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ZL3AI > APRDIG 14.05.07 01:02l 95 Lines 3272 Bytes #999 (0) @ WW
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Subj: [APRSSIG] Vol 35 #6, 2/2
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From: ZL3AI@ZL2BAU.#79.NZL.OC
To : APRDIG@WW
Message: 7
Date: Mon, 7 May 2007 09:23:50 -0400
From: "Robert Bruninga" <bruninga_at_usna.edu>
Subject: [aprssig] APRS and the Interstates
>...this LINK is what a mobile running [the path]
>WIDE1-1,WIDE2-1 gets (using a full power D700]...
>
>http://www.findu.com/cgi-bin/track.cgi?call=n7xuc-7&geo=usa.geo&start=10000
>
>Places with the biggest gaps... are Nebraska, Eastern
>CO, TX panhandle, Georgia (Atlanta to Savannah),
>Ohio (especially I-70).
The biggest bang for the buck is the Interstates. We somehow need to
educate the broad amateur community to invest in digipeaters in those areas
in their states that may not serve them directly in their own back yards,
but that serve the traveling ham community where they need it most.
APRS is a "service". Invest in it even if you don't use it...
Bob, WB4APR
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Message: 8
Date: Mon, 7 May 2007 09:45:24 -0400
From: "Robert Bruninga" <bruninga_at_usna.edu>
Subject: [aprssig] RE: APRS Question
>...regarding APRS messages.
>Do they follow the same path statement as your
>regular beacon in the D-700 ?
Yes. And also in most APRS clients too.
>I saw my own message ping back about a minute
>after the local DIGIs sent it the other week.
May have gone through an Igate and the recepient may have been in the same
area, and so an Igate sent it back to RF?
>Also I know with UI-View and a internet connection
>to the APRSIS, it is easy to send a message beyond
>your max hop distance using "send reverse" path
>through the internet.
There are no "paths" through the internet. Everything heard goes in,
anything that comes out uses only the local TX path of the local Igate.
>Can that be done from RF ?
Reverse pathing can only be done on RF. And under the New-N paradigm, it
works better than ever, since now all paths (using WIDEn-N) are fully
traced.
>Would I need to know in advance the closest DIGI call sign in Baltimore ?
No, messages to 2 hops work fine with a 2 hop path of WIDE2-2. But to go
any further without QRMing too much of an area, you need to specifically
select your path as in WIDE2-2,DIGI3.
I wouldn't try going beyond 3 hops becase the probblities of success go
down very rapidly.
>I like to experiment and learn.
A path of DIGI1,DIGI2,DIGI3,DIGI4, could go that far, but you would never
expect an ACK. But if you are communicating with a friend over such
distances, then as long as each of you REPLIES to each incoming message to
let the other guy know you goit it, you can have reasonable minimal 2 way
communications. But if you wait for ACKS, it will never happen.
This is easy to understand. If the chance of a collision at each digi is
50%, then after 2 hops your success rate is 25%. After 4 hops it is 6%.
BUT now then the chance of the ACK getting back is 6% of 6% or only 0.004.
But the chance of your friend's message getting back to you is still 6%.
Sending a message via four D1,D2,D3,D4 hops is not QRM, since it makes only
4 packets. A WIDE2-2 packet in most areas can generate far more.
WB4APR, Bob
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End of aprssig Digest, Vol 35, Issue 6
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