fibres in wireline communication and free space in wireless communication. vi) Receiver The signals that are transmitted through the communication medium are received by a receiving antenna which converts EM waves into RF signals and are fed into the receiver. The receiver consists of electronic circuits like demodulator, amplifier etc. The demodulator extracts the baseband signal from the modulated signal.
Then the baseband signal is amplified using amplifier. Finally, it is fed to the output transducer. vii) Repeaters Repeaters are used to increase the range or distance through which the signals are sent. It is a combination of transmitter and receiver.
The signals are received, amplified and - - - - - - - - Unit electronics and Communication signals such as voice, music, picture etc are transmitted is known as bandwidth. If ν and ν are the lower and upper-frequency limits of a signal, then the bandwidth, BW = ν – ν . v) Bandwidth of transmission system The range of frequencies required to transmit a piece of specified information in a particular channel is called channel bandwidth or the bandwidth of the transmission system. .
PROPAGATION OF ELECTROMAGNETIC WAVES The electromagnetic wave transmitted by the transmitter travels in three different modes to reach the receiver according to its frequency range. They are • Ground wave propagation (or) surface wave propagation (nearly kHz to MHz) • Sky wave propagation (or) ionospheric propagation (nearly MHz to MHz) • Space wave propagation (nearly MHz to GHz) i) Ground wave propagation If the electromagnetic waves transmitted by the transmitter glide over the surface of the Earth to reach the receiver, then the propagation is called ground wave propagation. The corresponding waves are called ground waves or surface waves. The pictorial representation is shown in Figure .
(a). Here both transmitting and receiving antennas must be close to the Earth's surface. It is mainly used in local broadcasting, radio navigation, for ship-to-ship, ship- to-shore communication and mobile communication. ii) Sky wave propagation The mode of propagation in which the electromagnetic