Telcommunication laboratory ybu engineering solution homework quizz exam (14)

YILDIRIM BEYAZIT UNIVERSITY EE 305 – TELECOMMUNICATIONS 1 PRELIMINARY MANUAL – 1 – Amplitude Modulation & Demodulation Preliminary work: 1) An AM modulated signal SAM(t) = 5.cos (1800.π.t) +20.cos (2000.π.t) + 5.cos (2200.π.t) a-) Determine the modulating signal m(t) and the carrier signal c(t). b-) Determine the modulation index.

2) AM Signal has the form SAM(t) = [ 20 + 10.cos (20000π .t)] . cos (2π.100000.t) a-) Determine the modulating signal m(t) and the carrier signal c(t). b-) Determine the modulation index. c-) Sketch the phasor form(spectrum) of SAM(t).

3) A wiring diagram of TETRA-BB hardware blocks to generate an AM signal is given in Figure 1.

Figure 1: Wiring of TETRA-BB hardware blocks to generate an AM signal

a-) Draw the time domain expression of the output signal of master signals module tuned to 2 kHz for tone signal. It provides an output signal with a peak to peak amplitude of 4V (for a time range of 0- 2 ms). b-) Draw the time domain expression of the output signal of a master signals module tuned to give a sine wave of 100 kHz for carrier signal and a peak to peak amplitude of 4V (for a time range of 0 – 0.08 ms). c-) Draw the time domain expression of the output signal of a Variable DC module tuned to a -4V (for a time range of 0 – 2 ms). Please do not forget to DC signal is generated at positive side of y axis when you use negative DC voltage value due to Variable DC module specification or vice versa. d-) Draw the approximate time domain expression graphics for each of the following steps, according to connections in Figure 1. Use the master(tone) signal, the carrier signal and DC voltage value respectively in question 3-a, question 3-b and question 3-c:   

Output of the Adder module (for a time range of 0 – 2 ms).

Output of the Multiplier module (for a time range of 0 – 2 ms).

Assume that modulation index value is equal to 1 ( ma = 1 ).

e-) Draw the phasor forms of the signals obtained at output of the multiplier module. Also draw their amplitude spectrums.

A wiring diagram of TETRA-BB hardware blocks to demodulate an AM signal using demodulator with same mixer is given in Figure 2.

Figure 2 : Wiring of TETRA-BB hardware blocks to demodulate an AM signal using demodulator with a same mixer.

f-) Draw the phasor forms of the signals obtained output of the second multiplier module.

Comment on how to recover your master(tone) signal at receiver. g-) Draw the approximate both phasor form and time domain graphics of the output of a RC LPF module when we connect output of second multiplier module (for a time range of 0 – 2 ms). Is the signal same with the message(tone) signal? Comment on this.