Daylight Losing Time: GPS Synchronizing VL?

At 05:23 02 November 2008, 309 wrote:
Well, it's time to set clocks back...and I noticed something
interesting today.

My VolksLogger's clock seems to run 15 seconds ahead of other GPS
units...and the US Atomic clock (which appears to be synchronized with
GPS time -- or vice verse -- per the readout from a Garmin GPS90).

I say the VL seems ahead...and this is based on seeing the minute
readout roll over ahead of the other GPS units...since the VL display
doesn't show seconds.

Normally, this isn't a real concern, but I've been using the VL to do
some performance flight testing on a power plane...and I noticed that
the events I recorded didn't match up with the trace on the VL.

Has anybody else seen this type of "synchronization" error?

-Pete
#309

The probably explanation is that the difference you are seeing is 14
seconds and there have been 14 leap seconds since GPS started up.

Leap Seconds are introduced because the earth does not rotate in exactly
24 hours and GPS relies on exact time.

Satellites transmit the leap-second correction in ephemeris data which is
broadcast every 12.5 minutes, so if your VL had had sight of the sky until
the next correction came in, it would show correct time.

Read http://www.u-blox.com/customersuppor...apSeconds.html
for a manufacturer's explanation.

Had your VL been without power for a long period? I would have expected
the RTC in the VL to keep a record of the current correction under normal
circumstances.
-

Tim Newport-Peace >
Skype: specialist_systems
http://www.spsys.demon.co.uk/icom.htm