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Re: Time references (UT vs. GPS) Whoa, there!



OK, as usual, once someone sends an email, they find the information 
they're searching for in less than 21 microseconds after hitting 
SEND:

>From the US Naval Observatory web page: 
              http://tycho.usno.navy.mil/gpstt.html

"GPS time is not adjusted and therefore is offset from UTC by an 
integer number of seconds, due to the insertion of leap seconds. The 
number remains constant until the next leap second occurs. This 
offset is also given in the navigation (NAV) message and your 
receiver should apply the correction automatically."

So while there IS a 13-second difference between the "GPS time" and 
UTC, users shouldn't see the difference because the receiver has been 
told to adjust for the offset.  Which begs the question why Laura is 
seeing the offset.

But, at least, now, I don't have to worry about the difference when 
I'm using the GPS to synch up the meteor scatter or EME station with 
UTC.

73 Wayne N5WD

On Mon, 7 Jul 2003  NX7U wrote:
>I found this interesting...it may be widely known but it wasn't by
>me ;-)
>
><http://www.leapsecond.com/java/gpsclock.htm>
>
>
>Definitions - pulled from the Leapsecond website:
>UTC, Coordinated Universal Time, popularly known as GMT (Greenwich
>Mean Time), or Zulu time. Local time differs from UTC by the number
>of hours of your timezone.
>GPS, Global Positioning System time, is the atomic time scale
>implemented by the atomic clocks in the GPS ground control stations
>and the GPS satellites themselves. GPS time was zero at 0h 6-Jan-
>1980 and since it is not perturbed by leap seconds GPS is now ahead
>of UTC by 13 seconds.

<snip>

To which VE7LDH added:

>I work with systems that are synchronized with GPS, and
>that 13 second difference to UTC is very much part of my
>soul nowadays.

OK, this has been bugging me no end - I simply don't see any
13-second difference between (a) my receiver hearing WWV over the
air, (b) an atomic clock that synchs up with WWVB every evening and
(c) my Garman GPS-12.  There IS NO 13 SECOND DIFFERENCE that I can
see!

Now, I saw the reference to the 13 second difference on the web page
that Scott referenced, but I can't find it anywhere else in the
references I've looked at.  Is this merely another urban legend?

Or, is my GPS unit really 13 seconds slower than it should be?

Anyone care to duplicate or dispute my observation?

73 Wayne N5WD

--
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 R. Wayne Day N5WD Ft Worth,Texas n5wd@charter.net
QRV: IRLP node 3852  146.450smpx PL 100.0 Bedford, TX
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