The output of the IF amplifier is applied to the
detector, which recovers the information from the modulated
signal. To receive Morse code, most communications receivers incorporate a
beat-frequency oscillator (BFO) into the detector stage. The
BFO operates at 1 kHz or 400 Hz above or
below the last IF. Transitions in the RF carrier are
translated into transitions in the IF, which the BFO translates
into audible tones. The BFO is switched off during normal
voice reception to prevent interference.