[aprssig] Viscous digipeating (was: Airborne Digis)

[Wes Johnston, AI4PX]

The recommendation for aprs is DWAIT 0, which means that all digi's will TX
at the same time.  I understand what you mean about FM simulcast frequency
being dead on.. but there's more to it than that different TXDelays also
will cause the seemingly identical packets to not be the same.  It is easy
enough to move a home QTH antenna so that it only hears one digi however.
And in a mobile circumstance, it is very very likely that you won't hear
both digi's anyway.

Wes
---
We are learning a lot more about Chicago-style politics than I ever wanted.


On Sat, Sep 19, 2009 at 12:12, Pentti Gronlund <pentti.gronlund at tut.fi>wrote:

> Bob Poortinga writes:
>
> > Just because a certain digipeater didn't hear it, doesn't mean that is
> > wasn't digipeated.  This "solution" adds needless congestion to the
> > APRS frequency.  Every digipeater which hears a packet that needs
> > digipeating should digipeat it without delay.  The FM capture effect
> > takes care of collisions.
>
> When viscous digipeating is applied liberally instead of plain-jane
> stupid WIDE1-1 digipeaters, you will get rid of most of the congestion.
>
> > Also, if two digipeaters are using "viscous" digipeating, how do you
> > determine how long to wait?  If they both wait the same time, you
> > still end up with a collision.
>
> They don't. AX.25 devices never do, they add some random delay before
> transmitting.
>
> I am truly sorry but I do not believe in FM AFSK simulcasting without
> right-on-the-target frequency and timing standards. All you will get
> is howling and corrupted packets. Been there, etc.
>
> We use 64 for persistence and 100 for slottime at most places. It en-
> ables the patchy network to send the packet from one digipeater at a
> time. The beauty in this is that also the downlink works quite perfect
> with only 5-10 watts of power.
>
> I have to confess that we got rid of most congestion a long time ago
> by making the digipeaters reject position packets from too far away.
> We also stopped gating message traffic from the internet, as none of
> the current igate software packages can effectively filter out message
> traffic to non-local stations.
>
> Benjamin OH3BK
> --
>                Live Reports from the Taxman's Paradise!
>
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