[time-nuts] GPS receiver time message offsets to 1PPS (updated)

Mark Sims holrum at hotmail.com
Thu Jul 28 13:45:42 EDT 2016

The Skylab is effectively useless for sub-second timing.  The message arrival time periodically jumps around,  up to +/- 300 msecs.  There are a couple of values that it seems to prefer, but any value can be seen.

NMEA works a lot better on most receivers that I expected.   They send several messages a second (and depending upon the receiver the time can appear in more than one message... Heather has a hierarchy of preferences for which message to get the time from if it sees it in more than one message.   By sending all those (rather long) messages each second, one might expect quite a bit of variation in time message arrival, but this does not appear to be the case (except for the Skylab).  It is also interesting that most NMEA receivers have their time message come out around 300 msecs +/- 100 msecs.  For a generic NMEA receiver, Heather uses a default correction value of -300 msecs.


> There is the Skylab SKM53 at 37.8 ms. I've never seen one of those, so no guess about that one.

The surprise in the crowd is the Res-T SMT at 63.7 ms. I wonder what they messed

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