[aprssig] Differential GPS?

Earl Needham needhame1 at plateautel.net
Fri Apr 24 00:20:46 EDT 2009

Robert Bruninga wrote:

> Does anyone do differential GPS in APRS?
> There is a provision in APRS that will allows someone to connect
> a TNC to a GPS differrential receiver and then transmit those
> corrections to a mobile on the APRS channel.  We experimented
> with it in the early days, but I just don't see that it is
> something we need to continue to support.
> Reason being that we found  you needed frequent DGPS
> transmissions to have any value, and the APRS channel could not
> handle a DGPS transmission every 15 seconds just for one or two
> people to use it.  Yet, if you reduced the DGPS rate to say once
> a minute, then the DGPS data was so stagnant, that there was
> little value added.
> Of course it was a benefit back when selective availablility was
> on, but now that the US government leaves it off, we don't need
> DGPS (integrated into APRS).  Also, back then the DGPS receier
> cost maybe $50,000.  Now, I think anyone can buy one at the boat
> store?  And if he needs it, he feeds it directly into his own
> GPS.
> Can we remove the DGPS-on-APRS-channel function it to save code?
    My gut feeling is that you should go ahead and drop it.  I use DGPS 
in the 18-wheeler, but I do it directly from a GBR-21 to my GPS-V.  I 
don't think I've run across another person using DGPS in several years.

    WAAS is available, and the accuracy is usually only 1 or 2 feet 
"worse" than with the GBR-21, and most of us will never need that kind 
of accuracy anyway, at least not for tracking a vehicle, storm spotting, 

    7 3

KD5XB -- Earl Needham
Clovis, New Mexico DM84jk
Quoting from the Coast Guard: ZUT

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