Tut of Electronics Essay

Published: 2020-02-03 00:22:36
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Tutorial Sheet # 2 1. Sketch the time variation and frequency spectrum of an RF signal with 75 % Amplitude Modulation. Show several cycles of the modulated wave. Make the modulation frequency 1/10 of the carrier frequency. The unmodulated carrier has peak amplitude of 1.0V. In an amplitude modulation system, the message signal is given by Fig. and the carrier frequency is 1 KHz. The modulator output is SAM (t) = 2(b + 0.5m (t)) cos ωc t.


a. Determine the average message power. b. If b = 1, determine the modulation index and the modulation power efficiency. c. Sketch the modulated signal of part (a) in the time domain. d. If b = 0.5, repeat part (b). 3. The output signal from a DSB-SC AM modulator is u(t) = 20 cos(300πt) + 6 cos(280πt) + 6 cos(320πt) a. Determine the Fourier transform U (f) of u (t). b. Determine the normalized message signal mn(t) (which satisfies max{lmn(t)l} = 1) and the carrier signal c (t). c. Determine the average power of u (t). d. Determine the modulation index. e. Determine the modulation efficiency. You are asked to design a DSB-SC modulator to generate a modulated signal km (t) cos ωc t where m(t) is a signal bandlimited to B Hz. Figure shows a DSB-SC modulator available in the stockroom. The carrier generator available generates cos3 ωc t instead of cos ωc t. Explain whether you would be able to generate the design using only this equipment. You may use any kind of filter you like.



The system shown in Fig. is used for scrambling audio signals. The output y (t) is the scrambled version of the input m (t).


Two signals m1 (t) and m2 (t) with amplitude spectra M1 (f) and M2 (f) given below are to be transmitted simultaneously over a channel by the multiplexing scheme shown in the block diagram below. The signal b (t) is the multiplexed signal, which is modulated by a carrier, resulting in the signal c (t) transmitted over a channel.

a. Sketch the amplitude spectra of the signals a(t), b(t) and c(t) in the block diagram, respectively. Label the amplitude and the frequency axes. b. Determine the bandwidths of the signals a(t), b(t) and c(t), respectively. c. Design and sketch the block diagram of a receiver that will recover signals m1(t) and m2(t) from the modulated signal c (t). Specify the type and the cutoff frequency for every filter you use in your design, give the specifications for any other component you might use.

7. A message signal m (t) = cos (2000πt) + 2cos (4000πt) modulates the carrier c (t) = 100cos (2πfc t), where fc =1MHz to produce the DSB signal m (t).c (t). a. Determine the expression for the upper-sideband (USB) signal. b. Determine and sketch the spectrum of the USB signal. A message signal m(t) = cos(2πfmt) is used to amplitude modulate a carrier with frequency fc. The modulated signal is given by u(t) = Aβ cos[2π(fc fm)t] + A(1 β) cos[2π(fc + fm)t] ; where 0 ≤β≤1. a. When β = 0, determine the type of the resulting AM modulation. b. When β = 1, determine the type of the resulting AM modulation. c. When β = 0.5, determine the type of the resulting AM modulation. d. When β = 0.1, determine the type of the resulting AM modulation.


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