[time-nuts] 1pps signal presence with no GPS signal.
geoff36 at gmail.com
Thu Jul 7 18:37:37 EDT 2005
Ulrich Bangert wrote:
>If you want to play a save game, never (i.e. NEVER) use the 1pps alone.
Indeed, however there are a number of products out there that do, and in
theory they offer 1uS precision, but many astronomers have found out the
hard way that errors can be large with using the raw 1PPS from GPS.
Although discussion is currently with the Motorola family, there are those
of us tinkering with trying to get 'cheap' cost effective timing, using more
primitive GPS modules.
A few years ago I was involved in a project to track down why certain GARMIN
modules would drop the 1PPS. We even discovered a fault with the Garmin "16"
that its little brain can get so over worked trying to regain FIX, that it
'forgets' to control its own hardware resulting in 50 Hz bursts on the 1PPS.
Some astronomers have had errors of up to 40 seconds (a long way from 1uS).
Readers may be interested in a wee project I have developed that uses a
microcontroller to extract the time from GPS and create video text all in
one $2 chip - as per:
However my definition of 'precision' is about 10e10 different to the one
'tvb' would use ;-)
Regards, Geoff (New Zealand).
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