The regenerative detector, invented by Edwin H. Armstrong in 1912 CE, is the simplest technology available for making unmodulated and on-off-keyed continuous-wave radio signals audible as sound by means of electronic frequency translation.

At base, a regenerative detector is merely an electronic radio-frequency oscillator into the feedback loop of which radio-frequency signals from an antenna are introduced, and from which audio resultants of heterodyning between the incoming signals and the oscillating detector's self-generated signal are extracted.

The preceding two one-sentence paragraphs fully describe the function of the regenerative detector as introduced by Armstrong for reception of on-off-keyed continuous wave (CW) signals. In that capacity, the regen (as later aficionados of the technique would dub it) revolutionized CW communication because it could render as usefully readable signals far weaker than competing means of CW reception could resolve.

With the advent of amplitude-modulated (AM) radiotelephone, soon harnessed for AM broadcasting, it was found that just below the threshold of oscillation a regenerative detector could, by virtue of the high RF amplification afforded by positive feedback working in conjunction with rectification by the grid-cathode diode inherent in the vacuum tube, work similar magic in the rendering into audio of AM signals carrying voice and music. In this scenario, the AM-signal carrier, not the detector, provides the heterodyning energy necessary to translate the signal's information-bearing sidebands back to their original audio form.