In general, FM radio refers to radio that is broadcast using FM, or frequency modulation, as its modulation scheme. Frequency modulation is the shifting of the frequency of th
…e transmitted signal above and below an assigned "center frequency" or "carrier frequency" to impress the signal on the carrier. This modulation scheme is resistant to noise to a much greater degree than amplitude modulated (AM) signals. Sometimes we talk about FM radio as those broadcast frequencies between about 88 MHz and 108 MHz on the electromagnetic spectrum. This is often what the term means, but as FM is a way to put information on a carrier, that type of modulation could be used on just about any signal you'd care to apply it to. Certainly communications and amateur radio use it frequently on frequencies outside the so-called FM broadcast band. To make it simple there is an AC signal of fixed frequency and level at the transmitter and that is transmitted to the air. that is a carrier signal wich has no information but the radio station modulate this Carrier by an analog sound voice which makes the frequency change and a radio will detect this frequency change and extract back to analog signal regenerating the analog signal voice. (MORE) 
