- Question 1 1 1 A Test Engineer Uses A Modulating Signal G T 5 Sin 271000t N V To Create A Full Am Modulated Sig 1 (397.41 KiB) Viewed 25 times
thank you in advance for answering this questionQuestion: 1 1.1 A test engineer uses a modulating signal g(t) = 5 sin(271000t + n) [V] to create a Full-AM modulated signal s(t). The carrier used is c(t) = 10 sin(27106t) [V], and the amplitude sensitivity ka = 0.1. (a) Write a mathematical expression for the Full-AM modulated signal s(t). (b) Compute the value of the modulation index m. (c) Sketch at least 2 ms of f(t) in the time domain. (d) Sketch the single-sided PSD for g(t), c(t) and s(t). (e) What effect does the ‘+r' in the definition of g(t) have on the spectrum of $(t)?, explain your reasoning. Show your work and ensure that your sketches are neat and legible with all axes labelled / annotated appropri- ately. [40%] 1.2 For any modulation scheme we could define power efficiency, np, and bandwidth efficiency, Now, as: np = the ratio of the power in the information bearing components of the modulated signal to its total power. • Now = the ratio of the bandwidth of the modulating signal to the bandwidth of the modulated signal. (Ideally we'd like these both to be 100%). Using maths and/or sketches, compare np and now for the following schemes: Full-AM, DSB-SC, SSB-SC and QAM. Comment on your findings. [30%] 1.3 A DSB-SC signal, š(t), can be created using the circuit in Fig. 1. g(t) s(t) c(t) = Accos(21 fet) Figure 1: A possible DSB-SC modulator. The local oscillator used to generate c(t) can be challenging to design and implement, whereas a square wave generator having the same frequency is easily generated in a digital integrated circuit. Explain how one could use a square wave instead of c(t) to generate the DSB-SC signal and clearly outline what additional circuit elements would be required to achieve this. Illustrate your answer with diagrams and maths as appropriate. (30%)