( Coherent demodulation of DSB-SC or AM ) For the signals, s ( t ), of Problems 2.42 and 2.43, consider s 1 ( t ) = s ( t ) cos(2 π f c t ). Determine S 1 ( f ) and sketch the resultant spectrum. Let s 1 ( t ) be input to an ideal lowpass filter, bandwidth W hertz. What is the output? Repeat (a) and (b) but let s 1 ( t ) = s ( t ) sin(2 π f c t ).