Frequency Modulation is a system of radio transmission which involves the modification of the rate of oscillation of the audio signal, before it is superimposed on the carrier wave in order for it to be sent via the antenna. This is distinct from the Amplitude modulation (AM), hence AM and FM waves may not be received at the same time. The first time FM was used was in 1936 by American inventor Edwin Armstrong. In 1961, the FCC authorised FM broadcasting. Thus FM channels grew in popularity.
Operation of FM broadcasting
As explained above, the frequency of an audio signal is modified before it is superimposed onto a carrier wave generated by the transmitter’s oscillator. The superimposition, just as in amplitude modulated waves, may take place after both the audio and carrier waves are amplified independently. In another method, the audio and carrier signals may be superimposed, and then amplified before being sent to the antenna. The advantage of FM broadcasting is that it is not affected by electrical disturbances, such as those caused by thunderstorms and automobile ignitions, unlike the case of AM broadcasting.
Applications of FM radio
FM receivers, if well designed, are not sensitive to electrical disturbances, thus making FM broadcasting popular for short range transmissions. FM can be broadcast over high-frequency bands where disturbances with AM bands are severe. To avoid mutual interference between stations operating at the same assigned frequencies between 88 and 108 MHz, the range of transmission using FM is limited. This allows FM broadcasters to be located within a few hundred kilometres of each other.