Hi, On 08/14/2013 03:54 PM, unruh wrote: > On 2013-08-14, Mark C. Stephens <ma...@non-stop.com.au> wrote: >> Um Let's see, Datum was bought by Austron, who was bought by ... etc. >> For collectors such as myself, having this 'mature' equipment still working >> is great. >> >> Looking at Mr Malone's code, he added 2 lines which enabled NTPD >> compatibility with GPS receivers that would have long ago have been sent to >> the TIP as waste. > It is however fragile code. Ie, all kinds of situations could arise in > which it would give the wrong time. Now, you may say that there are > situations in which it will give the right time when, without the kludge, > it would give the wrong time. This addresses a known feature of the GPS system, common over a large range of receivers. The differences between them lies in which GPS week they flip over (GPS week 500, 512 and 729 from the top of my head). The failure they have is not in their operation, but in their production of a "human readable date".
This is what I have proposed elsewhere (on time-nuts) and it is a sound solution considering the situation we have where the ICD-GPS-200 through it's many revisions have not provided additional bits for the L1 C/A code signal. For the L2C (and I assume also L1C, but I haven't checked yet) signal additional bits exists, but very few recievers have that support. I recommend reading the time-nuts backlog on this issue. Among the alternatives you have, it's ditching an otherwise perfectly operating GPS receiver or use the fact that the 1024 week wrap-around is bound to happen, is predictable as a systematic effect from how the GPS C/A data is structured and re-occurs over the fleet of GPS receivers. Do note that the GPS receivers does compute leap-second info correctly regardless of this 1024 offset hickup, as that information is structured modulu 1024 weeks. Cheers, Magnus _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
