[aprssig] 9600 APRS
wes at ai4px.com
Mon Feb 28 07:09:25 EST 2011
Perhaps because ham gear uses one local oscillator that has to shift frequency upon TX? Do the AIS units run two local oscillators? All ham gear now uses PIN diodes, so the problem isn't there.
I'm very interested in the self organizing nature of the AIS slots, but can't find any techhie info on it other than it works. Any tips for detailed info?
----- Original Message -----
From: Derek Love
To: 'TAPR APRS Mailing List'
Sent: Monday, February 28, 2011 6:10 AM
Subject: Re: [aprssig] 9600 APRS
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
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> wrote:
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 restrictions.
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