Frequency Modulation Vs Amplitude Modulation

Frequently Asked Questions

Join ALLEN!

(Session 2026 - 27)

Name

Mobile Number

Class

Choose class

Goal

Choose your goal

Preferred Programs

Preferred Mode

State

Choose State

I agree to

I authorise ALLEN Career Institute Pvt Ltd to send me regular updates via Phone calls, Whatsapp, SMS, Robocalls (Automated Calls), Emails, or on postal address.

Frequency Modulation Vs Amplitude Modulation

1.0Introduction to Modulation

In communication systems, modulation is the process of varying a carrier signal’s property according to the message signal. Without modulation, signals cannot be transmitted efficiently over long distances.

Two major types of modulation commonly studied for JEE physics and engineering are Amplitude Modulation (AM)and Frequency Modulation (FM). Understanding their differences is crucial for solving problems in electromagnetic waves and communication systems.

2.0What is Amplitude Modulation (AM)?

Amplitude Modulation (AM) is a technique where the amplitude of the carrier wave is varied in accordance with the instantaneous amplitude of the message signal, while the frequency and phase remain constant.

Key Features of AM:

Carrier frequency: $f_{c}$
Message signal frequency: $f_{m}$
Instantaneous amplitude of AM wave: $A_{c} + A_{m} cos (2 π f_{m} t)$

Applications: AM is widely used in AM radio broadcasting, long-distance communication, and aviation communication.

Formula for AM signal:

$s (t) = [A_{c} + A_{m} cos (2 π f_{m} t)] cos (2 π f_{c} t)$

Where:

$A_{c}$ = carrier amplitude
$A_{m}$ = message signal amplitude
$f_{c}$ = carrier frequency
$f_{m}$ = message signal frequency

3.0What is Frequency Modulation (FM)?

Frequency Modulation (FM) is a technique where the frequency of the carrier wave is varied according to the instantaneous amplitude of the message signal, while amplitude remains constant.

Key Features of FM:

Frequency deviation is proportional to the message signal amplitude.
More resistant to noise compared to AM.
Requires larger bandwidth than AM.

Formula for FM signal:

$s (t) = A_{c} cos [2 π f_{c} t + 2 π k_{f} \int_{0}^{t} m (τ) d τ]$

Where:

$A_{c}$ = carrier amplitude
$f_{c}$ = carrier frequency
m(t) = message signal
$k_{f}$ = frequency sensitivity

4.0Comparison: Frequency Modulation vs Amplitude Modulation

Feature	Amplitude Modulation (AM)	Frequency Modulation (FM)
Modulation Principle	Varies amplitude of carrier	Varies frequency of carrier
Signal Characteristics	Amplitude changes, frequency constant	Frequency changes, amplitude constant
Bandwidth	Narrower, twice the message frequency	Wider, proportional to frequency deviation
Noise Immunity	Susceptible to noise	High noise immunity
Power Usage	Constant power in carrier and sidebands	Power depends on amplitude; more efficient
Applications	AM radio, aviation communication	FM radio, TV audio, high-fidelity audio

This comparison table helps JEE students quickly grasp key differences for theory and numerical problems.

5.0Mathematical Representation of AM and FM

Amplitude Modulation:

Where is the modulation index.

$s_{A M} (t) = A_{c} [1 + m cos (2 π f_{m} t)] cos (2 π f_{c} t) Where m = \frac{A _{m}}{A _{c}} is the modulation index.$

Frequency Modulation:

$s_{FM} (t) = A_{c} cos [2 π f_{c} t + β sin (2 π f_{m} t)]$

$Where β = \frac{Δ f}{f _{m}} is the modulation index (frequency deviation / message frequency).$

Observation for JEE: Modulation index determines signal spectrum, bandwidth, and deviation in transmitted signals.

6.0Advantages and Disadvantages of AM and FM

AM Advantages:

Simpler transmitter and receiver design.
Suitable for long-range transmission with less power.

AM Disadvantages:

Susceptible to noise and interference.
Lower sound quality in audio transmission.

FM Advantages:

High noise immunity; better sound quality.
Frequency deviation reduces interference.

FM Disadvantages:

Requires larger bandwidth.
More complex circuitry for transmitter and receiver.

7.0Real-Life Examples of AM and FM

AM Example: Radio stations like AM 590 kHz.
FM Example: FM 101.2 MHz for high-fidelity music broadcasting.
Other Examples:
- AM: Long-distance aviation and maritime communication.
- FM: Television audio signals, mobile radio communication.

8.0Applications of AM and FM in Communication

Amplitude Modulation:

AM radio broadcasting.
Airplane and marine communication.
Shortwave communication.

Frequency Modulation:

FM radio broadcasting.
TV audio transmission.
Two-way radio systems and telemetry.

Understanding these applications helps JEE students link theory with practical scenarios.

9.0Solved Numerical Examples

Problem 1: An AM wave has a carrier amplitude of 10 V and a modulation index of 0.5. Find the maximum and minimum amplitude of the wave.

Solution:

$A_{m a x} = A_{c} (1 + m) = 10 (1 + 0.5) = 15 V A_{m i n} = A_{c} (1 - m) = 10 (1 - 0.5) = 5 V$

Problem 2: A message signal of 3 kHz modulates a carrier of 100 MHz in FM with a frequency deviation of 5 kHz. Calculate the modulation index.

Solution:

$β = \frac{Δ f}{f _{m}} = \frac{5 kHz}{3 kHz} \approx 1.67$

Problem 3: Compare the bandwidth required for AM and FM signals if the message frequency is 5 kHz and the FM frequency deviation is 75 kHz.

Solution:

$AM bandwidth: 2 f_{m} = 2 \times 5 kHz = 10 kHz FM bandwidth (Carson’s Rule): 2 (Δ f + f_{m}) = 2 (75 + 5) = 160 kHz$

This shows FM requires significantly larger bandwidth than AM.

Frequently Asked Questions

Join ALLEN!

(Session 2026 - 27)

Name

Mobile Number

Class

Choose class

Goal

Choose your goal

Preferred Programs

Preferred Mode

State

Choose State

I agree to

I authorise ALLEN Career Institute Pvt Ltd to send me regular updates via Phone calls, Whatsapp, SMS, Robocalls (Automated Calls), Emails, or on postal address.

Frequency Modulation Vs Amplitude Modulation

1.0Introduction to Modulation

In communication systems, modulation is the process of varying a carrier signal’s property according to the message signal. Without modulation, signals cannot be transmitted efficiently over long distances.

Two major types of modulation commonly studied for JEE physics and engineering are Amplitude Modulation (AM)and Frequency Modulation (FM). Understanding their differences is crucial for solving problems in electromagnetic waves and communication systems.

2.0What is Amplitude Modulation (AM)?

Amplitude Modulation (AM) is a technique where the amplitude of the carrier wave is varied in accordance with the instantaneous amplitude of the message signal, while the frequency and phase remain constant.

Key Features of AM:

Carrier frequency: $f_{c}$
Message signal frequency: $f_{m}$
Instantaneous amplitude of AM wave: $A_{c} + A_{m} cos (2 π f_{m} t)$

Applications: AM is widely used in AM radio broadcasting, long-distance communication, and aviation communication.

Formula for AM signal:

$s (t) = [A_{c} + A_{m} cos (2 π f_{m} t)] cos (2 π f_{c} t)$

Where:

$A_{c}$ = carrier amplitude
$A_{m}$ = message signal amplitude
$f_{c}$ = carrier frequency
$f_{m}$ = message signal frequency

3.0What is Frequency Modulation (FM)?

Frequency Modulation (FM) is a technique where the frequency of the carrier wave is varied according to the instantaneous amplitude of the message signal, while amplitude remains constant.

Key Features of FM:

Frequency deviation is proportional to the message signal amplitude.
More resistant to noise compared to AM.
Requires larger bandwidth than AM.

Formula for FM signal:

$s (t) = A_{c} cos [2 π f_{c} t + 2 π k_{f} \int_{0}^{t} m (τ) d τ]$

Where:

$A_{c}$ = carrier amplitude
$f_{c}$ = carrier frequency
m(t) = message signal
$k_{f}$ = frequency sensitivity

4.0Comparison: Frequency Modulation vs Amplitude Modulation

Feature	Amplitude Modulation (AM)	Frequency Modulation (FM)
Modulation Principle	Varies amplitude of carrier	Varies frequency of carrier
Signal Characteristics	Amplitude changes, frequency constant	Frequency changes, amplitude constant
Bandwidth	Narrower, twice the message frequency	Wider, proportional to frequency deviation
Noise Immunity	Susceptible to noise	High noise immunity
Power Usage	Constant power in carrier and sidebands	Power depends on amplitude; more efficient
Applications	AM radio, aviation communication	FM radio, TV audio, high-fidelity audio

This comparison table helps JEE students quickly grasp key differences for theory and numerical problems.

5.0Mathematical Representation of AM and FM

Amplitude Modulation:

Where is the modulation index.

$s_{A M} (t) = A_{c} [1 + m cos (2 π f_{m} t)] cos (2 π f_{c} t) Where m = \frac{A _{m}}{A _{c}} is the modulation index.$

Frequency Modulation:

$s_{FM} (t) = A_{c} cos [2 π f_{c} t + β sin (2 π f_{m} t)]$

$Where β = \frac{Δ f}{f _{m}} is the modulation index (frequency deviation / message frequency).$

Observation for JEE: Modulation index determines signal spectrum, bandwidth, and deviation in transmitted signals.

6.0Advantages and Disadvantages of AM and FM

AM Advantages:

Simpler transmitter and receiver design.
Suitable for long-range transmission with less power.

AM Disadvantages:

Susceptible to noise and interference.
Lower sound quality in audio transmission.

FM Advantages:

High noise immunity; better sound quality.
Frequency deviation reduces interference.

FM Disadvantages:

Requires larger bandwidth.
More complex circuitry for transmitter and receiver.

7.0Real-Life Examples of AM and FM

AM Example: Radio stations like AM 590 kHz.
FM Example: FM 101.2 MHz for high-fidelity music broadcasting.
Other Examples:
- AM: Long-distance aviation and maritime communication.
- FM: Television audio signals, mobile radio communication.

8.0Applications of AM and FM in Communication

Amplitude Modulation:

AM radio broadcasting.
Airplane and marine communication.
Shortwave communication.

Frequency Modulation:

FM radio broadcasting.
TV audio transmission.
Two-way radio systems and telemetry.

Understanding these applications helps JEE students link theory with practical scenarios.

9.0Solved Numerical Examples

Problem 1: An AM wave has a carrier amplitude of 10 V and a modulation index of 0.5. Find the maximum and minimum amplitude of the wave.

Solution:

$A_{m a x} = A_{c} (1 + m) = 10 (1 + 0.5) = 15 V A_{m i n} = A_{c} (1 - m) = 10 (1 - 0.5) = 5 V$

Problem 2: A message signal of 3 kHz modulates a carrier of 100 MHz in FM with a frequency deviation of 5 kHz. Calculate the modulation index.

Solution:

$β = \frac{Δ f}{f _{m}} = \frac{5 kHz}{3 kHz} \approx 1.67$

Problem 3: Compare the bandwidth required for AM and FM signals if the message frequency is 5 kHz and the FM frequency deviation is 75 kHz.

Solution:

$AM bandwidth: 2 f_{m} = 2 \times 5 kHz = 10 kHz FM bandwidth (Carson’s Rule): 2 (Δ f + f_{m}) = 2 (75 + 5) = 160 kHz$

This shows FM requires significantly larger bandwidth than AM.

Frequently Asked Questions

1

What is the main difference between AM and FM?

2

Which modulation is more resistant to noise?

3

Which one requires more bandwidth?

4

What are the practical applications of AM?

5

What are the practical applications of FM?

Join ALLEN!

Frequency Modulation Vs Amplitude Modulation

1.0Introduction to Modulation

2.0What is Amplitude Modulation (AM)?

3.0What is Frequency Modulation (FM)?

4.0Comparison: Frequency Modulation vs Amplitude Modulation

5.0Mathematical Representation of AM and FM

6.0Advantages and Disadvantages of AM and FM

7.0Real-Life Examples of AM and FM

8.0Applications of AM and FM in Communication

9.0Solved Numerical Examples

Table of Contents

Frequently Asked Questions

1

What is the main difference between AM and FM?

2

Which modulation is more resistant to noise?

3

Which one requires more bandwidth?

4

What are the practical applications of AM?

5

What are the practical applications of FM?

Join ALLEN!

Frequency Modulation Vs Amplitude Modulation

1.0Introduction to Modulation

2.0What is Amplitude Modulation (AM)?

3.0What is Frequency Modulation (FM)?

4.0Comparison: Frequency Modulation vs Amplitude Modulation

5.0Mathematical Representation of AM and FM

6.0Advantages and Disadvantages of AM and FM

7.0Real-Life Examples of AM and FM

8.0Applications of AM and FM in Communication

9.0Solved Numerical Examples

Table of Contents