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Phase & Frequency Modulation Difference

March 18th Fact-of-the-Day

It is impossible to change the phase of a sinewave without changing its frequency. It is impossible to change the frequency of a sinewave without changing its phase. That being true, are phase and frequency modulation equivalent? The answer can be either 'yes' or 'no' depending on the modulating signal. The answer is 'yes,' the processes are exactly equivalent, if a sinewave is modulated by a single frequency. However, the answer is 'no' if a modulating signal has multiple frequency components, because phase modulation results in greater frequency-deviation at high, compared to low, modulating frequencies in comparison to frequency modulation. Therefore, the difference is merely a difference in modulation frequency response, making it possible to effectively convert one form of modulation to the other by simply modifying the amplitude vs. frequency characteristic of a signal prior to modulation. ©2005 Martek International All rights reserved.


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