JEE Communication Systems - Previous Year Questions (2009-2024)

📡 Chapter Overview

Communication Systems represents the practical application of electromagnetic waves and modern electronics, contributing 4-5% weightage in JEE Physics. This compilation provides comprehensive coverage of 15 years of JEE Previous Year Questions (2009-2024) in Communication Systems, systematically organized for focused preparation.

📊 Comprehensive Analysis

Chapter Statistics

📈 Overall Performance Metrics:
Total Questions (2009-2024): 65+
Average Questions per Year: 4-5
Difficulty Level: Easy to Medium
Success Rate: 60-70%

Question Type Distribution:
- Multiple Choice Questions: 46 (71%)
- Integer Type: 14 (22%)
- Paragraph Questions: 3 (4%)
- Match the Columns: 2 (3%)

Topic Distribution:
- Modulation and Demodulation: 30%
- Transmission Media: 25%
- Antennas and Wave Propagation: 20%
- Digital Communication: 15%
- Modern Communication Systems: 10%

Year-wise Trend Analysis

📅 Difficulty Evolution:

2009-2012 (IIT-JEE Era):
- Average Difficulty: Medium
- Focus: Basic communication concepts
- Pattern: Formula-based questions
- Key Topics: Modulation, Antenna theory

2013-2016 (JEE Advanced Transition):
- Average Difficulty: Easy-Medium
- Focus: Conceptual understanding
- Pattern: Application-oriented
- Key Topics: Digital communication, Modern systems

2017-2020 (Stabilization Period):
- Average Difficulty: Easy
- Focus: Practical applications
- Pattern: Real-world emphasis
- Key Topics: Mobile communication, Internet

2021-2024 (Digital Era):
- Average Difficulty: Easy-Medium
- Focus: Modern communication tech
- Pattern: Current technology emphasis
- Key Topics: 5G, Satellite communication

🎯 Detailed Topic Coverage

1. Modulation and Demodulation

Concept Foundation

🔬 Key Concepts:
- Need for modulation
- Amplitude modulation (AM)
- Frequency modulation (FM)
- Phase modulation (PM)
- Modulation index
- Sidebands and bandwidth
- Demodulation techniques
- Superheterodyne receiver

Question Pattern Analysis

📋 Question Distribution:
Amplitude Modulation: 35%
- Modulation index calculations
- Sideband analysis
- Power distribution
- AM transmitter/receiver

Frequency Modulation: 25%
- Frequency deviation
- Modulation index
- Carson's rule
- FM bandwidth

Modulation Theory: 20%
- Need for modulation
- Comparison of techniques
- Advantages/disadvantages
- Applications

Demodulation: 20%
- Detection techniques
- Superheterodyne principle
- Receiver sensitivity
- Noise considerations

Sample Questions with Detailed Solutions

Example 1 (AM Modulation Index, 2021)

Q: An AM transmitter has maximum voltage of 100V and minimum voltage of 20V. Find the modulation index.

Solution:
Given: Vmax = 100V, Vmin = 20V

Modulation index: m = (Vmax - Vmin)/(Vmax + Vmin)
m = (100 - 20)/(100 + 20) = 80/120 = 2/3 ≈ 0.667

The modulation index is 0.667 or 66.7%

Key Concept: AM modulation index formula

Example 2 (FM Bandwidth, 2022)

Q: An FM transmitter has maximum frequency deviation of 75kHz and modulating signal frequency of 15kHz. Find the bandwidth using Carson's rule.

Solution:
Given: Δf = 75kHz, fm = 15kHz

Modulation index: β = Δf/fm = 75/15 = 5

Carson's rule: BW = 2(Δf + fm) = 2(75 + 15) = 2 × 90 = 180kHz

The FM signal bandwidth is 180kHz

Key Concept: Carson's rule for FM bandwidth

Example 3 (AM Power Distribution, 2023)

Q: An AM transmitter has carrier power of 10kW and modulation index of 0.8. Find the total transmitted power and power in each sideband.

Solution:
Given: Pc = 10kW, m = 0.8

Total power: Pt = Pc(1 + m²/2) = 10(1 + 0.8²/2) = 10(1 + 0.64/2) = 10(1 + 0.32) = 13.2kW

Power in each sideband: Psb = Pc × m²/4 = 10 × 0.8²/4 = 10 × 0.64/4 = 1.6kW

Total sideband power = 2 × 1.6 = 3.2kW

Key Concept: Power distribution in AM signals

2. Transmission Media and Wave Propagation

Concept Foundation

🔬 Key Concepts:
- Transmission lines
- Waveguides
- Fiber optics
- Propagation modes
- Attenuation and distortion
- Line impedance
- Standing waves
- Reflection coefficient

Question Pattern Analysis

📋 Question Distribution:
Transmission Lines: 30%
- Characteristic impedance
- Propagation constant
- Standing wave ratio
- Line losses

Wave Propagation: 25%
- Ground wave propagation
- Sky wave propagation
- Line of sight propagation
- Frequency bands

Fiber Optics: 20%
- Total internal reflection
- Attenuation in fibers
- Fiber types
- Bandwidth considerations

Antennas: 25%
- Antenna parameters
- Radiation patterns
- Gain and directivity
- Antenna types

Sample Questions with Detailed Solutions

Example 1 (Antenna Height, 2021)

Q: Find the height of a TV transmitting antenna required to cover a range of 80km. Assume Earth's radius is 6400km.

Solution:
Given: Range = 80km = 80,000m, R = 6400km = 6.4 × 10⁶m

For line of sight propagation: Range = √(2Rh)
h = Range²/(2R) = (80,000)²/(2 × 6.4 × 10⁶)
h = 6.4 × 10⁹/(12.8 × 10⁶) = 500m

The antenna height should be approximately 500m

Key Concept: Line of sight propagation range calculation

Example 2 (Fiber Optic Attenuation, 2022)

Q: An optical fiber has attenuation of 0.5 dB/km. If input power is 1mW, find the output power after 20km.

Solution:
Given: α = 0.5 dB/km, L = 20km, Pin = 1mW

Total attenuation: α_total = α × L = 0.5 × 20 = 10dB

Output power: Pout = Pin × 10^(-α_total/10)
Pout = 1mW × 10^(-10/10) = 1mW × 10^(-1) = 0.1mW

The output power after 20km is 0.1mW

Key Concept: Fiber optic attenuation calculation

Example 3 (Standing Wave Ratio, 2023)

Q: A transmission line has maximum voltage of 100V and minimum voltage of 20V. Find the reflection coefficient and VSWR.

Solution:
Given: Vmax = 100V, Vmin = 20V

Voltage Standing Wave Ratio: VSWR = Vmax/Vmin = 100/20 = 5

Reflection coefficient: Γ = (VSWR - 1)/(VSWR + 1) = (5 - 1)/(5 + 1) = 4/6 = 2/3 ≈ 0.667

Key Concept: VSWR and reflection coefficient relationship

3. Digital Communication

Concept Foundation

🔬 Key Concepts:
- Analog to digital conversion
- Sampling theorem
- Pulse code modulation
- Digital modulation techniques
- ASK, FSK, PSK
- Error detection and correction
- Data compression
- Computer networks

Question Pattern Analysis

📋 Question Distribution:
Digital Modulation: 30%
- ASK, FSK, PSK techniques
- Bandwidth requirements
- Advantages over analog
- Applications

Pulse Modulation: 25%
- Pulse amplitude modulation
- Pulse width modulation
- Pulse position modulation
- PCM systems

Sampling and Quantization: 25%
- Nyquist theorem
- Sampling rate
- Quantization error
- Signal to noise ratio

Digital Communication: 20%
- Computer networks
- Internet protocols
- Data transmission
- Modern applications

Sample Questions with Detailed Solutions

Example 1 (Sampling Theorem, 2021)

Q: A voice signal has frequency range from 300Hz to 3400Hz. Find the minimum sampling rate required.

Solution:
Given: Highest frequency fm = 3400Hz

According to Nyquist theorem: fs ≥ 2fm
Minimum sampling rate: fs_min = 2 × 3400 = 6800 Hz

The minimum sampling rate required is 6.8 kHz

In practice, standard telephone systems use 8 kHz sampling rate

Key Concept: Nyquist sampling theorem

Example 2 (Quantization Levels, 2022)

Q: A PCM system uses 8-bit quantization for signals ranging from -5V to +5V. Find the quantization step size and maximum quantization error.

Solution:
Given: Voltage range = ±5V = 10V total, n = 8 bits

Number of quantization levels: L = 2^8 = 256

Quantization step size: Δ = Range/L = 10V/256 = 0.039V ≈ 39mV

Maximum quantization error: Δ/2 = 19.5mV

Key Concept: PCM quantization and error

Example 3 (Digital Modulation Bandwidth, 2023)

Q: Compare the bandwidth requirements of ASK and FSK systems if the data rate is 1kbps and FSK uses carriers separated by 2kHz.

Solution:
Given: Data rate R = 1kbps = 1000 bps, Frequency separation = 2kHz

For ASK: Bandwidth ≈ 2R = 2 × 1000 = 2000 Hz = 2kHz

For FSK: Bandwidth ≈ 2R + frequency separation = 2 × 1000 + 2000 = 4000 Hz = 4kHz

FSK requires twice the bandwidth of ASK for the same data rate

Key Concept: Digital modulation bandwidth comparison

4. Modern Communication Systems

Concept Foundation

🔬 Key Concepts:
- Satellite communication
- Mobile communication
- Internet and data communication
- RADAR systems
- GPS and navigation
- Modern wireless technologies
- 5G communication
- IoT applications

Sample Questions with Detailed Solutions

Example 1 (Satellite Communication, 2021)

Q: A communication satellite is in geostationary orbit at height 35786km above Earth's surface. Find the round-trip time delay for a signal.

Solution:
Given: Height h = 35786km

Round-trip distance: 2h = 2 × 35786 = 71572km
Speed of light: c = 3 × 10⁵ km/s

Time delay: t = distance/speed = 71572/(3 × 10⁵) = 0.239s

The round-trip time delay is approximately 239ms

Key Concept: Satellite communication delay

Example 2 (Mobile Communication, 2022)

Q: A mobile communication system operates at 900MHz with cell radius of 5km. Assuming hexagonal cells, find the number of cells required to cover an area of 10000km².

Solution:
Given: Cell radius r = 5km, Total area = 10000km²

Area of hexagonal cell: A_cell = (3√3/2) × r² = 2.598 × 25 = 64.95km²

Number of cells: N = Total area / Cell area = 10000/64.95 ≈ 154 cells

Approximately 154 cells are required

Key Concept: Cellular network planning

🎓 Advanced Problem Solving Strategies

Problem Classification and Approach

🧠 Strategic Problem Solving:

Type 1: Direct Formula Application (Easy)
- Identify the appropriate formula
- Check communication parameters
- Substitute values carefully
- Verify units and results

Type 2: System Analysis (Medium)
- Understand the communication system
- Apply system principles
- Calculate performance parameters
- Check practical constraints

Type 3: Design Problems (Hard)
- Understand requirements
- Apply design principles
- Choose appropriate parameters
- Verify system performance

Common Mistakes and Corrections

⚠️ Critical Mistakes to Avoid:

1. Modulation Index:
   Wrong: Confusing AM and FM modulation indices
   Correct: Use appropriate formulas for each modulation type

2. Bandwidth Calculations:
   Wrong: Using simple 2× rule for all modulation types
   Correct: Use specific bandwidth formulas for each modulation

3. Sampling Theorem:
   Wrong: Using exactly 2× instead of greater than 2×
   Correct: Sampling rate must be greater than 2× maximum frequency

4. Power Calculations:
   Wrong: Ignoring sideband power distribution
   Correct: Account for carrier and sideband power separately

System Design Considerations

🔬 Design Principles:

1. Modulation Selection:
   - Consider bandwidth requirements
   - Evaluate power efficiency
   - Assess complexity vs performance
   - Match to application requirements

2. Transmission Planning:
   - Calculate link budget
   - Consider path losses
   - Account for noise and interference
   - Design for reliability

3. System Optimization:
   - Balance cost and performance
   - Consider future expansion
   - Maintain compatibility
   - Ensure scalability

📈 Performance Metrics and Analysis

Success Rate by Topic

📊 Topic-wise Success Rate:

High Success (>75%):
- Basic modulation calculations
- Simple antenna problems
- Sampling theorem applications
- Direct formula applications

Medium Success (55-75%):
- Communication system analysis
- Digital communication concepts
- Transmission line problems
- Modern communication systems

Low Success (<55%):
- Complex system design
- Advanced modulation techniques
- Network analysis
- Integration problems

Year-wise Difficulty Trends

📈 Difficulty Evolution:

2020-2024: Easy to Medium
- Focus on modern applications
- Current technology emphasis
- Practical problem solving
- Real-world relevance

2015-2019: Easy to Medium
- Standard problem types
- Balanced concepts
- Application orientation

2009-2014: Medium
- Mathematical emphasis
- Traditional communication
- Theoretical concepts

🚀 Preparation Strategies

Study Schedule

📅 Recommended Study Plan:

Week 1: Modulation Basics
- Need for modulation
- AM principles and calculations
- FM principles and applications
- Comparison of techniques

Week 2: Transmission Media
- Transmission lines
- Wave propagation
- Antenna fundamentals
- Fiber optic basics

Week 3: Digital Communication
- Sampling theorem
- PCM and digital modulation
- Error detection
- Data communication

Week 4: Modern Systems
- Satellite communication
- Mobile communication
- Internet protocols
- Modern applications

Week 5: Integration and Practice
- System design problems
- Previous year questions
- Mock tests
- Current technology updates

Key Formulas to Remember

📋 Essential Formula Sheet:

Modulation:
- AM modulation index: m = (Vmax - Vmin)/(Vmax + Vmin)
- AM total power: Pt = Pc(1 + m²/2)
- FM modulation index: β = Δf/fm
- FM bandwidth (Carson's rule): BW = 2(Δf + fm)

Transmission:
- Antenna range: d = √(2Rh)
- VSWR: VSWR = Vmax/Vmin
- Reflection coefficient: Γ = (VSWR - 1)/(VSWR + 1)
- Fiber attenuation: Pout = Pin × 10^(-αL/10)

Digital Communication:
- Nyquist rate: fs ≥ 2fm
- Quantization step: Δ = Range/2^n
- Maximum quantization error: Δ/2
- Digital ASK bandwidth: BW ≈ 2R

Satellite Communication:
- Round-trip delay: t = 2h/c
- Path loss: L = 20log₁₀(4πd/λ)

🏆 Summary and Key Takeaways

Essential Concepts to Master

✨ Must-Know Concepts:

1. Modulation Techniques (AM, FM, PM)
2. Transmission Media and Wave Propagation
3. Antenna Theory and Applications
4. Digital Communication Principles
5. Sampling and Quantization
6. Modern Communication Systems
7. Satellite and Mobile Communication
8. Internet and Network Protocols

Exam Strategy

🎯 Exam Day Approach:

1. Question Analysis:
   - Identify communication concept
   - Determine appropriate formula
   - Check given parameters
   - Plan solution approach

2. Problem Solving:
   - Apply correct formulas
   - Use practical approximations
   - Maintain unit consistency
   - Verify physical reasonableness

3. Time Management:
   - Allocate 4-5 minutes per question
   - Focus on high-scoring topics
   - Attempt all easy questions
   - Review if time permits

Master JEE Communication Systems with systematic preparation and comprehensive previous year question practice! 📡

Remember: Communication Systems questions are often straightforward with clear applications. Focus on understanding the fundamental principles and their real-world applications in modern technology! ✨