[aprssig] Modems and FEC

Gregg Wonderly gregg at wonderly.org
Sun Feb 13 23:53:00 EST 2022

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!


Sent from my iPhone

> On Feb 13, 2022, at 6:32 PM, John Langner WB2OSZ <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
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