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linear vs. nonlinear modulation

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saeddawoud

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Hello every body
What is the formal definitions of linear and nonlinear modulations. And why PSK is a linear while FSK is a nonlinear modulation technique?
 

Linear modulations are characterized by a bandwidth amplitude B which is equal to the modulation signal. AM is a linear modulation the modulated and the modulating signal present the same bandwidth amplitude centered respectvely on the carrier frequency and the zero frequency. Furthermore the modulation does not affect the spectral content of the modulating signal: the ratio between two harmonic components of the modulating signal is leaved unchanged by the modulation.

Non linear modulation act as nonlinear system: the bandwidth of the modulated signal is wider and can be alterated in terms of ratio between two spectral components with respect to the modulating signal.

I hope is clear.

Bye
 

>> And why PSK is a linear while FSK is a nonlinear modulation technique?


I am not so sure if PSK is linear. Your comments ppl.
 

if u have modulator produce y1(t) for input x1(t)
and produce y2(t) for input x2(t)
we say the system is linear if we make the input = x(t) = ax1(t)+bx2(t)
and the output becom y(t)= ay1(t)+by2(t)

I dont thing thant any of PSK or FSK is a linear modulator
 

PSK is a linear modulation technique as it is generated by a linear methods, eg. the phase of the carrier is changed linearly with the input modulating signal, same is true for the ASK where amplitude is varied linearly according to the input information bearing signal. The same applies to QAM modulation techniques which are combination of both PSK and ASK. On the otherhand FSK type modulation techniques are non-linear due to the fact these are generated non-linearly by having the phase of the carrier generated by integrating the input signal (to be modulated).
 

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