Physics, asked by nitinsher1936, 1 year ago

Why pam is not preferable in digital transmission?

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Answered by ashwani381
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 Best Answer

Pulse Amplitude Modulation suffers from the fact that information is encoded by varying the amplitude of pulses sent through some medium (e.g. over a cable, via RF, optically, etc.) PAM is essentially AM, but quantized in both time and amplitude. 

The most prominent disadvantage of PAM is that most transmission mediums exhibit some 'loss', and so the received pulse stream will be distorted in terms of amplitude -- which means, in turn, that the received information may be distorted as well! Other forms of digital modulation such as PWM, PPM and PCM are much less sensitive to amplitude distortions by the transmission medium, and so are much better suited for digital transmission. 

A secondary disadvantage of PAM is that it cannot be processed directly by digital circuitry and so PAM receivers are more complex in terms of implementation. Because PAM is essentially multi-level logic, before it may be processed by a binary ("digital") system is must be converted into a stream of binary words via an Analog-to-Digital converter. PPM, PWM, and PCM on the other hand can be oversampled and "sliced" into a stream of single bits and processed directly by digital circuitry.

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