A radio frequency wave may be modulated in accordance with intelligence to be transmitted by varying either the amplitude or the frequency of the r.f. oscillations. In an amplitude modulated wave, the amplitude of the r.f. oscillation is varied in accordance with the intelligence to be transmitted, while the frequency of the oscillations is maintained constant. The intelligence to be transmitted usually consists either of an audio modulating signal with the frequencies in the range 20 Hz to 20 kHz or a video modulating signal, with frequencies from dc to several megahertz. The modulating signal is superimposed upon the radio frequency carrier by applying both to a nonlinear impedance (e.g. the modulator). When this is done, the modulating ...

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