While the exact shape of the response is not crucial, it must have odd symmetry above the carrier frequency and a relative response of 1/2 at fc . The filter response is designed so that the original message spectrum M (ω) is reproduced on demodulation as a result of the superposition of two spectra: On demodulation, - The positive frequency part of S(ω) {i.e. spectrum of transmitted signal s(t)} is shifted downward in frequency by fc. - The negative frequency part of S(ω) is shifted upward in frequency by fc .
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