Aside from a standard radio transceiver and a computer with a sound card, very little equipment is required to use PSK31. Normally, an older computer and a few cables will suffice, and many PSK31 software applications are free. Many operators now use a commercially available interface/modem device (or "nomic") between their computers and radios. These devices incorporate the necessary impedance matching and sound level adjustment to permit the sound card output to be injected into the microphone input, send the radio's audio output to the sound card input, and handle the radio's transmit-receive switching.