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kleppermaster wrote:
> The date time issue intrigues me as well. The instrument came with no
> batteries so there could not have been any ongoing calculations of the
> date and time (unless there is an internal long life battery I don't
> know about). It turns out the date is accurate, but the Hours, Minutes
> and Seconds are not correct. Furthermore, there seems to be no way to
> offset for odd minutes and seconds. It is possible to add or subtract
> hours to account for time zone. I would like to have it read UTC so I
> set it to 0 time offset.
>
>   
When switching on a GPS device it will need to receive 4 satellites in 
order to solve the following four unknowns: X, Y, Z and clock-drift. The 
clock-drift is the unknown quantity of time that the receiver is ahead 
of or slow to UTC. The satellites all have their own cesium clocks, 
which are quite accurate. Even these clocks do show clock drift 
(partially by relativity), but that is monitored by several ground 
stations world wide and corrected for. The receiver only has a cheap 
clock like in most pc's (fed by an on board battery). So in order to get 
a proper second-accurate time from your receiver you need to hook it up 
to an antenna and receive at least 4 satellites (and get locked onto 
them, so get a fix). The antenna is an active one, which means it has 
electronics on board that are fed by power through the coax cable. I am 
not sure what these electronics do, but you can imagine the difficulty 
to make one yourself.

Nicol�s



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