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[aprssig] ALOHA Circle Calculation

Bob Bruninga bruninga at usna.edu
Sun Aug 1 19:21:50 UTC 2010

> Would I be correct to assume that the ALOHA Circle
> of any APRS station (or packet station in general, I
> suppose) would be the radius of the most distant
> station heard direct?

No.  But maybe yes At Dayton, or in LA maybe.  But that is not really how it works.  It is the circle that contians a FULL network.  Meaning all the packets saturate the channel and adding more stations just reduces the reliability of the network beacuse of collisions.  The algorithm works in Wyoming as well as Los Angeles, with the density in Wyoming maybe yielding a 150 mile circle and in LA, a 15 mile circle.

As I write this, I am near the beach in Lewes Deleware and was just looking at the Aloha Circle on my map.  It just about perfectly circles all the stations on the map.  This is good news, because it means no SPAM is coming in from areas beyond what the channel can handle.

Compared to 2004 when we came up with the concept, I was seeing 300+ stations over 7 states and the channel was wall-to-wall packets and the circle was much smaller.  Now that everyone has finally gotten the message to drop back to WIDE2-2, the channel is much quieter, yet I can see everyone in the state easily and reliably.  I'm seeing 116 stations...

See www.aprs.org/aloha.html


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