PSK31 is a method of communicating by sending data over radio which was developed by Peter Martinez, G3PLX. It uses a very narrow band, phase modulated signal and special data encoding, to allow operators to "chat" in a manner similar to RTTY. However, PSK31 is much more effective than RTTY, being more resistant to interference and needing less power to achieve solid copy. I have made many satisfactory contacts using my Elecraft K2 generating just 5W pep output
Most PSK31 operators use PC software that generates and decodes the audio PSK signal using the computer sound card. The output from the radio receiver is fed into the sound card's line input socket and the software decodes it and displays the text on the screen. To create a PSK signal for transmitting the sound card generates the audio which is taken from the speaker socket and fed to the transceiver. With many transceivers (including the Elecraft K2) the audio must be connected to the microphone socket after some fairly heavy attenuation. Many desktop-style transceivers have a dedicated data interface which avoids the nuisance of disconnecting the mike whenever you want to operate on PSK.
Many programs are now available that enable you to send and receive PSK31. For more information about them visit the Official PSK31 WWW Homepage.
One interesting development for those who would like to write their own PSK31 software is the PSK31 Core DLL by Moe Wheatley, AE4JY, developer of WinPSK. The advantage of writing your own program is that you can make it look and work the way you want. However, the hard part for most people is writing the code to generate and decode the PSK31 signal using the sound card. The PSK31 Core DLL does that for you, leaving you with the job of creating the user interface. I worked with Moe to develop a demonstration of how to use the DLL in a Borland Delphi program called PSK31Test. To read about it and download a copy, click here.
If you haven't tried the PSK31 data mode yet (or if you're already QRV on the mode and are interested to see how well your signal is getting into Europe) check out one of the online PSK receivers. These tend to come and go, so unfortunately I can't provide any links, as they would be out of date in a few weeks.
The screen capture shown above was taken from an online PSK receiver in Germany. It was taken during DJ2CV's over, so his signal at the German receiving station is weak. But the text from me is received with 100% copy. Not bad for 5 watts to a loft antenna!