[aprssig] APRS football tracking lesson learned

Robert Bruninga bruninga at usna.edu
Mon Dec 12 14:19:54 CST 2016


6db is half the range.

A good thing to remember when operating low power for an APRS event out of
area…



We have been using 10W trackers for our local events with great success and
local digipeaters.  So this year, rather than putting 50W APRS radios in
the four football tracking vans, we just put in some 10W trackers instead.
A lot less hassle.  Just plugged into the cig/lighers.



OOOPS.  Tracking was poor.  This is probably due to some  aging of our
local digi infrastructure (which I had not paid close attention to for
years) and running lower power than our typical 50W mobile commuting.  With
a difference between 10W and 50W is 7 dB, and remember that  it takes 6 dB
to double range.



Then we also found out that the self-reported “PHG” range circles for most
digis were off by another factor of two….



The PHG circles in APRS are designed to be approximately HALF the
theoretical horizon due to the fact that packet takes at least 6 dB more
signal than voice for error free packets.  But on the APRS.FI map, almost
all the digipeaters  plot outlandish predicted ranges.   We might ought to
re-check these PHG circles.



This map shows coverage in maryland, but look at the actual dots.  No hits
in central Maryland area: http://aprs.org/digis/usna-digis-2016.png



Just some data points… and a reminder that we cannot take the APRS
infrastructure for granted….



Bob, WB4APR
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