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[aprssig] Appalachian Trail Golden Packet Digipeater

Robert Bruninga bruninga at usna.edu
Wed Apr 8 02:18:54 UTC 2009


The battery required to run a D700 as the digipeater for the AT
trail event for 5 hours has been estimated and a photo about 60%
down the page:
www.aprs.org/at-golden-packet.html

The D700 draws about .6 amps with mild audio and with a 20% TX
duty cycle on the TX, about 4.5 amps or less at medium power
(10W).  This adds up to about 1.5 amps average power.  SO for
the hike-up mountain sites, you will need to either carry a 7.5
AmpHour battery or just a tiny 1 amp-hour or so battery and a
1.5 amp solar panel (or any mix inbetween).

For this first attempt we only want to run D700's since their
TNC/Radio interface is a fixed, optimized known quality. What we
want to avoid is the 10-to-20 dB loss in weak-signal performance
seen on many existing APRS systems that were plugged-n-played
without any adjustment of tones, levels, skew, deviation or
quality.  A D7 or D700 will decode another D7 or D700 with only
a single LCD "S" meter segment lit.  But sometimes you can see
nearly  FULL scale packets not decode because they are horribly
distorted and skewed.  We don't want any of those unknowns on
this first golden packet event.

With the radio and battery and a lightweight fiberglass push-up
mast and antenna, the complete digipeater system can weigh under
15 lbs.  And fortunately, so far, of the 15 stations, only two
have to be hiked in, and only one other one has to be carried 66
feet vertically up a ladder.

Enjoy the hike.  But remember, this is a good demo of how easily
an emergency APRS digipeater can be fielded for events or
emergencies.

Bob, WB4APR




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