Why Is Modulation Necessary in Communication Systems?
Nowadays, information, messages, data, and signals are sent from one location to another within seconds. How is such fast transmission possible? The communication system uses modulation to enhance the range of the signals. Most of the signals generated in daily life are sinusoidal waveforms. Sinusoidal wave is a curve that describes smooth repetitive oscillations. The signals transferred during communication include crucial information in the form of a sinusoidal wave. Modulation and its types play a crucial role in the rapid transmission of the signals from the sender to the receiver. Modulation is the superimposition of the signal wave (carrying the message) with a high-frequency carrier signal to ensure faster transmission of the signal.
What is Modulation And Its Types?
Modulation is one of the crucial branches of electronics science that is widely used in communication systems. It includes the different fundamental properties of the signal to transpose it from one location to another.
Types of Signals used in the Modulation
Modulating Signal: This is the signal that contains the message to be transmitted from the sender to the receiver and is called a message signal. Generally, the message signals are the band of low or high frequencies and are often called baseband signals. The message signals are the signals to be transmitted from the sender to the receiver. The frequency of the message signals to be sent is generally low. Thus, these signals undergo modulation to get correctly transmitted from one location to another.
Carrier Signal: The other signal used in the process of modulation is the carrier signal that has high-frequency sinusoidal waves. The high-frequency carrier wave can travel much quicker as compared to the baseband signal. These signals have a specific frequency, amplitude, and phase, but no information. After modulation, carrier signals are used to transmit the signal to the receiver.
Modulated Signal: After the modulation is done, the resultant signal refers to the modulated signal. This signal is the mixture of the carrier signal and message signal.
(Image to be added soon)
The diagram shows three types of signals, namely, message signal, carrier signal, and modulated signal that is the mixture of the message and carrier signal.
What Are The Types Of Modulation?
There are generally three types of modulation:
Amplitude Modulation: By superimposing the base signal with the carrier signal having a different amplitude, but the same frequency, if the amplitude of the base signal modifies or modulates, then it is said to be amplitude modulation.
(Image to be added soon)
The diagram shows the amplified modulated wave after superimposing the message signal with the carrier signal.
Phase Modulation: It is the type of modulation in which the phase of the base signal changes while superimposing it with a carrier signal.
Frequency Modulation: By superimposing the base signal with the carrier signal having a different frequency, but the same amplitude, if the frequency of the base signal modifies or modulates, then it is said to be frequency modulation.
What is the Need for Modulation?
Increase The Signal Strength
The baseband signals transmitted by the sender are not capable of direct transmission. The strength of the message signal should be increased so that it can travel longer distances. This is where modulation is essential. The most vital need of modulation is to enhance the strength of the signal without affecting the parameters of the carrier signal.
Wireless Communication System
Modulation has removed the necessity for using wires in the communication systems. It is because modulation is widely used in transmitting signals from one location to another with faster speed. Thus, the modulation technique has helped in enhancing wireless communication systems.
Prevention Of Message Signal From Mixing
Modulation and its types prevent the interference of the message signal from other signals. It is because a person sending a message signal through the phone cannot tell such signals apart. As a result, they will interfere with each other. However, by using carrier signals having a high frequency, the mixing of the signals can be prevented. Thus, modulation ensures that the signals received by the receiver are entirely perfect.
Size Of The Antenna
The signals within 20 Hz to 20 kHz frequency range can travel only a few distances. To send the message signal, the length of the antenna should be a quarter wavelength of the used frequency. Thus, modulation is required to increase the frequency of the message signal and to enhance its strength to reach the receiver.
Length of the antenna can be easily calculated using this formula:
L = λ = u/ν
= (3 x 108) / ν
Here, L = length of antenna
λ = wavelength of the transmitted signal
ν = carrier wave frequency
What are the Uses of Modulation?
One of the most common uses of different types of modulation is the inter-conversion of signals from its existing to another form.
Digital Modulation is used for the transmissions of the digital signals over analog baseband.
Analog Modulation is used to transfer the low bandwidth signals such as TV or radio signals over a higher bandwidth.
Modern modulation techniques are widely used to carry out FDM, that is, Frequency Division Multiplexing
FAQs on Need for Modulation in Physics Explained
1. What is modulation in the context of communication systems?
In communication systems, modulation is the process of superimposing a low-frequency message signal, which contains the information to be sent, onto a high-frequency carrier wave. This process modifies a property of the carrier wave (like its amplitude, frequency, or phase) in accordance with the message signal, making it suitable for long-distance transmission.
2. What are the three primary reasons we need modulation for signal transmission?
Modulation is essential for effective communication for several key reasons, as per the CBSE 2025-26 syllabus. The main needs are:
- Reduction of Antenna Size: To efficiently radiate a signal, the antenna size should be comparable to the signal's wavelength (typically λ/4). Low-frequency signals have very long wavelengths, requiring impractically large antennas. Modulation shifts the signal to a higher frequency, reducing the wavelength and allowing for practical, smaller antennas.
- Avoiding Signal Mixing: Without modulation, if multiple sources transmitted signals in the same low-frequency range (e.g., audio), they would all mix and become indistinguishable. Modulation allows different signals to be assigned unique high-frequency carrier waves, a technique called Frequency Division Multiplexing (FDM), so they don't interfere.
- Increasing the Range of Communication: Low-frequency signals have low energy and are quickly attenuated (weakened) by the medium, limiting their range. High-frequency carrier waves have higher energy and can travel much longer distances without significant loss of strength.
3. How does modulation solve the practical problem of antenna size?
The relationship between an antenna's required length (L), the speed of light (c), and the signal's frequency (f) is based on the wavelength (λ), where L is proportional to λ and λ = c/f. A low-frequency audio signal, say 20 kHz, would require an antenna several kilometres long, which is impractical. By modulating this 20 kHz signal onto a 1 MHz (1,000,000 Hz) carrier wave, the frequency is increased 50 times. This drastically reduces the required wavelength and, consequently, the antenna size to a few meters, making transmission feasible.
4. What are the main types of continuous-wave modulation, and how do they differ?
The three main types of continuous-wave (or analog) modulation are based on which property of the high-frequency carrier wave is varied:
- Amplitude Modulation (AM): The amplitude of the carrier wave is varied in proportion to the instantaneous amplitude of the message signal, while its frequency and phase remain constant.
- Frequency Modulation (FM): The frequency of the carrier wave is varied in proportion to the instantaneous amplitude of the message signal, while its amplitude and phase remain constant.
- Phase Modulation (PM): The phase of the carrier wave is varied in proportion to the instantaneous amplitude of the message signal, while its amplitude and frequency remain constant.
5. Why can't low-frequency baseband signals be transmitted directly over long distances through space?
Low-frequency signals, often called baseband signals (like voice or music), cannot be transmitted directly over long distances for two main reasons. First, they possess very low energy and are therefore heavily attenuated or absorbed by the atmosphere, causing them to lose strength rapidly. Second, due to their long wavelengths, they cannot be efficiently radiated by a practical-sized antenna, leading to extremely poor signal propagation into space.
6. How does modulation allow multiple radio stations to broadcast simultaneously without interfering with each other?
Modulation enables a technique called Frequency Division Multiplexing (FDM). Each radio station is allocated a unique, specific carrier frequency by regulatory authorities. The station modulates its audio program (the message signal) onto its assigned carrier wave. Although all stations' final modulated signals travel through the same space, they occupy different frequency bands. A radio receiver can then be tuned to select the specific carrier frequency of the desired station, filtering out all others and preventing interference.
7. What is the difference between a message signal, a carrier signal, and a modulated signal?
These three signals are the fundamental components in the modulation process:
- The Message Signal (or Baseband Signal) is the original low-frequency signal that contains the information to be transmitted (e.g., audio, video, or data).
- The Carrier Signal is a high-frequency, single-frequency sinusoidal wave. It contains no information and acts as a 'vehicle' to carry the message signal over long distances.
- The Modulated Signal is the final signal that results from the modulation process. It is the carrier wave whose characteristics (amplitude, frequency, or phase) have been altered by the message signal. This is the signal that is actually transmitted.
8. Can you provide a real-world example that perfectly illustrates the importance of modulation?
A perfect real-world example is FM radio broadcasting. An FM station wants to transmit a song, which is an audio signal with frequencies from 20 Hz to 20 kHz. Transmitting this low-frequency signal directly is impossible due to the need for a massive antenna and severe signal loss. Instead, the station uses frequency modulation to impose this audio signal onto its assigned high-frequency carrier wave, for example, 98.3 MHz. This allows the signal to be broadcast for many miles from a reasonably sized antenna and enables your car radio to tune specifically to 98.3 MHz to listen to that song without hearing interference from a station at 101.1 MHz.
