Envelope Modulation

  • R. F. W. Coates
Part of the Electrical and Electronic Engineering book series


We have defined the general modulated sinusoid, in section 2.14, as
$$ v\left( t \right) = A\left( t \right)\cos \left\{ {2\pi {f_c}t + \phi \left( t \right)} \right\} $$
The amplitude and phase terms are some functions of the modulating signal vm(t), as yet undefined, so that
$$ \begin{array}{*{20}{c}} {A\left( t \right) = {g_1}\left\{ {{v_m}\left( t \right)} \right\}} \\ {\phi \left( t \right) = {g_2}\left\{ {{v_m}\left( t \right)} \right\}} \end{array} $$
There are three principle reasons for modulating a sinusoidal carrier
  1. (1)

    To relocate baseband information so that it is spectrally adjacent to the high-frequency carrier. This frequency translation makes electromagnetic propagation much easier. Both transmission power and antenna size may be reduced as the carrier frequency is increased.

  2. (2)

    To provide the capability of frequency division multiplexing many baseband channels.

  3. (3)

    To increase the transmitted signal (that is, the modulated carrier) redundancy, thereby gaining a measure of immunity to the signal corruption introduced by the channel.



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Copyright information

© R. F. W. Coates 1982

Authors and Affiliations

  • R. F. W. Coates
    • 1
  1. 1.University of WalesUK

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