On 08/15/2013 10:22 AM, David Taylor wrote: > On 15/08/2013 08:34, Rob wrote: >> David Taylor <david-tay...@blueyonder.co.uk.invalid> wrote: >>> On 14/08/2013 17:44, Rob wrote: >>> [] >>>> How does a "good" receiver know the correct time? Does it rely on >>>> local (backed-up) storage, or is there some way of receiving it via >>>> the almanac? Or are "good" receivers hardwired as well, only with >>>> a different valid span? >>>> >>>> I would not be surprised when "good" receivers turn out to have just >>>> a different moment or mode of failure. >>> [] >>> >>> Some receivers have battery backup, in fact all but one of the receiver >>> types I use have this. >> >> Ok but what happens when the battery is replaced? > [] > > Hope and pray? Wish for a large capacitor or flash-rom? > > I had thought that either ephemeris or almanac data might contain the > real UTC time, but apparently it does not. Obviously a system > designed too far in advance of the Year2000 fuss and bother! They completely avoid it by not numbering it that way. They have their own numbering scheme that fit's the system, and the conversion over to UTC is an added feature. It's all in ICD-GPS-200 for the current set of details, and in the ION red book series for the early stages.
GPS and GPS problems is best understood if you realize that everything is counted in the GPS clock machinery with it's own set of gears. Conversion isn't that hard and it is done every second in the GPS receiver. Cheers, Magnus _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
