[time-nuts] June 30 2015 leap second

Hal Murray hmurray at megapathdsl.net
Tue Jan 6 22:41:10 EST 2015

time at patoka.org said:
> The question is how usually GPS modules handle leap seconds ? Is it
> satelates who send UTC time to GPS module or GPS module has firmware with
> leap second information hard-coded ? 

The satellites send GPS time with a low bandwidth footnote that provides the 
offset to UTC and another optional footnote with the time of the next leap 

I think you can see this as a 15 second jump if you watch a GPS receiver 
doing a cold start.  I mean really cold as in no memory at all rather than it 
has battery backed memory but has been off for several months.  After several 
months, the RTC has probably drifted and/or the almanac is no longer helpful, 
but the UTC offset probably hasn't changed.  (especially for the past few 

It might be fun to warm up some low cost GPS receivers just before the great 
leap, power them off for several weeks around the leap, then see how they 
work when starting up post leap.  The question is do they remember the next 
leap as well as the (old) offset.

These are my opinions.  I hate spam.

More information about the time-nuts mailing list