[OZAPRS] Help with digi paths

[David and Ann Fraser]

Hi Andrew,

On Sat, 12 Mar 2005 05:24:01 +1000, Andrew Rich wrote:

> I can hear three digis direct

> My path is WIDE

> Three digis running UI-DIGI

> Why does this happen ?

> VK4TEC>APRS,WIDE <UI>
> VK4TEC>APRS,DIGI1 <UI>
> VK4TEC>APRS,DIGI2 <UI>
> VK4TEC>APRS,DIGI3 <UI>

> I would have thought UI-DIGI would have

> VK4TEC>APRS,WIDE <UI>
> VK4TEC>APRS,DIGI1 <UI>

> VK4TEC>APRS,DIGI2 <UI> ignore
> VK4TEC>APRS,DIGI3 <UI> ignore

> Cheers Andy VK4TEC

It looks like two or all three of the digis are set up with nice polite
Persistance and SlotTime values as per the values normally used on
connected mode packet channels, so that everybody shares the channel.

With APRS, the values should be such that digis transmit immediately so
that in your particular case, when you beacon, the three digis should
immediately retransmit your beacon without waiting a few milliseconds to
see if they might collide and probably wait for the other digis to
finish sending your beacon.  Thus you're seeing three digis individually
sending your beacon, instead of all three simultaneously.

Due to FM Capture Effect, you should only see one digi repeating your
beacon: the strongest one into your receiver.

The proper values for UIDIGI are Persistance=255 and SlotTime=1 but the
config files up to maybe a year ago (plus or minus) have "normal packet"
polite default values unfortunately, e.g. Persistance=64  :-(

With improper ('polite') values, people receive (in your case) three
times as many packets as they need (i.e. unneeded duplicates clogging
up the channel).

73 David.

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