Figure 1: Multiplexing System.
1. (20 points) Problem 1:
1. An Amplitude modulated (AM) signal is given by AM(t) = [A+m(t)]cos!ct, let m(t) = µAcos!mt. Forµ= 0.75, find the power efficiency.
2. For the multiplexing shown in the figure:
(a) (5 points) Sol
(b) (5 points) What must be the bandwidth of the channel ? (i.e what is the total bandwidth at point c?) Compare with the bandwidth required if the two signals were transmitted using QAM.
(c) (5 points) Design an efficient receiver signals m1(t) and m2(t) from the modulated signal at pointc. Note: No bandpss filter can be used. You can add boxes as required.
1. Two carriers of the same frequency but with di↵erent phases. XIt is the Correct Answer
2. Two carriers of the same frequency and phase.
3. One carrier.
4. Two carriers of the same phase but with di↵erent frequencies.
(b) (2 points) QAM signal can be:
1. m1(t)sin!ct+m2(t)cos!ct XIt is the Correct Answer 2. m1(t)cos!ct+m2(t)sin!ct XIt is the Correct Answer 3. m1(t)cos!ct+m2(t)cos!ct
4. m1(t)sin!ct+m2(t)sin!ct
(c) (2 points) If B is the bandwidth of the message signal m(t), the bandwidth of the SSB modulated signal is:
1. B XIt is the Correct Answer 2. 2B
3. 4B 4. None
(d) (2 points) Using Selective Method to generate an USB signal, the filter used has the following characterstics:
1. LPF with band 0 toB
2. BPF with band!c to!c+B XIt is the Correct Answer 3. BPF with band!c bto!c
4. BPF with band!c btoB
(e) (2 points) The block diagram shown above represnts:
1. Selective-Filtering SSB modulator with Multipliers in missing blocks.
2. Phase-Shift SSB modulator with Phase shifters of ⇡/2 XIt is the Correct Answer 3. Coherent SSB demodulator with Phase shifters of⇡/2
4. QAM modulator with Hilbert transformers.
(f) (2 points) Rectifier detection and envelop detection techniques are:
1. Synchronous 2. Coherent
3. Non-coherent XIt is the Correct Answer 4. 1. and 2.
(g) (2 points) A message signal m(t) lies between 5 and 1mV. What is the minimum value of the o↵set Ato generate an AM signal that can be correctly recovered by an envelope detector?
1. 1 mV XIt is the Correct Answer 2. 2 mV
3. 3 mV 4. 4 mV
(h) (2 points) For the signal m(t) described in previous question, what is the value of A required to achieve 85% modulation index?
1. 0 mV
2. 1.529 mV XIt is the Correct Answer 3. 2.529 mV
4. 3.529 mV
(i) (2 points) The outputvc(t) of the following circuit is:
1. A+m(t)
2. |A+m(t)| XIt is the Correct Answer 3. m(t)
4. |m(t)|
3. (20 points) Problem 3. Fill and sketch;
• For a tone modulation with 2 KHz message frequency, and 10 KHz carrier frequency. Fill the following:
• For a Rectifier Detector shown above, fill the gaps:
Given that Fourier seriers of a square wave which lies between 0 and 1and has the period 2⇡/!c
is:⇥1
2+ 2⇡ cos!ct 13cos3!ct+15cos5!ct ... ⇤
