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Originally Posted by rogerg
Ron, I'm afraid I'm more likely to have a GPS than a short wave radio, and I don't have a GPS  I have to admit, I'm a little confused at how a GPS can be considerred an accurate time device, with 2+ second delay between land -> sat -> land, ! |
Hi Rog,
In fact, it is these finite delay times (even at the speed of light) that are
at the very heart of how GPS can be used to determine your location and
also to provide you with very accurate time.
How GPS can supply very accurate timing is
very clever.
If you are really interested, I recommend this tutorial here -
http://www.trimble.com/gps/index.html which will provide
a better explanation than could be made by this short response.
You will need a free Shockwave player plugin to view the graphics if
you don't have one.
In the end, the time available from your GPS receiver does not suffer the
propagation delays experienced from using WWV/WWVH on shortwave.
However, there are various relationships between UTC and GPS time
(some of which is to do with the insertion of leap seconds) that
serious pratictioners need to be aware of (and that are well documented on
the web).
Since some GPS receivers only have serial comms ports that run at
low speeds, delays are often more significant as a result of this style of
comms. More elaborate receivers offer an alternate interface as an
accurate timing source.
By the way, did you know the Europeans are about to launch their own
constellation of satellites that will both compete with and complement the
American-built GPS constellation?
Best Regards
Gary Kopff
Mt. Kuring-Gai