What is FM Transmission?

            Over the year frequency modulated FM transmission has attained wide popularity due to its clarity and high fidelity in reproducing the broadcast speech or music. It can also provide a stereophonic effect to the sound produced at the receiving end. Before television came into our homes, radio was a popular entertainment medium. With FM transmission capturing the imagination of people, radio is likely to become popular once again.

FM Transmission Provider

            The earlier transmission services were basically amplitude modulated AM, which could not filter the noise and hence lacked the clarity that FM can provide. But what is the fundamental difference between AM and FM transmission?

            In both AM and FM transmission, radio waves are modulated by mounting it on the carrier frequency, which is essential for broadcasting and propagation. In AM transmission, the waves are constant in frequency but the amplitude varies, whereas in FM transmission, the amplitude is constant and the frequency varies. In simple terms, in AM amplitude is modulated and in FM, the frequency is modulated.

            Modulation is the process of coding the sound waves for transmission, and is done either by altering the amplitude of the wave or its frequency.

            We now need to understand three fundamental concepts- modulating wave, carrier wave and modulated wave. The modulating wave is the information bearing signal such as human voice or music, audible to the human ear, and intended to be communicated to a receiver. The carrier wave can be transmitted over long distances and is not audible to the human ear. The modulated wave is the wave derived by impressing the information bearing signal on the carrier wave. This wave is transmitted through space to the receiver.

            How is it that the FM transmission provides excellent reception?

            Speech itself is represented by an irregular wave pattern. An FM receiver has to detect frequency changes only; it does not reproduce any amplitude changes caused by electrical interferences. As a result, almost all background noise can be eliminated using filters, producing excellent reception.

            FM transmission is used in radio broadcasting services, multi-channel carrier telephones, communication satellite links, telegraphy, mobile communications, navigational and meteorological equipment as well as for medical diagnostic instrumentation. FM also exhibits channel grabbing that is, if two FM signals are available, the stronger of the two is received and the other is nearly excluded. This permits low-power radio stations operating in the same frequency to operate close to each other. AM transmission does not possess this ability.