RADIO (PART 1)

 

We have discussed the topic “Television” that the modified form of the television. In television we hear the sound and as well as we also see the picture of the object. Basically in television video and radio signals modulated and demodulated separately and we can hear the voice with the help of loudspeaker and see the picture with help of screen. We can say that Television is modified form of the radio. Radio is only having sound so it is a simplified than television.

For the transmission of Radio and television the broadcasting station are established. At the broadcasting side of radio signals are modulated on with AM or FM and then these are transmitted with the help of transmitting antenna. On the other end receiver antenna of a radio receives the transmitted signal which is transmitted by transmitting antenna at the broadcasting station. After receiving the signal they enter in to the receiver and signals are separated from the carrier wave and we can hear the voice with the help of radio speaker.

 

Broadcast Station

Microphone, in the broadcasting studio is used to convert our audio in to the electric current before the signal is modulated in broadcasting unit. The microphone contains some form of mechanical device, such as a metal ribbon or coil or a crystal, which vibrates to convert the sound waves into an electric current. The current varies at the same rate or frequency as the original sound.

Electric current is said to be at an audio frequency. It is fed through an audio frequency amplifier, which increases its strength and then combined with carrier signal that is at a higher, radio-frequency. The carrier signals is altered or modulated by the audio-frequency signal.

 The modulated carrier signals are fed to the transmitting aerial. There electric currents cause radio waves to be emitted in all directions. The waves travel with the speed of light (that is about 300 million meters a second or 1080 million km/h). When they hit a receiving aerial, they set up oscillating waves in it, similar to those in the transmitting aerial.

 

Radio Reception

 

At the receiver end when signals are received are very weak and so when the radio receiving set is ‘tuned’ to receive them, they are fed into a radio frequency amplifier to be strengthened. Then they are passed to a detector which separates the audio frequency signal from the carrier wave.

There now remain patterns of currents identical to those that left the microphone in the broadcasting studio. They are amplified as necessary by an audio frequency amplifier and fed to a loudspeaker. The loudspeaker acts like a microphone in reverse. The electric currents flow in an electromagnet to make a diaphragm move backwards and forwards to set up sound waves in the air. These sound waves are as near as possible the same as those waves that originally struck the microphone.

That was about the radio transmission and reception. In the next lecture we will discuss about the AM, FM transmission and also the ionosphere.