Chapter 9 / 9.2 / 9.2.6

9.2.6 Detector Stage

The detector recovers the modulating signal from the IF. For AM, a diode envelope detector suffices; for FM, a discriminator or phase-locked loop detector is used. Digital demodulators now perform the equivalent operation mathematically in DSP.

To receive Morse (CW) or SSB signals, a beat-frequency oscillator (BFO) is injected at a small offset (typically 400–1,000 Hz) from the IF, producing an audible tone. The BFO is disabled for normal voice or broadcast reception.