Beat frequency oscillator
![Separate BFO oscillators were manufactured for receivers that didn't have them; a Rohde und Schwarz STI4032 from 1944.](/Images/godic/202412/23/D_1944_Rohde_und_Schwarz_STT4032_Front_Large2620.jpg")
![One of the first crude examples of a BFO, the Goldschmidt tone wheel. Before vacuum tube oscillators were invented, the first CW receivers used a wheel with electrical contacts around its rim, spun at a high speed by a motor, to interrupt a current to create a radio frequency signal to beat with the incoming radio signal. This example, at the Tuckerton transatlantic receiving station in New Jersey in 1917, created a 40 kHz signal.](/Images/godic/202412/23/Goldschmidt_tone_wheel2620.jpg")
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.