About this previous year paper
This document is the B.Tech (Semester IV) Theory Examination Question Paper for the subject BEC401 – Communication Engineering, conducted in the academic year 2023–2024.
It is a 3-hour, 70-mark examination designed to test students on the fundamentals of analog and digital communication, modulation techniques, noise analysis, sampling theory, and modern digital modulation methods.
The exam is divided into three sections—A, B, and C—covering conceptual, analytical, and diagram-based questions.
SECTION A – Short Answer Questions (14 Marks)
Seven short 2-mark questions cover essential communication engineering concepts:
Need for modulation
Efficiency of an AM system at 100% modulation
Effect of modulating signal amplitude on FM bandwidth
Definition of figure of merit
Disadvantages of delta modulation
Nyquist rate & interval for x(t) = 20 sin(100πt) cos(200πt)
Difference between PSK and DPSK
This section evaluates theoretical understanding and formula-based reasoning.
SECTION B – Intermediate Analytical & Diagram Questions (21 Marks)
Students must attempt any three from the following:
Block diagram of a communication system + modulation index calculation
FM demodulation using Phase Locked Loop (PLL)
Figure of merit for DSB-SC system
Block diagram of PCM transmitter and receiver
Detailed explanation of Quadrature Amplitude Modulation (QAM)
These questions test diagram-based understanding and analytical skills.
SECTION C – Long/Advanced Questions (28 Marks)
Each main question includes two parts; students must attempt one from each.
3. Amplitude Modulation & DSB-SC
Numerical AM problem:
Message amplitude
Sideband amplitude
Total power delivered
Carrier power
Transmission efficiency
Working of a Ring Modulator for DSB-SC generation
4. Frequency Modulation Concepts
Need for Pre-emphasis & De-emphasis in FM
FM generation using AM wave and reverse process (with block diagram)
5. Multiplexing & Delta Modulation
Time Division Multiplexing (TDM) with block diagram
Working of Delta Modulator with diagram
6. Noise & Quantization
Types of noise in communication systems
Proof that SQNR(dB) = 1.8 + 6R for PCM signals
7. Digital Modulation Techniques
Amplitude Shift Keying (ASK)
Waveforms
Modulator/demodulator block diagram
Short note on Minimum Shift Keying (MSK)
This section tests deeper understanding of analog/digital systems, mathematical analysis, and communication system design.
Overall Purpose of the Document
The purpose of this exam paper is to evaluate a student's knowledge and skills in communication engineering, including:
Analog modulation (AM, FM)
Digital modulation (ASK, PSK, DPSK, MSK, QAM)
Sampling, quantization, and PCM
Demodulation techniques (PLL, delta modulation)
Multiplexing methods
Noise types and performance measures
Mathematical analysis of communication signals
The paper integrates numerical questions, theoretical explanations, block diagrams, waveform analysis, and conceptual understanding to ensure complete assessment.