6.58 In World War II, voice radio scramblers used modulation schemes to distort a signal so that enemy forces could not understand it unless it was demodulated properly. In one scheme, a signal x (t), bandlimited to 4 kHz, is modulated to generate an output signal (a) Plot the range of the spectrum of y(t). (b) Describe why the scrambled signal's spectrum is ''distorted.'' (c) Show that x(t) can be recovered from y(t) using