[aprssig] New PSK31 firmware for OpenTracker

[scott at opentrac.org]

I got inspired to work on the PSK31 code a bit tonight, and now instead of
the carrier being fixed at 500 hz, you can set it to any multiple of 31.25
hz, up to 7968 hz.  Directly connected to DigiPan, I've verified that it
works from 62.5 hz (sounds like a freight train) to 7 khz or more - beyond 6
khz, you're past the Nyquist frequency for DigiPan and it gets imaged.
Still, the imaged signal was at least partially copyable all the way to 7968
hz.  Yeah, there's no practical need for that, I just thought it was cool
that it actually worked that high.

Anyway, the important thing is that you can now run it on a
crystal-controlled rig like the Warbler and set your transmit frequency
through software.  You can also set different frequencies in each profile,
so you can switch using the jumper or any other switching parameter.

The tracker's output signal should be pretty clean.  I'd be interested in
getting some feedback on real-world IMD performance, though.

The firmware's available now, but it requires the latest version of the
configuration program.  Once you've got that, you can load the firmare with
the 'load firmware from web' button.

I've got to see if I can find my docs on the PropNet^31 checksum format, and
try to find room to implement that.  I've already disabled SmartBeaconing in
PSK31 mode - hopefully I won't have to take anything else out.

Scott, N1VG
http://n1vg.net/opentracker