[aprssig] More efficient use of channel capicity throughshorterpackets

Joel Maslak jmaslak-aprs at antelope.net
Thu Oct 12 18:44:18 CDT 2006

On Oct 12, 2006, at 5:15 PM, Robert Bruninga wrote:

> My recommendation is to set ALL digis to 150 ms.  That is TXD =
> 15.

I think that is too long.  I think 100 ms is plenty if your TX radio  
will do it.

The reason is most stations that care about decoding packets run open  
squelch.  So squelch gate time isn't an issue.  The D700s/D7s who's  
problems seem to define the entire network and hold it to the common  
denominator still will work even with squelch used.  Anything other  
than a D700/D7 that decodes packet should run OPEN SQUELCH.  If it  
can't lock onto a tone in a tenth of a second, it's never going to  
pickup the 1200 transitions per second once the data starts coming.

> That is, assuming that the radio at THAT digi can handle it.

If it can't, it's time to look at fixing that problem.  I've even  
used cheap non-data Alinco mobile rigs with < 100ms TX delay, so  
*something* should be on the used market that will work fine.  1200  
BPS packet isn't too picky on radio.

> 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..

Even the slowest radio can decode this.  It's not a radio speed issue  
on the RX end if you run squelch open, as is recommended for packet.   
Even sound card packet should be able to handle open squelch, so home  
stations don't really have an excuse at all.

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