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[aprssig] Appalachian Trail Golden Packet Event update

Robert Bruninga bruninga at usna.edu
Tue Apr 7 14:38:40 UTC 2009

[Regarding the AT trail Golden Packet event:]

> I'd like to know what changed -- a few years ago
> I got chewed out royally for reporting the following:
>>> =3703.52NN12048.48W#Todd's Big Motgage {UIV32N}
>>> Station is 1002 miles from me and appears 
>>> to have made it all the way here on 2 meters.  
>>> Looks like it took 10 hops to do it, though...
> I didn't even SEND the packet and yet I was 
> in trouble over it --  and now we're actually 
> ENCOURAGING such operation?  I'm confused, I guess.

Ah, that's a good question.  There are many differences.  And it
is understanding those differences within the context of the
conditions that makes all the difference.  These are the

1) This experiment is not on the national shared APRS channel
2) It is on a dedicated one-time frequency
3) It does not use a FLOODING algorithm (TRACE7-7)
4) Which can generate nearly 200 packets over half the USA
5) It uses LINK7-7 in a linear network which makes only 7
6) The network is physically layed out as a linear network only

This ad-hoc one day event is set up from the get-go to be a
linear system and to demonstrate the long haul potential of
packet (in linear links on a QRM free channel).  Such a system
with 2 or 3 hops can be used to get an emergency comm link
re-established in an emergency for low rate Communications.  Of
course links beyond 3 or 4 hops have lower and lower
probabilities (proportioanl to N squared), and we know in the
1990's that such links are deminishingly poor for CONNECTED
packet.  But for APRS using message-pushing (without acks) along
a low QRM linear set of links the success rate only deminishes
acccording to N and can be effective.

Conversly, the APRS national channel is a local communications
and info distribution channel in all directions simultaneously,
so flooding beyond the local network is QRM to everyone else.
Hence the requirment to keep all packets local (WIDE2-2 or
less).  In such a network where most digi's can hear 4 other
digis, the deminshing of success is N to the 4th power!
Virtually impossible.

Hope that helps.
Bob, Wb4APR

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