Sound waves
are produced by the source, a microphone turns the sound waves into an
electrical signal. the sound waves cause an electric current that runs through
the microphone to vary, these variation form audio frequency waves. The audio
frequency waves are combined with waves at a much higher frequency, called
radio frequency, produced by an oscillator. These are known as carrier waves
because they carry the program signal. The radio frequency waves are modulated
either by amplitude modulation, in which their amplitude varies to match
changes in the program signal, or by frequency modulation (FM) in which their
frequency varies. The modulated signal is amplified to increase its power. The
amplified modulated signal is passed to an antenna from which it is transmitted
each station broadcasts on a different channel (its assigned frequency measured
in units called hertz.
The
receiver aerial picks up the radio waves carrying the signal, the signal, which
has become very weak following its transmission, is amplified, the rectifier
removes half the voltage swing in the
amplified signal, the signal is separated from the carrier waves, the signal is
again amplified in order to drive the loudspeaker, the loudspeaker converts the
electrical signal back into sound waves which can be heard.
