Re: It is getting easier

["David Lesher / hated by RBOC's in 5 states" <wb8foz@wauug.erols.com>]

Bill Frantz sez:
> 
> At 11:25 PM 11/14/96 -0800, Lucky Green wrote:
> >If I remember correctly, some of the newer transponders used on 
> >commercial aircraft actually transmit GPS data back to the controller in 
> >real time. I wonder how long it will be before the FAA will include such 
> >information in their database.
> 
> I don't think new transponders make much difference.  The old ones heighten
> the radar image of the airplane which gives an accurate 2D position.  This

I missed how this got the 'Punk material, but a friend is running
parts of a test of this.

The en-route radar is roughly the same age as those IBM 360's in the
Centers that you keep hearing about. 

The current approach is radar, [?2 ghz] with interrogation of a
1 ghz transponder via the same array. The xponder has 4 octal digits
and {Mode C} the altitude from an accompanying encoding altimeter.

So the alternate approach is a GPS receiver with a transponder
replying to interrogations with position and altitude. For the most
part, in the "en-route" stage, the futzing by DOD is not a concern
-- all receivers in a given area are equally deceived. [Recall that
the goal is to avoid Delhi incidents.]

During departure and approach, the a/c will use 'differential GPS'
whereby a GPS RX at a known benchmark on the airport will broadcast
what error IT sees. [Errors are roughly linear within X mile zone.]
DGPS will be as good or better than many existing Instrument Landing
Systems, i.e. a few feet in all 3 dimensions...


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