English: Block diagram of a single conversion superheterodyne radio receiver . Invented by Edwin Armstrong in 1918 during World War 1, the superheterodyne is the design used in almost all modern radio receivers . The incoming radio signal from the antenna (left) is passed through an RF filter to attenuate some undesired signals, amplified in a radio frequency (RF) amplifier, and mixed with an unmodulated sine wave from a local oscillator . The result is a "beat" frequency or heterodyne at the difference between the input signal and local oscillator frequencies, a lower frequency called the intermediate frequency . The IF signal selected and strengthened by several IF stages that bandpass filter and amplify the signal. The IF signal is then applied to a demodulator that extracts the modulated audio signal. An audio amplifier further amplifies the signal, and the speaker makes it audible.

. Superheterodyne receiver block diagram.svg is identical to this image except it doesn't show the image rejection filter