Amateur radio enthusiasts have been at the forefront of experimentation and development since the very earliest days of radio. All over the world, radio amateurs use a wide range of modes and frequencies to communicate. When surplus teleprinters became available in the early 1950s, radio amateurs adapted them for their own use and the first modern digital mode was born. Half a century later, RTTY is still widely used, and has been joined by a great number of other modes.
Most software for digital modes use a soundcard to communicate with the radio, and a simple circuit to switch the radio to transmit. Examples of the PTT circuits used may be found on Tom Sailer's soundmodem pages.
In order to transmit data over the air, you will need a suitable licence. In many countries you can get licence-exempt radios, but it may not be legal to use them for data modes. It is also possible to connect two PCs together via audio cables, and experiment with data modes.
Most of the Linux Amateur Radio AX.25 HOWTO is relevant here. Install the libax25, ax25-apps and ax25-tools applications as appropriate from AUR.
For AX.25-based modes (packet radio, and APRS), Tom Sailer's soundmodem software will allow you to transfer data at up to 9600 baud, with a suitable radio. APRS uses 1200 baud data, which can be passed over the microphone and loudspeaker connections. High speed modes like G3RUH require specially-adapted radios, because the wide band data needs to have a flat audio response.
Soundmodem can be used as a KISS modem, which is treated as a serial device, or as an AX.25 network device which may be shared by several applications.
If you want to use soundmodem as an MKISS network device, you'll need to rebuild your kernel and install the mkiss kernel modules.
Run soundmodem as root:
If you have configured soundmodem as a KISS modem, you will need to set the device to be user-readable:
# chmod 666 /dev/soundmodem0
WSJT stands for "Weak Signal Communication by K1JT". WSJT was developed by Nobel Prize winning physicist Joe Taylor, who has the amateur radio callsign K1JT. The software offers offers a rich variety of features, including specific digital protocols optimized for meteor scatter, ionospheric scatter, and EME (moonbounce) at VHF/UHF, as well as HF skywave propagation. The program can decode fraction-of-a-second signals reflected from ionized meteor trails and steady signals 10 dB below the audible threshold.
WSJT is in ongoing, active development by a team of programmers led by K1JT. The latest verion of the software can be retrieved and built from the svn repository at berlios.de using wsjt-svn in the AUR. WSJT (and the related program WSPR) have the option of being configured with
If you build with one and experience problems, edit PKGBUILD to try the other.
WSPR (pronounced whisper) is a Weak Signal Propagation Reporter. It was introduced in 2008 by K1JT following the success and widespread adoption of WSJT by the amateur radio community. WSPR enables the probing of propagation paths on the amateur radio bands using low power transmissions. Stations with Internet access can automatically upload their reception reports to a central database called WSPRnet, which includes a mapping facility. The package wspr-svn in the AUR builds the current version of the program from the svn repository.
Xastir stands for X Amateur Station and Information Reporting. It works with APRS, an amateur radio-based system for real time tactical digital communications. Xastir is an open-source program that provides full-featured, client-side access to APRS. It is currently in a state of active development. Arch users can install the bleeding-edge version of Xastir from the CVS repository on Sourceforge with xastir-cvs in the AUR.
Xastir is highly flexible and there are a wide variety of ways it can be configured. For example, it can be evaluated without radio hardware if an Internet connection is available. It can be optionally built with one of the many Festival speech synthesis packages in the AUR. The wiki at xastir.org is very thorough and gives excellent information on its range of capabilities and setup.