General Principles of Radio Broadcasting, Transmission and Reception

Radio communication is the radiation of radio waves by the transmitting station, the propagation of these waves through the space and their reception by the radio receiver.

The figure above shows the general principles of radio broadcasting, transmission and reception. We can divide the entire arrangement into 3 major sections, namely:

1. Transmitter
2. Transmission of radio waves
3. Radio receiver

Transmitter

This equipment is housed in the broadcasting station. It produces the radio waves for transmission into the space. The transmitter is made up of several components like:

Microphone – This is a device that converts soundwaves into electrical waves. When the speaker speaks or a musical instrument is played, the varying air pressure on the microphone generates an audio electrical signal that corresponds in frequency to the original signal. The output of the microphone is fed to a multistage audio amplifier that raises the strength of this weak signal.

Audio amplifier – The audio signal from the microphone is usually quite weak and requires amplification. This is accompanied by cascaded audio amplifiers. The amplified output from the last audio amplifier is fed to the modulator for rendering the process of modulation.

Oscillators – The purpose of the oscillator is to produce a high frequency signal, called a carrier wave. Normally, a crystal oscillator is used for this purpose. The power level of the carrier wave is raised to a sufficient level by radio frequency amplifier stages. Most of the broadcasting stations have a carrier wave power of several kilowatts. Such high power is required for transmitting the signal over long distances.

Modulator – The amplified audio signals and carrier wave are fed to the modulator. In the modulator the audio signal is superimposed on the carrier wave in a suitable manner. The resultant waves are called modulated waves or radio waves and the process is called modulation. The process of modulation allows the transmission of audio signal at the carrier frequency. Since the carrier frequency is very high, the audio signal can be transmitted to large distances. The radio waves from the transmitter are fed to the transmitting antenna or aerial from where they are then radiated into the space.

Transmission of Radio Waves

The transmitting antenna radiates the radio waves in space in all directions. These radio waves travel with velocity of light that is 3 x 10⁸ m/sec. The radio waves are electromagnetic waves and possess the same general properties. These are similar to light and heat waves except that they have longer wavelength.

Radio Receiver

On reaching the receiver antenna, the radio waves induce tiny e.m.f in it. This small voltage is fed to the radio receiver. Here, the radio waves are first amplified and then the signal is extracted from them by the process of demodulation. The signal is amplified by audio amplifies and then fed to the speaker for reproduction into sound waves.

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