[aprssig] APRS football tracking lesson learned
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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> aprssig at tapr.org
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