[time-nuts] WWVB Now a Monopoly

Jim Lux jimlux at earthlink.net
Wed Sep 26 23:22:36 UTC 2012


> What would annoy me is less-than-full disclosure of the transmitted
> signal and its properties.  For example, there's a claim in the paper
> that the (31 26) Hamming code used can detect double-bit errors in the
> encoded time.
You are right.  The standard Hamming code: detect and correct 1
(3,1)
(7,4)
(15,11)
(31,26)
Add a parity bit and you can detect 2 errors.

There's also an (11,8) code that can detect 2, correct 1
And a (72,64) which works and uses the same number of bits as a (9,8) 
parity check, with the advantage of detecting 2 and correcting 1.

Maybe there's another parity bit in the system somewhere, too.


I think detecting double-bit errors would require an
> additional parity bit, and that the assertion in the paper is just a
> boo-boo, but I also keep wondering if the claim might in fact be true,
> that there might be a really clever way to use that with something else
> in the signal to detect double-bit errors, and the paper just isn't
> pointing that out.  That would be annoying.
>
> Dennis Ferguson
>
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