[aprssig] Modems and FEC

Mon Feb 14 10:15:35 EST 2022

While I would like to see APRS "improve with age" I'm fully behind the 
"support the existing customer base" philosophy.  There should be a 
feeling of respect for the people that spent money and effort to use 
APRS in the field.

I have a handful of APRS systems I fly on model rockets.  And a couple 
of APRS capable handhelds.  I'd like those to stay reasonably relevant 
for a while.

And we should remember that "installed hardware" includes space based 
systems that have a big impact on public outreach for the hobby.  Having 
APRS and/or the voice repeater available on the ISS gives hams doing 
grass roots educational activity a reliable example of cool ham 
activity.  Changing out the ARISS APRS system on the ISS will not be 
easy or cheap.

Forming a non-profit to make sure APRS is supported and relevant sounds 
like a great idea.

But it seems like there should be a way to engage the manufacturing 
community into that organization.  While there are some "software only" 
APRS implementations I would be extremely sorry to see things like the 
TH-D74 and FT5DR, with embedded APRS support, go away.

Having a handheld radio with a complete, if minimal, tracking capability 
is invaluable in the field.  Extra boxes and the required harness will 
get caught up in bushes.
	73,
	Will

On 2/14/22 2:28 AM, Randy Hall wrote:
> Hey guys, I love the blue sky nature of this. Seriously. I use Direwolf 
> for a couple of big footprint digi/igate sites, and I'm hugely excited 
> about M17 as a data and digital voice mode.
> 
> But there is a ridiculous amount of installed hardware that only speaks 
> 1200 baud AX.25 AFSK packet, and it needs to be comprehended in whatever 
> vision we might create.
> 
> That isn't to say the physical layer definition shouldn't be expansive 
> to include and accommodate many different OTA modes. But physical layer 
> is just part of it.
> 
> As for OpenTrac, I tried visiting http://opentrac.net/ 
> <http://opentrac.net/> and was visited with a "site down" notification. 
> Is the site meant to be offline?
> 
> --R
> /--/
> /*Randy AA6RH*/
> /aa6rh at socorad.io <mailto:aa6rh at socorad.io>/
> /Grid Square: CM88pl/
> /QRZ Profile <https://www.qrz.com/db/aa6rh>
> /
> /Sonoma County DMR: BrandMeister 31707 
> <https://brandmeister.network/?page=lh&jsonquery=%7B%22condition%22%3A%22AND%22%2C%22rules%22%3A%5B%7B%22id%22%3A%22DestinationID%22%2C%22field%22%3A%22DestinationID%22%2C%22type%22%3A%22integer%22%2C%22input%22%3A%22text%22%2C%22operator%22%3A%22equal%22%2C%22value%22%3A%2231707%22%7D%5D%7D>/
> 
> 
> On Sun, Feb 13, 2022 at 9:28 PM Mobilinkd LLC <mobilinkd at gmail.com 
> <mailto:mobilinkd at gmail.com>> wrote:
> 
>     I helped define the M17 data modes, which includes a raw packet
>     mode.  M17 uses 4-FSK modulation with FEC.  There is experimental
>     firmware available for the Mobilinkd TNC3 and NucleoTNC that will do
>     M17 packet mode. I've had an M17 APRS repeater up at times in Chicago.
> 
>     Data modes on M17 approaches 5kbps throughput.  It uses 4800
>     symbols/sec, 9600bps, with a slightly punctured convolutional code.
> 
>     https://m17project.org/ <https://m17project.org/>
> 
>     Kind Regards,
> 
>     Rob Riggs WX9O
>     Mobilinkd LLC
> 
> 
>     On Sun, Feb 13, 2022 at 10:54 PM Gregg Wonderly <gregg at wonderly.org
>     <mailto:gregg at wonderly.org>> wrote:
> 
>         OpenTrac is an even better idea and more extensible and more
>         easily processed than APRS packets!  Let’s really take a moment
>         to reflect on what it could mean to start with a better solution
>         end to end!
> 
>         Gregg
> 
>         Sent from my iPhone
> 
>>         On Feb 13, 2022, at 6:32 PM, John Langner WB2OSZ
>>         <wb2osz at comcast.net <mailto:wb2osz at comcast.net>> wrote:
>>
>>         
>>
>>         __ __
>>
>>         The AX.25 and APRS protocol specifications say nothing____
>>
>>         at all about modems.____
>>
>>         __ __
>>
>>         The reason that we are using 1200 bps is because early ____
>>
>>         packet radio developers, in Canada, in the late 1970s,
>>         happened ____
>>
>>         to acquire a pile of old Bell 202 modems for 75 cents each.____
>>
>>         __ __
>>
>>         The method that we use for 9600 bps was developed in____
>>
>>         the late 1980s.  It has been widely implemented but won't____
>>
>>         work with the microphone and speaker connections because____
>>
>>         the audio processing distorts the signal and limits the
>>         bandwidth.____
>>
>>         __ __
>>
>>         In the early 1990s, multiple TNC vendors produced products
>>         capable____
>>
>>         of 2400 bps:  MFJ-2400, AEA PK232-2400, Kantronics KPC-2400.____
>>
>>         Maybe if other vendors had offered the same we would all be
>>         using____
>>
>>         2400 bps today.____
>>
>>         __ __
>>
>>         With the shift from hardware modems to software modems,____
>>
>>         the possibilities are endless.  Upgrades are easy. ____
>>
>>         __ __
>>
>>         __ __
>>
>>         Two methods of Forward Error Correction are currently being
>>         used:____
>>
>>         (1)FX.25 which is completely interoperable with original
>>         AX.25.____
>>
>>         (2)IL2P which has less overhead but is not compatible.____
>>
>>         __ __
>>
>>         __ __
>>
>>         Better alternatives are available today for those who want to
>>         use ____
>>
>>         them.   The problem is trying to convince most of the
>>         installed base____
>>
>>         to break free of a precedent set more than 40 years ago.____
>>
>>         __ __
>>
>>         73,____
>>
>>         John WB2OSZ____
>>
>>         __ __
>>

-- 
Will Marchant, KW4WZ
will at spaceflightsoftware.com
http://www.spaceflightsoftware.com/will/