2)(20 marks] AS(t) . Amoy 2 1 max A single-tone message signal, m(), at 500 Hz w

Question

2)(20 marks] AS(t) . Amoy 2 1 max A single-tone message signal, m(), at 500 Hz with a power of 8 watt is used to amplitude modulate a KHz carrier with ka 0.1. If the resulting amplitude modulation (AM) wave is shown above: a) [2] Find the modulation factor, . b) [2] Find the amplitude of the carrier, Ac c) [2] find Amin of the AM wave. d) [2] Write a time-domain expression for the AM wave. e) [3] Sketch the spectrum of the AM wave. f) [1] Find the bandwidth of the AM wave. g) [3] Find the carrier power, LSB power, USB power, total power, and power efficiency. h) [5] Draw the envelop detector circuit, then specify the two design requirements for the charging discharging time constants

Explanation / Answer

Answer:-a) Power of single tone signal = A2/2 = 8, so A = 4 is the amplitude of message signal.
Modulation factor(meu) = ka x A = 0.1x4 = 0.4.

b) Amax = (1 + 0.4)AC   => AC = 15.

c) Amin = (1 - 0.4)AC = 9.

d) Time domain expression is s(t) = AC[1 + (meu)m(t)].cos(2*pi*fC*t) = 15[1 + 0.4sin(2*pi*500*t)].cos(2*pi*fC*t). Keep value of fC as it is not shown in figure.

g) Band-width of AM is BW = 2*fm = 2*500 Hz = 1 kHz.

For other parts of question, carrier frequency is required.

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