ABSTRACT
This chapter discusses the presently available technology in communication, search and rescue operations. Heinrich Hertz conducted experiment in 1887 and proved the existence of electromagnetic waves and showed that these waves propagate in vacuum and can be stopped by a metallic screen. Radio waves are produced by changing fields in alternating current (AC). The magnetic field propagates at right angle to the electric field. The wave is polarised in the direction of the electric field. The propagation of an alternating electromagnetic field in space constitutes electromagnetic waves. Radio broadcasting in transmission of speach, music, telegraphic signals by means of radio. Radio communications are the transmission of modulated electromagnetic waves by the radio transmitter and their demodulation in a radio receiver. The alteration or change of parameters of electromagnetic waves is called modulation. The wave which is modulated is called carrier wave and its frequency is called carrier frequency.
