(SEM IV) THEORY EXAMINATION 2023-24 COMMUNICATION ENGINEERING

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.