[aprssig] APRS football tracking lesson learned

KF4LVZ aprssigZbr6 at acarver.net
Mon Dec 12 15:05:27 CST 2016


Is this why Navy lost?

I don't know what vehicles you use but I ran a 50 W mobile from a
cigarette lighter socket for over a year.  Assuming 50% efficiency plus
electronics (CPU, etc) that's about 9 amps at 12 volts.  Most sockets
are fused for greater than that (my car's socket is fused from the
factory for 20 amps).  The quick current spike from a transmit is not
much different than the inrush current of the heating element.

On 2016-12-12 12:19, Robert Bruninga wrote:
> 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 <http://APRS.FI> map, almost all the 
> digipeaters  plot outlandish predicted ranges.   We might ought to re-check 
> these PHG circles.
> 
> Thismap shows coveragein 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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