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[aprssig] Fillin digi experiment

Pentti Gronlund pentti.gronlund at tut.fi
Sun Jan 17 21:55:29 UTC 2010

Bob Bruninga  writes:

> And THAT IS A FALSE TEST and IMPOSSIBLE to assure.  A very large 
> portion of APRS packets (if not HALF or more) that are SUCCESSFULLY 
> transmitted and digipeated on the channel are NOT HEARD at any given 
> receiver due to the fact that all digi's are suposed to digipeat the 
> same packet at the same time (in one slot time).  Hence, any station 
> or digi that hears these two packets at the same time with approxim-
> ately equal strength will NOT DECODE them.

Yes, you are just setting up your digipeaters in a wrong way.

Simultaneous transmissions should be avoided by all costs. I don't know
where this idea came from, but it does not work in the real world, and
never will.

Bob, do us a favour and stop yakking of this concept. It may suit SoCal
and some other extreme examples of crowded traffic, but it introduces
very bad network behaviour everywhere else.

> If you do not believe this, go visit a DIGI site or a FILL-IN site and 
> LISTEN to the channel and WATCH the monitored packts on the serial port.  
> You will see that far more than half of the time that the channel is 
> "busy" (Squelch open) there are no packets decoded due to collisions, 
> yet the channel is IN USE and is CARRYING VALID packets for others some-
> where else.

Been there, done that, unfortunately nobody printed the t-shirt. Many
of our systems are computer-based so I can bring up multiple monitor
windows on the screen. Most entertaining, dear Watson :)

Benjamin OH3BK

PS. We have been experimenting with these "vicious digipeaters" in
secrecy for a while, and they work well. You just have to set up the
digis to avoid transmitting over one another in your whole network :)
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