[time-nuts] new WWVB BPSK dev board

[Bob kb8tq]

Hi

So, backing off a bit:

Assuming you are going to compare two data points a bit over 24 hours apart (100,000 seconds):

Accuracy of reading pair			Result pp 		Result sci

100 ms						1 ppm			1x10^-6
10 ms						100 ppb			1x10^-7
1 ms						10 ppb			1x10^-8
100 us						1 ppb			1x10^-9
10 us						100 ppt			1x10^-10
1 us							10 ppt			1x10^-11

At 100 ms, you need to go for a *lot* of days before you get out of the “that’s interesting ….. yawn …”
category. Since it’s a pair you are concerned about, each might have a 50 ms error to get you to the
100 ms total. It’s still plenty good enough for a typical wall clock. 

At one day you don’t cross into “as good as a free running Rb” territory until you get below 100 us. 
That’s also the point you hit roughly the typical GPS module’s performance at 1 second. 
If you want to get a “Time Nuts” grade solution, microseconds are indeed the units to worry about.

Assuming you hit can 100 us per pair, and want to get into the 1 to 10 ppt range, you are out around 
100 days for each “run”. That seems like a long time to wait. 

Since one period is 16.667 us, hitting well below 100 us implies keeping track of which cycle is which. Getting
to 10 us is just above a 180 degree phase error and 1 us is still above 10 degrees. 

I’d say that for a practical “Time Nut" device … you need the equivalent of cycle tracking at the very least. 

Indeed, as mentioned by … somebody …. this all can be done and … ummm …. has been done for similar
signals by …errr …somebody :)

Bob

> On Dec 4, 2018, at 3:08 PM, David G. McGaw <david.g.mcgaw at dartmouth.edu> wrote:
> 
> That is the specified jitter.  They have also said in communications that it has about 50mS resolution.  That is as close as they are willing to say a system can be synchronized with it.  Perhaps someone will discover a clever way to enhance that.
> 
> BTW, I have been told it has also been successfully tested for lock in Brazil.  Is there anyone in Australia want to give it a try?  Perth is almost directly opposite Fort Collins.  :-)
> 
> David N1HAC
> 
> 
> On 12/4/18 2:00 PM, Hal Murray wrote:
> 
> 
> 
> 
> As was said, IRQ delay is +/-100 mS from the second edge, hardly what a
> Time-Nut is looking for.
> 
> 
> 
> There is no problem with a delay as long as it is constant.  If I know what it
> is, then I can correct for it.
> 
> The problem is the noise/jitter on the delay.  I'm sure somebody will have
> data soon.
> 
> 
> 
> 
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