Question

(SULIT) d. A coherent detector is used to demodulate Amplitude Modulated Single Side Band Suppressed Carrier (AMSSBSc) as shown in Figure Q1(d). Explain mathematically the effect on the output signal vo(t) when there is a phase difference between the AMssesc and the local oscillator vc(t). (CO1: P01 - 5 marks) X(t) AMssesct) х LPF Multiplier Figure Q1(d)

Answer 1

General SSB is Az MH) (05217fct Milt) semerfct 2 Ас 4 mt) SSB LPF SHEL Aclosenfct LO The output of the multiplier is (sse) (LO) le Am Em(t) tos ²21 fct Ac 6 t). Sim20ft ex20ft + 2 v 2 2 + AC mt) + 4 A² q m/t) 03(477ct) A c m (t). Sinatfet 4 ( high-frequency 2 Components Ac mit) Cole olp of LPF ) 4 Assume that the phase shift is present in the local- oscillator Olp. Then the olp of LPF is प A mt)(050 I Ac mits sind Ang pake som 0=0 At m(t) и ¢=90° A(² m(t) 4 NO Quadrature NULL effect

m/t) ma mm mit) 0<$<90) When the phase shift is ble o to 90² Coc the Demodulator Olp consists of mt) and ñt), In this case Demodulation is not possible & Synchronisath is required blw the TX & RX.