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Radio is the the wireless transmission of signals by modulation of  electromagnetic waves of a range of  frequencies, which travel through air or vacuum of space. Through the term radio is commonly used to refer to broadcast radio, wireless signals are also used for mobile communication, Wi Fi and bluetooth.

AM radio works on the principle of  amplitude modulation, and the amplitude of  the transmitted signal is proportional to amplitude of the sound signal which is being broadcast. The AM radio signals are broadcast in the Medium Frequency (0.300 MHz to 3 MHz) radio spectrum.  The maximum strength of  the signal from AM radio stations is 50,000 W.  AM radio signals are affected by static, lightning and other sources of  interference since the amplitude of the transmitted signal is modified.

Compared to AM radio, voice and audio broadcasts on FM (Frequency modulation) radio are more clear. The frequency of  the broadcast signal is modulated according to the amplitude of the sound signal.  Since the frequency is modulated, static and interference have little effect on the quality of  the sound signal. FM signals are transmitted at  the Very High Frequency (VHF ) range of the radio spectrum - 30 MHz  to 300 MHz . However, the FM  signals are available over a limited range , usually less than 250 km around the transmission tower.