Analog and Digital Communication: Previous Year Questions

Sorted Chapter Wise

Compiled by Grok
August 17, 2025

1 Chapter 1: Introduction to Communication System

• Compare Analog and Digital Communication.

• Justify: Noise immunity of digital communication system is better than analog communication system.
• Explain the need of modulation.
• What are the advantages of digital communication over analog communication?
• Draw and explain the basic block diagram of communication system.

• Explain Modulation process with its requirement in communication system.

• Explain different types of signal distortions over a communication channel.
• Explain Noise immunity of digital signals.

• Explain the classification of signals.

• “If SNR= Can we achieve Channel Capacity C= Practically?” Justify according to shanon’s equation.
• Define: Modulation, SNR and Channel capacity.
• Define following: 1) Amplitude modulation 2) Frequency modulation 3) Phase modulation

• State any four benefits of Modulation.

• What is modulation? Why modulation required? Describe in detail.
• Define: Modulation index, SNR and Channel capacity.

2 Chapter 2: Amplitude Modulation and Demodulation

• Give Comparison between Am and FM.
• Explain Vestigial Side Band AM in brief.

• An AM signal is represented by e(t) = (10+ 4 cos 1000 t ) cos (2 106 t). Find: Modulation index, total
power, sideband power, efficiency and transmission Bandwidth required for this AM signal.
• A 10 kw carrier wave is amplitude modulated at 80%. Compute sideband power, total power and efficiency.
• Compare DSB-FC, DSB-SC, SSB, VSB

• With related to Amplitude modulation discuss following parameters: (i) Modulation index (ii) Modulation
depth (iii) Bandwidth requirement

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• What are the advantages of Single Side Band (SSB) modulation over Double Side Band (DSB) modulation?
Explain filter method to generate SSB signal.
• A broadcast AM transmitter radiates 50 KW of carrier power. What will be the radiated power at 85%
modulation?

• Explain how the envelope detector demodulates AM signals. Also indicate the difference between the
rectifier detector and the envelope detector.
• A modulating signal 10sin (2*500t) is used to amplitude modulates a carrier of 50sin (2*100000t). Find
i) modulation index, ii) sideband frequencies, iii) amplitude of both side bands, iv) Total Bandwidth, v)
Total power delivered to load of 600, vi) power in carrier signal, vii) power in one sideband.

• Explain amplitude modulation with its mathematical expression and frequency spectrum. Draw its wave-
forms for under, perfect and over modulation.
• Amplitude Modulated wave has maximum and minimum amplitudes are measured as 7.2 V and 1.8 V
respectively. Calculate its modulation index and transmission efficiency.

• List the methods used to generate SSB modulation signal. Discuss any one method in detail.
• Explain vestigial sideband (VSB).
• “VSB is clever compromise between SSB and DSB for Broadcast Television” Justify.
• Briefly Describe L-carrier hierarchical long haul analog telephone FDM system.

• Briefly Describe Signal-Squaring Method of carrier regeneration using PLL at the DSB-SC receiver.
• Show that any scheme that can be used to generate DSB-SC can also generate AM.
• Determine and percentage of the total power carried by the side bands of the AM wave for tone modulation
when µ=0.6 and µ=0.4

• Describe SSB generation using the phase shift method.

• Show that any scheme that can be used to demodulate DSB-SC can also demodulate AM.
• Explain DSB amplitude modulation with necessary figures.

• Explain PLL.
• Write a note on Envelope detector.
• Show difference between AM and FM system.
• Discuss under modulation (undershoot), perfect modulation and over modulation (overshoot) for various
value of modulation index.
• How AM waves are detected in Envelop Detector method.
• The antenna current of an AM transmitter is 8 amperes (8A) when only the carrier is sent, but it increases
to 8.93A when the carrier is modulated by a single sine wave. Find the percentage modulation and also
determine the antenna current when the percent of modulation changes to 0.8.

• State difference between Single sideband and Double sideband amplitude modulation.
• An audio signal given as 15 sin (2(1500t)) amplitude modulates a carrier given as 60 sin (2(100,000t)).
Determine the following 1. Sketch the Audio signal 2. Sketch the carrier signal. 3. Determine the
percentage of index 4. Draw the frequency spectrum of modulated signal with all frequency component

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3 Chapter 3: Angle Modulation and Demodulation
• Give Comparison between Am and FM.
• What is Carson’s rule in FM?
• A 107.6 MHz carrier is frequency modulated by a 7 KHz sine wave. The resultant FM signal has a
frequency deviation of 50 KHz. i) Find the carrier swing of the FM signal. ii) Determine the highest and
lowest frequencies attained by the modulated signal iii) What is the modulation index of the FM wave?

• Discuss drawbacks of direct method for FM generation.

• An FM wave is given by e(t) = 10sin (5 × 108 t + 4sin1250t). Determine: (i) The carrier frequency (ii)
Modulating frequency (iii) The modulation index (iv) The maximum deviation.
• Explain the working of pre-emphasis network in Frequency Modulation.

• Compare: Amplitude Modulation and Frequency Modulation.

• Explain how FM signal is generated using Indirect method of Armstrong.
• An FM wave is given by e(t) = 20 cos[6 × 108t + 7 sin1250t]. Determine (i) The carrier frequency (ii)
Modulating frequency (iii) The maximum deviation.

• Why pre-emphasis and de-emphasis are used in FM transmitter and receiver?

• Discuss the advantages and disadvantages of Frequency Modulation over Amplitude Modulation.
• Discuss about Carson’s rule.

• Explain the indirect method of generating FM signal with block diagram and relevant mathematical
expression.
• State the unique features of FM.
• How the FM waves are generated?

• Explain Preemphasis and Deemphasis in FM broadcasting.

• What is modulation index for FM?
• Write a note on demodulation of FM.
• Write a note on FM receiver.

• State the Carson’s rule and explain in brief.

• A modulating signal 10 cos(2 • 30 x 103 t); Angle modulated a carrier Vc cos(wc • t). Calculate Modulation
Index and bandwidth for the FM system. (Assume Kf = 15 kHz)
• Enlist various methods of FM generation. Explain any one of them.

• Explain pre-emphasis and de-emphasis in relation to FM.

• A 107.6 MHz carrier is frequency modulated by a 7 KHz sine wave. The resultant FM signal has a
frequency deviation of 50 KHz. i) Find the carrier swing of the FM signal. ii) Determine the highest and
lowest frequencies attained by the modulated signal iii) What is the modulation index of the FM wave?

• Explain Armstrong method of FM generation with neat diagram.

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4 Chapter 4: Sampling and Analog to Digital Conversion
• State and prove sampling theorem. Also explain types of sampling in details.
• State and explain Sampling theorem.
• What is aliasing effect?
• Describe the effect of slope overloading and hunting in delta modulation.
• A compact disc (CD) records audio signals digitally by PCM. Assume audio signal’s BW to be 15 KHz. If
signals are sampled at a rate 20% above Nyquist rate for practical reasons and the samples are quantized
into 65,536 levels, determine bps required to encode the signal and minimum BW required to transmit
encoded signal.
• Discuss advantages and disadvantages of delta modulation.
• What is companding process in PCM? State laws for the same.
• A TV signal having a BW of 4.2 MHz is transmitted using binary PCM system. Given that the number
of quantization levels is 512. Determine Code word length, Transmission BW, Final bit rate and Output
signal to quantization noise ratio.
• Explain the principle of non uniform quantization.
• What is aliasing? How aliasing can be eliminated?
• Find the Nyquist rate and Nyquist interval for the signal x(t) = 10 cos3000t cos1000t
• Explain the working of delta modulation with the help of block diagram. Discuss the disadvantages of
delta modulation.
• Explain the operation of sample and hold circuit.
• State and prove sampling theorem in time domain.
• Differentiate Delta modulation and Adaptive delta modulation. Discuss the condition for avoiding slope
overload error?
• Briefly describe the types of sampling and its importance.
• Explain Time Division Multiplexing for PCM in T1 carrier systems.
• A signal m(t) of Bandwidth B=4kHz is transmitted using a binary companded PCM with µ=100. Compare
the case of L=64 and L=256 from the point of view of transmission bandwith and the output SNR.
• Compare DPCM and PCM.
• Determine the output SNR of a linear delta modulation system for a 2KHz sinusoidal input signal sampled
at 64KHz. Neglect slope overload distortion and the post reconstruction filter has a bandwidth of 4KHz.
• Explain delta sigma Modulator operation with block diagram.
• Compare DM and ADM.
• A TV signal having a bandwidth of 4.2MHz is transmitted using binary PCM system. Given that the
number of quantization level is 512. Calculate(i)Codewardlength(ii)Transmission Bandwidth.
• State and prove Sampling theorem.
• What is interpolation? Explain signal reconstruction using the interpolation formula.
• State the advantages of Digital Communication.

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• What is Companding?
• How to remove the disadvantage of thresholding of coding and overloading found in Delta modulation?
• Write a note on Differential Pulse Code Modulation.
• State the difference between PCM, DPCM and Delta modulation.

• State ‘Sampling Theorem’. Discuss Nyquist Rate of sampling.

• Explain mid-rise and mid-tread type of quantizer.
• State advantages and disadvantages of digital communication over analog communication.

• Describe the effect of slope overloading and hunting in delta modulation.

• Explain various type of sampling methods.
• Discuss advantages and disadvantages of delta modulation
• Write a note on Differential Pulse Code Modulation.

• Describe the effect of slope overloading and hunting in delta modulation.

• State advantages and disadvantages of digital communication over analog communication.

5 Chapter 5: Digital Data Transmission

• For the data stream 10111001 draw the following formats. i) Polar NRZ ii)Bipolar NRZ iii) AMI NRZ
• What is scrambling? Explain scrambling and descrambling process with block diagram and suitable
example

• What is line coding? What are the ideal requirements from line coding?
• Draw the waveform of OQPSK generator for bit pattern 01101011001.
• Explain eye diagram. How ISI and other signal degradation can be studied using eye-diagram.
• Explain the applications of Eye diagram.

• Explain the properties of line codes.

• Compare: Unipolar, polar and bipolar line codes.
• Derive the power spectral density (PSD) of polar NRZ line code.
• Explain the working of regenerative repeater in digital communication system.

• Explain the cause of intersymbol interference (ISI) in digital communication systems? Explain Nyquist
criterion for zero ISI.
• Differentiate between RZ and NRZ line codes.

• Derive the Expression of quantization error.

• Why pulse shaping is required?
• Draw the block diagram of regenerative repeater and briefly explain the function of each block.
• List the advantages of digital communication over analog communication.

• Explain Time Division Multiplexing for PCM in T1 carrier systems.

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• Compare Polar, Bipolar signaling with respect to desirable properties of line codes.
• Explain companding process in PCM and state the different laws for companding.
• Explain the different type of line coding techniques with suitable diagrams.
• Explain briefly w.r.to eye diagram. (i) Sensitivity to timing Jitter (ii) Level crossing Jitter.(Timing Jitter)

• Mention Nyquist first criteria for zero ISI.

• Briefly discuss the PSD of Digital Carrier Modulation.
• What do you mean by bit scrambling.

• Compare RZ and NRZ line codes.

• What is scrambling? Draw a typical scrambler and descrambler.
• What is an Eye diagram? Explain with example.
• Explain the components of digital communication system.

• What do you understand by M-ary communication?

• Draw and explain a Regenerative Repeater in detail.
• Compare the On-off and Bipolar signaling for transmission of digital data.

• What is Line coding? Explain the different type of line coding techniques with suitable waveforms.
• Give the full forms of following: 1) ISI, 2) PSD, 3) AMI
• Draw the signals for Unipolar NRZ, Unipolar RZ, Polar NRZ, Polar RZ for Data stream 10100111.
• State the importance of Regenerative repeater in digital communication and discuss briefly about the
significance of individual components of Regenerative repeater.
• What is Inter Symbol Interference? Explain the Nyquist’s first criteria for zero ISI.
• What is scrambling? Explain scrambling and descrambling process with block diagram and suitable
example.

• Draw the signals for Unipolar NRZ, Unipolar RZ, Polar RZ for Data stream 1110000111.

6 Chapter 6: Introduction to Digital Modulation-Demodulation

Techniques
• Differentiate BPSK, QPSK and DPSK.
• For baseband pulse 110100, draw the waveforms of ASK, FSK and PSK.

• Compare binary ASK, FSK and PSK.

• Explain in brief Amplitude Shifting Keying (FSK) technique and list the applications of it.
• Explain GMSK.
• Explain BPSK modulation with neat sketch.

• Explain QPSK modulation with neat sketch.

• Compare ASK and FSK.

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• Compare Amplitude Sift Keying (ASK) with Frequency Sift Keying (FSK).
• Given modulating bit stream is 10110011. Draw the ASK, FSK and BPSK signals. Also draw the
waveforms for carrier and modulating bit stream.
• Explain Noncoherent detection of Amplitude-Shift keying (ASK) signal with necessary equations and
diagrams.
• Differentiate BPSK, QPSK and DPSK.