Re: Beresfield Accident Findings

[mauried@commslab.gov.au (Maurie Daly)]

In article <894120844.101793@woody.hotkey.net.au> "Michael Walker" <walker@hotkey.net.au> writes:
>From: "Michael Walker" <walker@hotkey.net.au>
>Subject: Re: Beresfield Accident Findings
>Date: Sun, 3 May 1998 01:20:35 +1000

>I'm sure differential GPS is available for commercial use as I was reading
>an article not long ago that the FAA or whoever it is in America that
>controls flight paths and the like outside of airport limits was thinking of
>using it. If I recall correctly (and it was a while ago so if any experts
>are reading this who have more of an idea than I do, please kindly correct
>the information without flaming or any crap), the military had used it for
>some applications but had moved on and after a mandatory period, it became
>available for civilian use.


Differential GPS is widely available in Australia for commercial use,but its 
not free.
The ABC JJJ Network transmits the differential correction signals on one of 
its SCPC channels.
Differential GPS is only useful when you are relatively near (< 50 kms or so) 
to one off the differential transmitters as the further away you get then the 
greater the error introduced into the differential signal caused by the 
propagation delay.
You obviously also need a special differential receiver attached to your 
conventional GPS Receiver.
It wouldnt be of any value to trains as they are continuously moving and you 
couldnt guarantee that you were always withing range of one of the 
differential transmitters.

cheers
MD