when the transmission station radiates the radio waves, these are propogated through space and received by the radio receiver. the phenomenon is known as radio communication. thus the whole phenomenon can be divided into three parts viz. transmitter, transmission of radio waves and radio receiver.

1) TRANSMITTER
the function of producing raio waves for transmission into space is done by transmitter. it is very vital part of the broadcasting station. it consists of microphone, audio amplifiers, oscillator and modulator.
the figure shown below shows the general principles of radio broadcasting, transmission and reception.
1 --> A) MICROPHONE
It converts sound waves into electrical waves. when a soun is made, the varying air pressure on the microphone generates an audio electric signal corrosponding to the frequency of the original signal.
1 --> B) AUDIO AMPLIFIER
The weak audio signals from the microphone are made strong by amplification through cascaded audio amplifiers. the output signal is fed to the modulator for modulation.
1 --> C) OSCILLATOR
Oscillator produces a high frequency signal called a carrier wave. usually, crystal oscillators are used. radio frequency amplifier stages raise the power level of the carrier wave to a suffecient level (generally to several killowatts). the high power helps in transmitting the signal to long distances.
1 --> D) MODULATOR
The modulator receives the amplified audio signals and carrier wave so formed in the previous stages. here, the audio signal is superimposed on the carrier wave in a suitable manner. resultant wave is called modulated wave or radio wave and the process is called modulation. the process of modulation permits the transmission of audio signal at the carrier frequency. As the carrier frequency is very high, therefore the audio signal can be transmitted to large distances. the radio waves from the transmitter are fed into the transmitting antenna from where these are radiated into space.

2) TRANSMISSION OF RADIO WAVES
The radio waves are radiated in all directions by the transmitting antenna. these radio waves travel with the velocity of light i.e. 3*10(rais to power 8) m/sec. The radio waves are electromagnetic waves posses the same general properties. these are similar to light and heat wave except that they have longer wavelength. It is clear that radio waves are sent without employing any wire. It can be easily shown that at high frequency, electrical energy can be radiated into space.

3) RADIO RECEIVER
When the radio waves reach the receiving antenna it induces emf in it which is very small in magnitude and is fed to the radio receiver. Here, the radio waves are first amplified then the process of demodulation to extracts signal from them. the signal is amplified by audio amplifiers and then fed to the speaker for reproduction into sound waves.