An interesting post on the Southgate ARS blog today about FreeDV, a free to download and use digital modulation system than needs less than half the bandwidth of conventional SSB. It needs audio processing with a PC on both RX and TX. The article includes the quick start guide for set-up and a clip of a QSO using the mode on 14MHz with 25W. Speech quality sounds excellent.
More information at the FreeDV homepage http://freedv.org/tiki-index.php. An important point to note is that the codec and modem are both open source, patent free so anyone can experiment with them and modify them.
At the moment activity is centred on 14.236 MHz.