ABSTRACT
Radio waves are described as being electromagnetic in character. For example, the waves used for radio and television transmission are electromagnetic waves and they are created by producing a high frequency current in an aerial. In fact electromagnetic waves are far more all-embracing than just the example of radio and television waves. Light, including ultraviolet and infrared rays and X-rays are all electromagnetic (e.m.) waves. Radio waves, and indeed all the other kinds of e.m. waves, are really only of interest to us if they are useful. Then the modulating frequency has to be allowed for, and a reasonable practical figure for the sidebands is to add the highest audio frequency to the deviation frequency. The big advantage of frequency modulation (f.m.) over amplitude modulation (a.m.) is that it is a system which is much less prone to interference, whether man-made or natural, for the reason that the effects tend to be amplitude effects.
