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[aprssig] Local Event using RELAY?

AE5PL Lists HamLists at ametx.com
Wed Mar 30 22:46:38 UTC 2005


> -----Original Message-----
> From: Henk de Groot
> Posted At: Wednesday, March 30, 2005 1:45 PM
> Subject: Re: [aprssig] Local Event using RELAY?
> 
> Yes, I know. But when you are unable to detect any carriers 
> of the other APRS stations because they are too weak or 
> hidden from you then, in those cases, CSMA just sees a clear 
> channel and hence transmit whenever there is something to 
> tranmsit (with a short delay because of the persistence and 
> slottime setting but otherwise pure ALOHA behaviour).

Maybe I can help those of your on this bandwagon with a few numbers of
my own (which, by the way, are real-world numbers taken in the DFW area
which is an extremely high density area according to Bob's web site).
Well over 80% of the packets seen in the DFW area are either digipeated
packets (packets which a digipeater has repeated), or packets originated
from a wide area digipeater (beacons, etc.).  So, that means that less
than 20% of the packets on 144.39 are actually originated by
non-digipeater stations in the DFW area (actually, less than 10% are
when you eliminate packets from outside the area).

Hmmm.  So if I use your statements of "fact", those stations generating
10% of the packets are blind to each other AND to the wide area
digipeaters.  Folks, this just ain't so.  Of the stations generating 10%
of the packets, only about 20% are mobile or portable.  The rest are
homes, weather stations, etc. with reasonable antennas.  So we are
talking about maybe 7% of the originating packets coming from stations
that might be "hidden" to each other but are NOT hidden to the stations
generating over 93% of the packets.

Bottom line: MOST of APRS is CSMA, not blind transmissions as you put
forth.

73,

Pete Loveall AE5PL
mailto:pete at ae5pl.net 




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