This is a sketch of some of the components involved in an AM radio receiver. A typical AM radio can be tuned to receive the output of any AM radio transmitter which is close enough to provide adequate signal strength.

The information signal as a low frequency 'audio" signal is superimposed upon a much higher radio frequency 'carrier' which can be transmitted and then received by the radio antenna. However, the antenna will receive the signal from all AM radio transmitters in the area simultaneously, and you would usually want to listen to just one. Therefore in the development of practical radio, it was necessary to develop a way to tune precisely to one carrier and reject all the others. Each radio station is assigned a precise carrier frequency and it must keep its transmitted information within +/- 5 kHz of that carrier frequency.

The scheme developed to make AM radio a practical means for mass communication was called "heterodyning". It involves using a local oscillator in the receiver that tunes along with the input radio frequency amplifier so that their difference or beat frequency remains the same. This beat frequency is called the "intermediate frequency" or IF, and for the United States that beat frequency is 455 kHz. After initial amplification, the radio frequency (RF) signal is mixed with the local oscillator frequency to produce the IF, and all the subsequent stages are tuned to 455 kHz. The IF carries any AM signal that was on the original RF. This process has the practical advantages of allowing a high quality tuned RF amplifier on the front end to tune to the different stations, and then a high quality single amplifier and detector chain tuned to the single IF of 455 kHz.

After the Mixer, the frequency f_{Local Oscillator} - f_Carrier = 455kHz is amplified and then enters the detector stage. There it is rectified and fed into an AM detector circuit. This process amounts to a kind of filter that does not respond to the high frequency variations of the IF, but tracks the low audio frequency "envelope" of the IF signal. This gives an audio frequency output signal which is then amplified and supplied to a loudspeaker to convert it back into sound waves. That sound output is hopefully a faithful reproduction of the original input sound.

As a historical note, the reason for choosing 1480 kHz as an example AM frequency out of the range of 535kHz to 1605 kHz was that on one occasion when we were discussing AM radio, we were having a hard time eliminating a 1480kHz signal from some of our electronic equipment in the Department of Physics and Astronomy. For some reason, our whole building seemed to be an effective antenna for that particular radio station. With the help of the engineers from the station and some detective work on our own, we were able to solve the problem.