[aprssig] 9600 APRS

Derek Love DLove at app-tech.co.uk
Mon Feb 28 06:10:17 EST 2011

I've been looking at 9600 operation for a while, and it concerns me that
the spectrum efficiency is so poor; with 150ms TxDelays being used to
send a 35ms packet of data seems to be utterly ridiculous. I've been
working on marine AIS systems for nearly 10 years, and while I admit
that its design could be significantly improved, at least it only needs
26ms to send a total of 168bits of data - the Txdelay being essentially
24bits of preamble before the start flag (about 3ms) plus the 8 bits of
PA ramp timing (1ms). Why is there an order of magnitude difference in
the two systems which are otherwise, very similar?

Derek Love, Applied Technology UK 
+44 1749 881130 

-----Original Message-----
From: Wes Johnston, AI4PX [mailto:wes at ai4px.com]
Sent: 28 February 2011 01:42
To: ml41782; TAPR APRS Mailing List
Subject: Re: [aprssig] 9600 APRS

Yes, many new rigs are 9k6 ready, but they still have horrendous
txdelays.  Kantronics did make a good little dataradio years ago that
had something on the order of 40ms (???) txdelay.    And we can really
appreciate 9k6 for longer TCP type packets... packets >200 bytes.  But
for our little onsie twosie packets of 30 to 50 bytes, it's just not
worth the effort.
Moving an aprs digipeater to 440 would be great, 1200 baud sure.  What
would be cool would be to have 144.39 and a 70cm frequency bridged at
1200 so that it didn't matter which freq you used, you'd see everything
on your local digi on either frequency.  The purpose of this would be to
allow mobiles to run 70cm when they used 2m voice or vice versa.
Skipping right along, on Bob's random text files from years ago, one
really stuck with me.  It was running data output on the input frequency
of a repeater.  This would be prefect for 9k6 distribution of weather
products.  Thing is that today many voice repeaters have COR gated PL
tone outputs.  So we could transmit 9k6 on the output of the repeater
with no PL tone for HOURS.  Think of all the time that a given repeater
is inactive thru the day.  Of course once a voice user started on the
repeater, the data would pause.  Now if the voice users run PL tone
decoders, they'd never know it was there!  If they didn't run PL decode,
they'd hear quiet static, not annoying BRAAAAPPPPS.  Now what data would
you put on that?

"Language shapes the way we think, and determines what we can think
about." -- B. L. Whorf

On Sun, Feb 27, 2011 at 09:30, ml41782 < ml41782 at yahoo.com
<mailto:ml41782 at yahoo.com> > wrote:

Original MSG 
This is a savings of 27ms. based on his numbers. I have seen numbers
shorter and longer than 150ms for keyup. This doesn't sound like alot of
savings but every little bit helps.
9600 on VHF ?  I have never really seen this work on even on packet

I have seen 2400 & 4800 on VHF but a true 9600 no because of bandwidth

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