[aprssig] TAPR Differential GPS Reference Station
Boyd Prestwood K5YKG
k5ykg at arrl.net
Tue Apr 21 13:16:05 CDT 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
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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