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[aprssig] 9600 APRS

Bob Bruninga bruninga at usna.edu
Thu Apr 2 04:03:50 UTC 2009


> My increasing involvement in Emergency Management...
> has gotten me back into APRS with a vengeance,
> and my Kenwood rigs are running hot.

I hope that doesn't mean you are flooding the channel with 1 minute position rates 24/7...

> The newer rigs will run 9600 APRS, 
> but there is no 9600 network for them.

Actually all of the APRS rigs going back to he introduction of the D7 in 1998 will run APRS at 9600.

> ... the capacity of the channel is as much 
> as eight times that of 144.39 because of 
> the speed increase. 

Unfortunately, I think it has been shown that the effective throughput will only about double because there is fixed overhead.  But your idea to bundle packets is a very good way to improve throughput... BUT...

But a lot of the value of APRS in the mobile is seeing the new info from the latest packet flash on your screen without having to move your fingers or hands from the wheel and without having to do anything.  This flash of info lasts 10 seconds whcih is about right for a 1200 baud channel operating at the Aloha limit.

If you fire-hose the channel with  4 times the data throughput (by bundling and going to 9600 baud), then only one of every 4 stations will get flashed on the mobile's screen, and the other 3 will not be seen.  Personally, I'd rather see everyone around me reliably, than 4 times as much spam from out of area that is hidden from view that I have to go look for, by searching through the lists of captured packets.

Again, your idea of bundling to improve throughput has merrit.  Ive looked for applications of it for years....  but if you acccept the fact that APRS is supposed to be a real-time information distribution and display system for mobiles, then it should only be applied to info that no one needs to see in real time.  And if local real-time info is in that category of no worth looking at, then why is it being transmitted on the local info channel?

About the only thing that fits this category is MESSAGES, since they will flash special alerts when they come in anyway to the recepient only, and those that are not addressed will not see them.  So they can be dumped at a high rate without any disadvantages...  But the problem there is, that there are too many trackers driving around and hardly anyone is messaging.  SO messaging remains a very small piece of APRS.

Though I think it could revolutionize amateur radio if we would just tie all of the dozens of amateur radio text messaging systems into APRS seamlessly.  See

www.aprs.org/aprs-messaging.html

Now that would be worth doing!  Both BUNDLING and 9600 baud!

Bob, WB4APR

>   We have better features built into the Kenwood
>   radios than we actually get to use because the
>   network at 144.39 is still 1200, hence very little
>   9600 ops- mostly satellite spotting. Since we allow
>   these features to languish unused or at least under
>   used, no other radio manufacturers seem to feel the
>   need to incorporate them in their product lines. Now
>   we have lost the TH-D7s. ( I don't really believe
>   that decision was made because of toxic chemicals in
>   the PCBs... Do you?)
>
>   How about something a bit different? Suppose, as an
>   experiment, here in Central NJ where there is a
>   pretty dense signal cluster, we were to set up a 440
>   UHF 9600 APRS digi at as high a point as we can get,
>   running as much power as we can manage.
>
>   Instead of having a conventional digi, have a
>   computer hooked to 2 radios/TNCs, one running at
>   1200 on 144.39, the other at 9600 on 440 UHF. Have
>   the computer APRS application record all the
>   received packets over a three minute period of
>   monitoring 144.39 1200 operations, compile them into
>   one long data stream and at the end of that 3rd
>   minute transmit that three minute take from 144.39
>   1200 onto the 440 UHF band 9600 channel in one long
>   burst. In the intervening minutes between that
>   digi-burst and the next, 9600 UHF APRS units can
>   transmit position packets, which will not be
>   digipeated immediately but will be scooped up by the
>   computer and incorporated into the next data burst,
>   and can be cross banded to 144.39 at 1200 as well.
>
>   If I am correct, this will cut packet collisions way
>   down, and on the UHF 9600 channel the air will be
>   clear, allowing for greater distance RX and TX in
>   between digi-bursts, at least until a large number
>   of people start running APRS at 9600 on UHF and we
>   eventually get QRM. And even if a large number of
>   people eventually do run 9600 on UHF, the capacity
>   of the channel is as much as eight times that of
>   144.39 because of the speed increase. That gives us
>   room for more content, larger packets, longer
>   messages, in short- More room to play with.
>
>   I am not a programmer, and so I can't make this
>   happen by myself. All I have is some money for
>   equipment and the desire to see this happen. One of
>   the talented APRS programmers out there would have
>   to get interested in this. Any takers?
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