question_answer

Name the three different modes of propagation of electromagnetic waves. Explain, using a proper diagram the mode of propagation used in the frequency range from a few MHz to\[\mathbf{40}\text{ }\mathbf{MHz}\]. Or Mention three different modes of propagation used in communication system. Explain with the help of a diagram how long distance communication can be achieved by ionospheric reflection of radio waves.                

Answer:

                The different modes of propagation of e. m. waves are: (i) Ground wave propagation (ii) Space wave propagation (Hi) Sky wave propagation Sky wave propagation is used for the transmission of e. m. waves having frequency range from a few MHz to\[\text{4}0\text{ MHz}\]. As shown in the figure, here a radiowave is directed towards the sky and is reflected by the ionosphere towards the desired location of the earth.