rpitx_alsa

An ALSA sound driver interface for sending samples to F5OEO's rpitx. This is only a proof-of-concept demo. It should work, but it is in no way complete and/or perfect.

How does it work

This program is comprised of a kernel module, whose job is to collect the audio data from whichever amateur radio program you want to use, and a daemon, whose job is to call librpitx to transmit it. Internally, they communicate through the /dev/rpitxin character device.

Compile and install

First, I assume you have already tried the "regular" rpitx and everything has been configured properly on your Pi. I.e., follow all the instructions of rpitx first: https://github.com/F5OEO/rpitx.

Then, you need to clone this repository. Since it depends on the F5OEO's "librpitx" repository, you need to run:

$ git clone --recursive https://github.com/felixzero/rpitx_alsa.git

Then you need to build the kernel module (the ALSA driver). You need the kernel headers and of course, gcc. But you need to make sure your system is up-to-date first, otherwise the build will fail. Run:

sudo apt update
sudo apt upgrade

And reboot if any significant update was done. Then, run:

$ sudo apt install raspberrypi-kernel-headers

Then:

$ cd rpitx_alsa/
$ cd kernel_module/
$ make

If there are no error, you can now compile librpitx and the daemon:

$ cd ../daemon/librpitx/src/
$ make
$ cd ../..
$ make

If there are no errors, you are done!

Run

To be able to use the transmitter, you must first load the kernel module. In the kernel_module folder, just run:

$ sudo insmod snd-rpitx.ko

Then, go up one folder ($ cd ..), and run the daemon in background, still as root:

$ sudo ./rpitxd &

Now, you are all set, you can configure your favorite amateur radio software (Quisk, fldigi, WSJT-X, QSSB...) to send data to one of the following sound devices:

• hw:rpitx,0 for software producing stereo I/Q data (for instance Quisk or all SDR software)
• hw:rpitx,1 for software producing mono SSB data (most digimode programs). The sound driver will generate the adequate Q data, assuming the original sound is USB.

You can also dynamically tune the frequency and harmonics of rpitx by writing to:

$ sudo su -c "echo 14070000 > /sys/devices/rpitx/frequency"
$ sudo su -c "echo 1 > /sys/devices/rpitx/harmonic"

Have fun!