Figure shows the block diagram of Weaver?s method for generating SSB modulated waves. The message (modulating) signal m (t) is limited to the band ?_a | ? | ?_b. The auxiliary carrier applied to the first pair of product modulators has a frequency ?₀, which lies at the center of this band, as shown by ?₀ = ?_a + ?_b/2. The low-pass filters in the in-phase and quadrature channels are identical, each with a cutoff frequency equal to (?_b ? ?_a)/2. The carrier applied to the second pair of product modulators has a frequency ?_c that is grater than (?_b ? ?_a)/2. Sketch the spectra at the carious points in the modulators of Figure, and hence show that:

(a) For the lower sideband, the contribution of the in-phase and quadrature channels are of the same polarity, and by adding them at the modular output, the lower sideband is suppressed.

(b) For the upper sideband, the contribution of the in-phase and quadrature channels are of the same polarity, and by adding them at the modular output, the upper sideband is suppressed

(c) How would you modify the modulator of Figure so that only the lower sideband is transmitted?

Transcribed Image Text:

In-phase channel Product Product Low-pass filter SSB m() Σ modulator modulator wave cos (2 f) cos (2=fo) Product modulator Low-pass fiter Product modulator sin (2mfo) sin (2mf.) Quadrature channel