Yes, Soundcard packet/aprs for the Pi

I have used soundcard software for several years on my Windows-based computers, as it gives me the greatest flexibility and has actually been pretty cost effective.  Even if I buy a dedicated USB soundcard dongle, the cost is typically less than $10.  Since many new radios already have VOX operation built in, I don't need to go to the higher cost of a com port keying circuit or something like the Signalink USB.

I've always wanted to do APRS on a Raspberry Pi.  It's low power consumption plus low cost makes it an excellent solution.  Most dedicated trackers run $50-100 depending on features.  I think the KPC-3 from Kantronics is still over $100 new.

Raspberry Pi is $40.  Add a USB sound dongle at $8 and you can see how it is very attractive financially.  Not to mention the ability to interface something like the Arduino to it for telemetry work.  Write something in Python or C and you have a very customizable box.

The main barrier to running packet/APRS on a Raspberry Pi has been the lack of good experience with sound card modems on it.  Conventional wisdom has been that it doesn't have enough horsepower to handle the DSP routines required to decode packet and other modes (like PSK31, etc.)

Step one was getting a USB soundcard.  Courtesy of Amazon, I was able to  buy a unit pictured below:

 



Step two was connecting it to the Pi through my USB hub with an ancient Radio Shack scanner tuned to 144.39 (APRS frequency).  Audio output from the scanner was connected to the Mic input line on the sound card dongle.

Last step was downloading the Dire Wolf sound card program and installing it.  Once I got the alsamixer settings correct for the microphone gain, APRS packets from my local station at house started streaming across the screen (pardon me for the light green text that is hard to read):

I'll need to make up some more cables to tie to a Baofeng transciever.  The Dire Wolf software provides a KISS port on 8001 for most of the popular APRS packages like APRS-IS, Xastir, BPQ32 etc. to use, so that makes it super convenient.

I've been reading about the ability of the Raspberry Pi to generate up to 200 Mhz signals using PWM on the GPIO pins.  With a mixer, good filtering section, and a decent amplifier section, maybe the Pi becomes its own transmitter and receiver.  Sounds like a good idea for a TDRC "We make it better" project......