Question

stion 2) [20 marks] Switching modulator is used to generate a modulated signal s(t) Assume m(t) = 4πcos(Zhoot) and c(t) = 32cos(2m10,000t) i. [1 marks] What type of modulation can the above modulator generate? ii. [3 marks] Draw a block diagram of the switching modulator. iii. [1 marks] Find the bandwidth of m(t) iv. [3 marks] Sketch the spectrum of s(t), then find its bandwidth. v. [2 marks] Is the transmission over modulated? Explain. vi. 12 marks] Modi fy the above modulator to generate lower side band modulated signal. b) [8 marks] Given g(t) = Σ®-00 2recte2 ). Sketch the spectrum of g(t) from-1.5 to 1.5 ㎐Then calculate the bandwidth that can give almost 95% of the total power

Answer 1

i) The switching modulation is used to generate the amplitude modulation signal (AM) (ii) switching modulator (iii) m(t) = 4 pi cos(2 pi 1000t) = Am cos (2 pi fm t) fm = 1000 HZ Band width (BW) of m(t) is fm = 1000HZ \r\n/(iv) V_2(t) = av_1(t) + b v^2_1(t) = a(c(t) + m(t)) + b (c(t) + m(t)) ^2 = a(c(t) + m(t)) + b (c(t) + m(t)) ^2 = a(c(t) + m(t)) + b(c^2(t) + m^2(t) + 2c(t) m(t)) in v_2(T) WE HAVE Am modulated signal that is = ac(t) + 2b c(t) m(t) s(t) = ac(t) [1 + 2B/A M(T) } = 32A COS(2 PI, 1000T) {1 + 2b/a 4 pi cos (2 pi 1000 t) } Band width (BW) = 2 fm = 2 times 1000 = 2000 HZ \r\n/v) Transmission over modulation Modulation is nothing but conversion of low frequency modulating signal to high frequency carier signal As frequency of signal increase transmitting antenna size is decreases