> -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Tom Van Baak > Sent: Wednesday, January 14, 2009 12:58 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] WWV / WWVH / WWVB > > > Kind of a shame they didn't use the unused bits in the WWVB > stream for > > some kind of checksum or error correcting code. > > Not really. At just 1 baud and with questionable reception in > many parts of the country, checksum bits aren't the answer. > > The usual WWVB trick is to collect as many minutes of data as > you want in order to increase confidence in your decoded > result. It allows you to pull a very weak signal out of the noise. > > This might be as little as 1 or 2 minutes; or depending on > time and location, it might be 5 or 10 or more minutes. With > this level of patient oversampling there are a number of > software tricks one can employ to pull out an error-free > timecode from incredibly weak or noisy signals.
It *is* effectively coded with forward error correction. Integrate for 10 minutes and you have a rate 1/10th code (considering a whole frame as one symbol) with a very simple coder (code symbol(i+1) = code symbol(i) + 1). (well, the code's a bit more complex, because it's BCD, etc.) _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
