Envelope Detector - Definition of The Envelope

Definition of The Envelope

Any AM or FM signal can be written in the following form

In the case of AM, φ(t) (the phase component of the signal) is constant and can be ignored. In AM, the carrier frequency is also constant. Thus, all the information in the AM signal is in R(t). R(t) is called the envelope of the signal. Hence an AM signal is given by the equation

with m(t) representing the original audio frequency message, C the carrier amplitude and R(t) equal to C + m(t). So, if the envelope of the AM signal can be extracted, the original message can be recovered.

In the case of FM, the transmitted signal has a constant envelope R(t) = R and can be ignored. However, many FM receivers measure the envelope anyway for received signal strength indication.

Read more about this topic:  Envelope Detector

Famous quotes containing the words definition of, definition and/or envelope:

    Beauty, like all other qualities presented to human experience, is relative; and the definition of it becomes unmeaning and useless in proportion to its abstractness. To define beauty not in the most abstract, but in the most concrete terms possible, not to find a universal formula for it, but the formula which expresses most adequately this or that special manifestation of it, is the aim of the true student of aesthetics.
    Walter Pater (1839–1894)

    Was man made stupid to see his own stupidity?
    Is God by definition indifferent, beyond us all?
    Is the eternal truth man’s fighting soul
    Wherein the Beast ravens in its own avidity?
    Richard Eberhart (b. 1904)

    Geroge Peatty: I’m gonna have it, Sherry. Hundreds of thousands, maybe a half million.
    Sherry Peatty: Of course you are, darling. Did you put the right address on the envelope when you sent it to the North Pole?
    Stanley Kubrick (b. 1928)