In a radio receiver, a beat frequency oscillator or BFO , is a dedicated oscillator used to create an audio frequency signal from Morse code radiotelegraphy (CW) transmissions to make them audible. The signal from the BFO is mixed with the intermediate frequency signal to create a heterodyne or beat frequency which is heard as a tone in the speaker. BFOs are also used to demodulate single-sideband (SSB) signals, making them intelligible, by essentially replacing the suppressed carrier. BFOs are usually included in communications receivers designed for short wave listeners and amateur radio stations, which often receive CW and SSB signals.