http://ka7oei.blogspot.com/2013/02/did-nist-break-bunch-of-radio.html>- The initial testing
>
> http://ka7oei.blogspot.com/**2013/03/yes-nist-did-break-**
> bunch-of-radio.html<http://ka7oei.blogspot.com/2013/03/yes-nist-did-break-bunch-of-radio.html>- The testing with the WWVB simulator
>
> 73,
>
> Clint
> KA7OEI
>
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