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[aprssig] Using APRS without GPS?

Robert Bruninga bruninga at usna.edu
Fri Jun 30 15:00:08 UTC 2006


> I run scout camp where we break the camp up into four 
> groups and they walk from base to base throughout the 
> weekend. I'd like a setup to monitor their progress.
> What are my options regarding trackers...?

If this requires only 4 trackers, then this could work well 
as a typical APRS high tech solution.  But once you have APRS, there
are usually far more things you want to track and display....

SO, do not overlook the low-tech solution as well which is
simply making a map of the camp and "numbering" every 
interesting location.  THen just the simple report of a
"number" will update all APRS maps and displays throughout
camp with the current location of all participants.  This can
be done with voice, DTMF or a D7 HT. 

This track-by-points has been in APRSdos since 2002:

http://www.ew.usna.edu/~bruninga/D7points.html 

Using number-points reporting without GPS avoids these problems:
1) Keeping GPS units up and operating with all groups
2) GPS tracking problems in heavy foliage
3) Having to keep the GPS's running all the time and
    having to supply batteries for all that stuff
4) Erroneous positions due to erroneous GPS data
5) It works indoors and just about anywhere

This alternative is Someone with a radio in each group simply 
reports by voice (or DTMF) "we are entering base #13", and 
the APRS  sysop simply moves that group's object to location 13. 
This automatically then transmits that object to ALL APRS 
displays in the camp so that everyone sees the movement.

This can be done automatically with APRStt.  The Touch-Tone
version of APRS that *any* HT can enter data with.  Just
press something like XX*YY on the DTMF key pad and the 
central APRStt will convert that to APRS packet and update
all APRS displays throughout the camp....

See http://www.ew.usna.edu/~bruninga/aprstt.html 

APRStt then also speaks voice information back to the
DTMF-only users so they also are informed on new reports
such as "Team XX arrived at YY"...

And If you are running good APRS software that dead reckons,
then it can even show moving groups as they walk from
base to base.  And the radio consumes far less power than
a GPS and radio together.  Plus ANY HT that the scouts
already have, including cheap FRS can be used.

Without APRStt, you can use the Kenwood D7 HT's either
with GPS as plug-and-play, OR they can be used
without the bother of GPS as above, by KEYING in 
the 2 digit number themselves and the internal TNC
can transmit it to all APRS monitors throughout camp
without any human intervention.

So many options... without the encumberance of GPS...

Oh, and APRSdos can run on a $5 junk laptop from any
hamfest even without a hard drive since it can boot and
run from just a single floppy.  THis is pretty good for
low-cost implementation at a camp.  Presumably the low-
tech worthless laptops wont walk...

de WB4APR, Bob





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