Pokhara University
Level: Bachelor / Semester – Fall / Year : 2005Programme: BE. / Full Marks: 100
Course: Analog Communication / Time : 3hrs.
Candidates are required to give their answers in their own words as far as practicable.
The figures in the margin indicate full marks.
Attempt all the questions.
1. / a) Draw the functional block diagram of a communication system and explain each block briefly.b) Explain the importance of channel bandwidth with the help of Hartley-Shannon law.
c) What is modulation? Discuss about the necessity of modulation in communication. / 7
4
4
2. / a) Define Hilbert transform. Determine the Hilbert transform of
x(t) = A cos (2pf0t + q).
b) Calculate the percentage of power saved when the carrier is suppressed in an AM wave modulated to a depth of
i) 80% and ii) 60%
c) Define band pass systems and band-limited signals. / 2+4
3+3
3
3. / a) Suppose that the modulation signal m(t) is a sinusoid of the form
m(t) = a cos 2pfm t fm < fc
Determine the DSB – SC AM signal and its upper and lower sidebands.
b) Explain the various methods used in the generation of a SSB – SC wave.
c) Explain the principle of an envelope detector with a circuit diagram. / 4
7
4
4. / a) Describe in detail, how PLL can be used in carrier synchronization in AM systems.
b) Explain the coherent detection method of demodulation of SSB – SC wave. Can we use this method to demodulate DSB – SC AM signals? Explain. / 7
8
5. / a) Derive the Fourier series representation of single – tone FM wave.
b) The carrier c(t) = Acos2p106 t in angle modulated (PM or FM) by the sinusoidal signal m(t) = 2cos2000pt. The deviation constants are kp = 1.5 rad/v and kf = 300 Hz/V.
Determine
i) modulation indices of PM and FM systems.
ii) the bandwidth in each case using Carson’s rule. / 7
4+4
6. / a) What is broadcasting? What are its types? Explain each of them briefly.
b) How CCITT standard Groups, Supergroups and Mastergroups are formed using SSB – SC in telephone? Explain. / 2+2+4
7
7. / Write short notes on (Any Two)
a) Balanced modulators
b) Distortion less transmission line
c) Multiplexing
d) Generation of FM using Armstrong’s method. / 2´5
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Pokhara University
Level: Bachelor / Semester – Fall / Year : 2007Programme: BE / Full Marks : 100
Course: Analog Communication / Time : 3hrs.
Candidates are required to give their answers in their own words as far as practicable.
The figures in the margin indicate full marks.
Attempt all the questions.
1. / a) Explain in brief the different blocks of a typical communication system with neat diagram. List out the need of modulation.b) State and explain channel capacity theorem. Calculate the maximum data rate that could be sent over a telephone lines, whose S/N ratio is 39 dB and passes over the frequency range from 300-3400 Hz. / 7
8
2. / a) A DSB-AM signal is modulated be m(t) = cost + 2cos2t, where = 2π f1 , f1 = 500Hz. The carrier signal is
i) Write an expression for the DSB-SC signal and sketch a picture of its spectrum.
ii) Find the value of the average power.
b) Explain phase-shift method of generating SSB signal. / 8
7
3. / a) An AM broadcast radio transmitter radiates 1200 watts of power at 70 percent modulation. Calculate the carrier power and power content of each of the side bands.
b) Explain Superhetrodyne Receiver for standard AM Radio with block diagram and working principle. / 7
8
4. / a) Explain the demodulation of DSB-SC signal by a Costas loop. Also explain how it overcomes the problem imposed by the phase error in a simple product modulator coherent receiver.
b) If c(t) = 20 cos 50000 (t), m(t) = 20cos(50000t + 6 sin 1000t), describe
i) Modulation index
ii) Peak Frequency deviation
iii) Bandwidth of modulated signal
iv) Modulated signal power dissipated in 15Ω resistance / 7
8
5. / a) List out the advantages and disadvantages of Frequency Modulation over Amplitude Modulation.
b) For the following Armstrong FM transmitter compute maximum frequency deviation and the carrier frequency fc if, f1 = 200 kHz, fLO = 10.8 MHz, ∆f1 = 25Hz, n1 = 64 and n2 = 48. / 7
8
6. / a) Describe FDM and FDMA. Explain different FDM hierarchy.
b) Explain feasibility and importance of satellite communication in the context of a topographically diverse and economically poor country like Nepal. / 8
7
7. / Write short notes on (Any Two)
a) Ideal low pass filter
b) Phase Locked Loop (PLL)
c) Filters and oscillators requirements in FDM / 5×2
Pokhara University
Level: Bachelor / Semester – Fall / Year : 2009Programme: B.E. / Full Marks : 100
Course: Analog Communication / Time : 3hrs.
Candidates are required to give their answers in their own words as far as practicable.
The figures in the margin indicate full marks.
Attempt all the questions.
1. / a) Give the block diagram of a communication system. And explain each of them in brief.b) In an AM signals contains 700W at its carrier frequency and 300 W in each of its sidebands.
i. Determine the percent of modulation of the AM signal.
ii. Find the allocation of power if the percent of modulation is changed to 80% / 8
7
2. / a) Write basic equations for FM and PM with neat diagram.
b) Why SSB is more important in communication application. Draw the block diagram of a phase cancellation SSB generator and explain how the carrier and unwanted sidebands are suppressed. / 8
7
3. / a) Show that the transmission bandwidth required for the transmission of the AM modulated wave is twice the frequency of the message signal used.
b) Derive the expression for the SSB modulated wave. / 7
8
4. / a) Discuss the effect of frequency and phase errors in the local oscillator in the DSB-SC modulated wave.
b) Make the use of PLL to demodulate the FM modulated wave. / 8
7
5 / a) How can you generate a FM modulated wave using a phase modulator? And how can you generate a PM modulated wave using a frequency modulator. Explain with the help of a neat diagram.
b) Define Carson's rule. If / 8
7
6. / a) List out the advantages and application of satellite system.
b) Discuss different modulation techniques used in radio communication system. / 7
8
7. / Write short notes on (Any Two)
a) Hilbert transform and its properties
b) Satellite systems and application
c) Multiplexing / 5x2
Pokhara University
Level: Bachelor / Semester – Spring / Year : 2009Programme: BE / Full Marks: 100
Pass Marks: 45
Course: Analog Communication / Time : 3hrs.
Candidates are required to give their answers in their own words as far as practicable.
The figures in the margin indicate full marks.
Attempt all the questions.
8. / a) Explain in brief the different blocks of typical communication system with neat diagram. List out the need of modulation.b) Explain the importance of channel bandwidth with the help of Hartley-Shannon law. Calculate the maximum data rate that could be sent over telephone lines, whose S/N ratio is 25 db and passes over the frequency range from 300 -3200hz. / 7
8
9. / a) For an AM DSB-SC transmitter with an unmodulated carrier power Pc = 100W that is modulated simultaneously by three modulating signals with coefficients of modulation m1=0.2, m2=0.4, m3=0.5, determine;
i. Total coefficient of modulation
ii. Upper & Lower sideband power
iii. Total transmitted power
b) Draw DSB-AM signal spectrum and hence find out its bandwidth requirement.
c) Compare DSB-AM, DSB-SC and SSB-SC with respect to transmission power, transmission bandwidth and receiver complexity. / 6
3
6
10. / a) How do you synchronously demodulate an AM modulated wave?
b) The maximun and minimum amplitude of an A M modulated wave are Amax=10mV & Amin=0mV respectively.Calculate the modulation index, µ.
c) Name the three components used in a PLL. Give the two applications for a PLL. / 5
5
5
11. / a) What is a narrowband FM (NBFM) wave? Derive the time domain expression for the narrowband FM modulated wave.
b) What is the effect of the variation of the modulating signal frequency in the spectrum of the WBFM if the amplitude of the modulating signal is kept constant and the modulation index is increased gradually? Explain with the help of a neat diagram. / 7
8
12. / a) Explain phase-shift method of generating SSB signal.
b) The maximum deviation allowed in an FM broadcast is 75 KHZ .If the modulating signal is a single-tone sinusoid of 10 KHZ. Find the bandwidth of the FM signal .What will be the change in the bandwidth. If modulating frequency is doubled? Determine the bandwidth when modulating signals amplitude is also doubled. / 7
8
13. / a) Explain feasibility and the importance of Satellite Communication in long distance call.
b) Show, diagrammatically and with an explanation how channel are combined into groups and groups into super groups and so on, when FDM is generated in practical system. / 7
8
14. / Write short notes on (Any Two) :
a) Multiple access techniques.
b) Modes of propagation of electromagnetic waves.
c) Broadcast techniques. / 5×2
Pokhara University
Level: Bachelor / Semester – Fall / Year : 2010Programme: BE / Full Marks : 100
Pass Marks: 45
Course: Analog Communication / Time : 3hrs.
Candidates are required to give their answers in their own words as far as practicable.
The figures in the margin indicate full marks.
Attempt all the questions.
1. / a) Draw a block diagram of a communication system and explain the function of each block.b) An AM signals contains 550W at its carrier frequency and 150 W in each of its side-bands.
i. determine the percent of modulation of the AM signal.
ii. find the allocation of power if the percent of modulation is changed to 90%
c) Define Hilbert transform and state its properties. / 5
5
5
2. / a) Explain amplitude modulation with its time domain expression. What is the impact of carrier transmission in power and bandwidth requirement?
b) Explain the balanced modulator method of DSB generation with necessary expression. / 7
8
3. / a) Explain super-heterodyne receiver for standard AM radio with block diagram and working principle.
b) With the help of necessary diagrams and waveforms of envelop detector, explain how it detects DSB-AM signals? / 8
7
4. / a) Briefly explain the generation of FM using Armstorng's method.
b) What are the differences between NBFM and WBFM. Show how WBFM signal is generated using NBFM signal. / 7
8
5. / a) An Armstrong FM modulator is required in order to transmit an audio signal of bandwidth 50 Hz to 15 KHz. The narrowband phase modulator used for this purpose utilized a crystal controlled oscillator to provide a carrier frequency MHz. The output of the narrowband phase modulator is multiplied by by a multiplier and passed to a mixer with a local oscillator frequency = 10.925 MHz, and a frequency deviation ∆f =75 KHz, which is obtained by multiplying the mixer output frequency with using another multiplier. Find and . Assume that NBFM produces deviation of 25 Hz for the lowest baseband signal.
b) What are FDM and FDMA? Derive analog telephone hierarchy from CCITT standard group, super group and master group with sketch of frequency spectrum. / 8
7
6. / a) With a block diagram explain a communication satellite system. Also state the scope of communication satellite in topographically diverse and economically poor country like Nepal.
b) What is broadcasting? What are its types? Explain each of them briefly. / 7
8
7. / Write short notes on: (Any Two)
a) PLL
b) Ideal LPF and distortionless transmission
c) FDM and FDMA / 5x2
Pokhara University
Level: Bachelor / Semester – Spring / Year : 2010Programme: BE / Full Marks: 100
Course: Analog Communication / Pass Marks: 45
Time : 3hrs.
Candidates are required to give their answers in their own words as far as practicable.
The figures in the margin indicate full marks.
Attempt all the questions.
15. / a) Name the three sub-systems involved in the block diagram of a communication system.b) State and explain the channel capacity theorem. Calculate the maximum data rate that could be send over a telephone line whose S/N ratio is 20dB and passes over the frequency range from 300-3400 Hz.
c) If m (t)=Amcos (2 πfmt). Find its Hilbert transform. / 5
5
5
16. / a) Define pre-envelope, complex envelope and natural envelope of a bandpass signal.
b) Explain the operation of ring modulator for the generation of DSB-SC signal.
c) Calculate the percentage of power saved when the carrier and one of the sidebands are suppressed in an AM wave modulated to a depth of 50% and 100%. / 3
7
5
17. / a) Derive the power relationship between the total sideband power and the total power in the AM wave. Assume m (t) = Amcos (2πfmt ) and c (t)= Accos (2πfct) for you calculations.
b) Briefly discuss the filter method for generation of SSB signal. Compare DSB-SC and SSB-SC with respect to transmission power, transmission bandwidth and receiver complexity. / 8
7
18. / a) Explain how envelope detector works along with necessary conditions for charging and discharging time constants.
b) What is the reason behind using the SSB-SC modulated wave in telephony?
c) A single tone FM is represented by the voltage equation as:
V(t) =12 cos (6×108t+5sin 1250t)
Determine the carrier frequency, modulating frequency, modulation index, maximum deviation. What power will this FM wave dissipate in 10Ω resistor? / 4
3
8
19. / a) What is a wideband FM (WBFM) wave? Derive its frequency domain expression. Also, show that there exist an infinite number of the side frequencies in its spectrum.
b) Explain the working principle of the FM stereo transmitter with the help of a neat diagram. / 10
5
20. / a) What are the types of modulation used in television broadcasting system?
b) Why the filters and oscillators are important in FDM system.
c) What are the three different modes of propagation of radio frequencies? / 8
5
2
21. / Write short notes on any two:
a) DTH companies in Nepal
b) Distortionless Transmission
c) Multiple access techniques / 2×5
Pokhara University