Two signals m1 (t) and m2(1), both band-limited to 5000 Hz, aretobetransmitted simultaneously over a channel by the multiplexing scheme shown in Fig. P4.2-8. The signal at point b is the multiplexed signal, which now modulates a carrier of frequency 20,000 Hz. The modulated signal at point c is transmitted over a channel. (a) Sketch signal spectra at points a, b, c. and (b) What must be the bandwidth of the channel? (c) Design a receiver to recover signals m1(t) and m2(t) from the modulated signal at point c. Figure P.4.2-8 M(f)| --5000 5000 /- 2 cos 40,000t -5000 01 5000 f- 2 cos 20,000r A slightly modified version of this scrambler was first used commercially on the 25-mile radio- telephone circuit connecting Los Angeles and Santa Catalina island.