Q. Let m₁(t) and m₂(t) be two message signals, and let u₁(t) and u₂(t) be the corresponding modulated versions.

(a) When the combined message signal m₁(t) + m₂(t) DSB modulates a carrier Ac cos 2πf_ct , show that the result is the sum of the two DSB AM signals u₁(t) + u2(t). That is to say, AM satis?es the superposition principle.

(b) If_m1(t)+m₂(t) frequency modulates a carrier, show that the modulated signal is not equal to u₁(t) + u₂(t). That is to say, FM does not satisfy the principle of superposition, and angle modulation is not a linear modulation method.