[amsat-bb] Re: GPS Time observation

[Alan Cresswell]

Well the most likely explanation would seem to be related to your GPS
display routine.  If you are getting accurate position information the
timing from the satellites must be within a few nanoseconds.  The satellite
time currently differs from UTC by plus 15 seconds because UTC is retarded
by one leap second on a regular basis but the satellite time is not altered.
The satellites broadcast this offset from UTC but only every 12.5 minutes.
It is not unusual for a GPS display to have a relatively low priority
compared to the intensive position calculations and give a time display that
differs by a second or two from UTC.

73
Alan
ZL2BX



-----Original Message-----
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of Dave Guimont
Sent: Thursday, 2 February 2012 18:29
To: Vince Fiscus, KB7ADL
Cc: amsat-bb at amsat.org
Subject: [amsat-bb] Re: GPS Time observation

Interesting question, Vince...am sure someone on here will be able to 
answer it. I know at one time the civilian population was restricted 
from the most accurate location, and as I also remember the military 
accuracy was within a centimeter if several observations were 
taken...Nice to see your smiling face on here, my friend...

Anyone?

73 Dave

>I have an old GPS unit, a Magellan explorist 210. It's fairly 
>accurate determining position. After it has acquired about eight to 
>ten satellites the position error averages between 20 to 35 
>feet.  Now the question, the other day I was looking at one of the 
>information pages the unit can display and on it, it gives the time 
>in UTC. Just for fun I thought I would see how close the time was to 
>WWV. I was surprised to see the unit was between one to four seconds 
>off over various tests compared to WWV. IS this typical of all GPS 
>units or do some display the time of day more accurately?
>
>KB7ADL
>
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            73, Dave, WB6LLO
                dguimon1 at san.rr.com

                    Disagree: I learn....

               Pulling for P3E... 
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