[aprssig] More efficient use of channel capicity throughshorterpackets

[Robert Bruninga]

> And after TXD, you've got a minimum of ...
> Also, I think you'll find that most ham rigs are slower to key
up than
> commercial mobiles.  Some are really bad, at 200 msec or 
> more.  

My recommendation is to set ALL digis to 150 ms.  That is TXD =
15.
That is, assuming that the radio at THAT digi can handle it. 

And then test it against the 3 or so surrounding LOCAL DIGIS.

1) If it works with those local next-hop digs, then DONE.  Don't
worry about any other possible digis, because we don't care if
the packets hit them or not...

2) All Kenwood mobile receivers can receive as short as 100 ms.
SO all those mobile users out there will still SEE the out put
of this digi.

3) TRACKERs are a don't-care-situation, since they don't hear
anyway.

4) Home stations that cant see 150 ms packets, too bad.  They
are probably watching the internet anyway (grin)...  If their
radio is that slow, then they need to fix it if they want to see
the new-and-improved local APRS network..

De Wb4APR, Bob...