[aprssig] OpenTracker PSK31 firmware released

[Scott Miller]

Ok, I finally got around to cleaning up the PSK31 code for release.  It's
available for download now at http://n1vg.net/opentracker/downloads.php.
Download the otwincfg-beta.exe configuration program first - it's got some
changes to handle the PSK31 configuration, plus some tweaks that *should*
fix most of the problems with USB serial adapters.

Once you've got the configuration program, you can use the 'web' button to
download the new firmware.  Due to space constraints, the PSK31 code doesn't
support SmartBeaconing or Base91 compressed format.  I'd like to have
compressed format as an option, but with the varicode encoding I'm not
entirely sure it'll be much shorter.  I'll have to do some testing.

The TXD parameter is in bytes rather than milliseconds for the PSK31 code -
it just sends the specified number of zeros before it starts sending data.
I've been using 20 for testing, which seems to be enough for DigiPan to lock
on.  Also, there's no path support - the transmission simply starts with
your callsign followed by >APRS:.  The carrier frequency is fixed at 500 hz
- that may be configurable in the future, but it's not a trivial change due
to the way the timing is set up.

There's no support for PropNet-style checksums yet.  I may tackle that soon,
but at the moment I have nothing installed that'll verify the checksums and
let me know if I got it right.

Other than the above mentioned limitations, everything else should work,
including telemetry reports.  I haven't implemented PSK31 for the weather
firmware yet, but if there's any interest I can do that.

Scott
N1VG