A radio wave is an electromagnetic wave propagated by an antenna. Radio waves have different frequencies. The listener can tune the radio receiver to a specific frequency to catch a specific radio signal. For example, all FM radio stations transmit in a band of frequencies between 88 megahertz (millions of cycles per second) and 108 megahertz, and any listener who tunes his radio receiver to a frequency falling in this range would have access to that specific FM radio station's programs. Common radio frequency bands include

• FM – 88 MHz to 108 MHz
• AM – 535 KHz to 1.7 MHz
• Citizen Band (CB) Radio – 26.96 MHz to 27.41 MHz
• Short Wave Radio – 5.9 MHz to 26.1 MHz.

Every radio setup consists of two parts, the Transmitter and the Receiver. The transmitter receives the message, encodes it onto a sine wave (a continuously varying electromagnetic wave) and transmits it with radio waves. The receiver receives the radio waves and decodes the message from the sine wave it received. The transmitter and the receiver use antennas to radiate and capture radio signals. The function of the antenna in a radio transmitter is to send radio waves into space, and in a radio receiver, it is to capture the transmitter's power to the maximum extent and route it to the tuner. The size of the antenna depends on the frequency of the signal to be transmitted or received.

A radio station transmits the sine waves, with information (programs) encoded on them, into space with help of an antenna. These sine waves are captured by antenna at the receiving station (radio set). The sine waves themselves do not contain any information and are modulated so as to hold information. Normally, sine waves are modulated in three ways:

• Pulse Modulation (PM): In PM, the sine wave is turned on and off at specific intervals. This is an easy way of sending coded messages. Usage of PM is comparatively less.
• Amplitude Modulation (AM): In AM, the amplitude of the sine waves (its peak to peak voltage) differs. AM is the most commonly used mode across the world.
• Frequency Modulation: In FM, the transmitter's sine wave frequency changes very slightly, based on the information signal. FM is largely immune to static (not useful or empty transmissions), which enhances the effectiveness of transmissions.

The sine waves with encoded messages are captured by antenna and sent to the tuner in the receiving station. The tuner's function is to separate one from the other, the thousands of sine waves received by the antenna. Tuners use the resonance principle, i.e. they resonate and amplify at one sine wave frequency, ignoring all other sine wave frequencies. They thus enable radio to receive only one sine wave frequency. The decoding of the information on sine waves in that particular frequency is done with the help of a demodulator or detector in the radio (detector defers from one radio type to the another). The radio amplifies this decoded information and sends it to the speakers (or headphone), from where the listener listens to the information (program).