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[aprssig] TAPR Differential GPS Reference Station

Boyd Prestwood K5YKG k5ykg at arrl.net
Tue Apr 21 18:16:05 UTC 2009


I bought, assembled and tried out the TAPR DGPS Ref Station way back in 
the nineties.  I still have it but never pressed it into actual 
significant operation on-the-air after the trials.

However it was my understanding that the site from which the Ref Station 
transmitted had to be surveyed for "exact" coordinates and those 
coordinates were entered into the Ref Station.  With an internal 
algorithm, the DGPS Ref Station would then transmit its corrections as 
ASCII text RTCM-104, not NMEA-0183, and individual fixed and mobile 
stations would receive them via their individual TNCs (using a 2-way 
data cable) and route them to their GPS receivers which would then 
correct their coordinates (having been received from the GPS satellite 
constellation).  This afforded each individual station (mobile or fixed) 
to transmit their coordinates with greater accuracy.  However with the 
format of "DD.MMmm" and "DDD.MMmm", that extra accuracy enabled by the 
DGPS Ref Station's corrections wasn't realized to any practical degree.

It was necessary for the DGPS Ref Station to transmit these corrections 
about every 15-20 seconds and given that high beacon rate along with the 
unrealized accuracy usable, it was decided in the NNJ, SNJ and EPA 
sections that we wouldn't put such a station on the air.

What I don't remember was any APRS client program having anything to do 
with this method.  I ran APRSdos from 1993 until UI-View32 became 
available and my DGPS Ref Station never had any connection with the 
client softwares.  My memory could be rusty... all this was a long time 
ago!

Just an FYI.  Lemme know if and where I went wrong!
73 de Boyd Prestwood K5YKG (ex-W2HOB, former SEC, SNJ ARES)
Now living in Houston, TX





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