[time-nuts] WWVB Clocks don't sync anymore (revisited)
Clint Turner
turner at ussc.com
Tue Mar 19 21:27:59 UTC 2013
Someone pointed out a typo: I wrote model number "86716" where I meant
to write "86715" for the SkyScan clock in question. In the linked web
pages it is correct, however.
73,
Clint
KA7OEI
Clint Turner 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
> - The initial testing
>
> 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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