Assignment No. 1 for Communication Engineering, 4th sem IT students (to be submitted in class on 26/02/2013) Q. 1 A carrier signal with a peak voltage of 50V is amplitude modulated with a 1KHz test tone. The modulation voltage has an effective value of 5V. Compute the following: a. The percent modulation m b. The instantaneous voltage of positive and negative envelope when the 1KHz sine wave has completed 810 ������s of its cycle. c. Illustrate the waveform showing voltage levels and times. Q.2 Repeat Q.1 for a 2KHz test tone. Q.3 An AM signal with a peak carrier voltage of 12V has been amplitude modulated with a 5KHz sine wave. The stations broadcast frequency is 1MHz. Compute the following: a. The upper and lower sideband frequencies b. The peak carrier voltage Vc c. The percent modulation m d. The modulation voltage Vm e. The upper and lower sideband voltages Q.4 A spectrum analyzer is used to verify an FM signal with a carrier frequency of 106.5 MHz, a modulation frequency of 7.5KHz and a modulation index of 3.0. a. Determine the number of significant sideband pairs (Hint: Look up the Bessel table in your text book) b. Draw the output (spectrum) of the spectrum analyzer, showing relative amplitudes of each sideband pair. c. Compute the frequency deviation ������. Q.5 A PM signal is given by s(t)=Acos(wct+ PMm(t)+������), where m(t) has maximum frequency wm. a. Show that this signal can be approximated by the following: ������_������������������������������������(t)=C cos(wct+������)+ Dm(t)sin(wct+������) b. Determine the parameters C and D in the above equation.
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