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
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Chetvorno