[aprssig] RE: APRS Question

[Robert Bruninga]

> ...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