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[aprssig] Local Event using RELAY?

AE5PL Lists HamLists at ametx.com
Thu Mar 31 12:22:08 UTC 2005

Apparently Wes's message was posted to the SIG so here is my response
that I sent directly...

First, you misquote my numbers.  Second, you misinterpreted what I said.
Third, you misstated Bob's alternate input frequency idea.

Let me explain, what my numbers said is that less than 7% of the packets
inserted onto 144.39 in the DFW area come from mobiles.  Of those less
than half cannot hear at least one other.  When you get down to it, 99%
of APRS in the DFW area is CSMA.  And I also said that APRS is NOT
ALOHA.  What you and Henk are talking about is transmitting
in-the-blind.  ALOHA (as I explained) is badly misrepresented by many as
simple transmitting in-the-blind which is what Henk and you imply.  It
is a much more complex protocol with characteristics that go far beyond
what APRS does.

Mic-E input via a smart digi (i.e. digi_ned) is NOT what Bob's alternate
frequency plan is.  His stated plan is to use a digipeater that listens
on 144.99 and transmits in-the-blind (although I think we convinced him
this was definitely a bad idea) on 144.39.  It is also to have stations
that can listen on 144.39 do so, NOT on 144.99 so ALL transmissions on
144.99 are in-the-blind and ALL transmissions by the digipeater onto
144.39 are in-the-blind.  Worse yet, the cross-frequency digipeater is
deaf to 144.99 while it is transmitting on 144.39 so it misses all of
the transmissions on 144.99!  And that, my friend, is why it is a bad

Setting up an alternate frequency with intelligent digipeating or gating
(which is being done in another area) with everyone doing their best at
CSMA is good and workable.  You do not transmit in-the-blind on your
Mic-E repeater.  Your posit is received as part of your voice
transmission and digipeated (using CSMA) onto 144.39.  No part of that
is in-the-blind.  And that is what this whole thread has been about.


Pete Loveall AE5PL
mailto:pete at ae5pl.net   

> -----Original Message-----
> From: Wes Johnston [mailto:aprs at kd4rdb.com] 
> Posted At: Wednesday, March 30, 2005 8:01 PM
> Subject: RE: [aprssig] Local Event using RELAY?
> Ah ha!!!  The light came on for me!  Henk and I are talking 
> apples to Pete's
> oranges...   Apples and Oranges...
> The important (yet subtle) difference is the dispairity 
> between a mobile's coverage area and a digipeater's coverage 
> area.  When packets are bouncing along from one digi to the 
> next, and  the digipeaters have a significant portion of 
> their coverage areas overlapping, then CSMA can work better.  
> The greater the overlap, the better CSMA works.  But since no 
> two digipeaters have 100% overlapping coverage area (what 
> would be the point?), CSMA will not work 100% of the time... 
> it's simply a function of the percent overlap.  I can see 
> from a digipeater to digipeater perspective, that without 
> CSMA, the network wouldn't work well.

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