Packet radio is a means of sending data wirelessly over radio channels, and is often used by Amateur Radio Operators. (One form is APRS, described in our earlier post.) In the video following the break you get some idea of how packet radio communications are conducted. The video uses a piece of hardware known as a Terminal Node Controller (TNC) connected between an amateur 2-meter FM transceiver and a computer running a simple terminal program. The over the air protocol used is known as AX.25.
The Radio Shield by Argent Data Systems is an add-on kit for the Arduino development board that provides AX.25 packet radio send and receive capability, a prototyping area, and an HD44780-compatible LCD interface.Packets are sent and received in AX.25 UI frames. This allows operation on the APRS network. Unfortunately, it is not clear that this device is open source. While a schematic is provided, the ID of the U3 chip is omitted. Also, no source code has been released.
UPDATE: Argent has confirmed that U3 is a Freescale MC908JL16CSPE, states they haven’t had a chance to publish the source code yet.