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Modulation refers to the process of encoding information in a signal, while demodulation refers to the process of extracting information from a transmitted signal. To establish reliable communication over a considerable distance, the message carrying signal requires a high-frequency signal, whose properties should not be altered based on the message carrier signal. The frequency of a radio frequency channel is the frequency of a carrier wave. A carrier wave is formed of a constant frequency.
Read More: Radio Waves
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Key Terms: Modulation, Demodulation, MODEM, Amplitude, Electrical Signals, Modulation Phase, Modulation Amplitude
What is Modulation And Demodulation?
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Modern communication systems are composed of several components that work together all day long in a comprehensive way. Modulator and demodulator (MODEM), a paired system, is responsible for revolutionizing the global communication scenario.
What is Modulation?
The process of varying an RF carrier wave as per the information in a low-frequency signal is known as modulation.
| Modulation is the method that superimposes low-frequency signals over high-frequency carrier signals. |
- The message contained in the message signal changes if the characteristics of the message signal are changed.
- In addition, a signal traveling at a high frequency can cover a greater distance without being affected by external disturbances.
- In order to transmit the message signal, we generally use a high-frequency signal called a carrier signal. The process is referred to as modulation.
- An example of modulation is when the parameter values of the carrier signal are changed according to the values of the modulating signal at a given instant.
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|---|---|---|
| Sky Wave Propagation | Space Travel Equipment | Electromagnetic Waves MCQ |
| Terms Used for Electronic Communication Systems | Internet | Pulse Width Modulation |
Working of Modulation
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The working principle of Modulation is as follows:
- During modulation, data is converted into electrical signals or optical carrier signals that are optimized for transmission. Carrier waves are of a constant frequency, similar to a sine wave.
- For a wide range of applications, we need to adjust the signal to higher recurrence bands, which are referred to as Radio Frequency (RF) bands, in order to suit the spread characteristics of correspondence channels.
- Non-dispersive channels provide the simplest RF bands since they alter signal amplitude and period as the message is transmitted. Non-dispersive channels can be demodulated in two different ways.
- The first path involves measuring phase bending and using a coordinated filter as in a baseband correspondence framework.
- Sound demodulation refers to the process of identifying frequencies.
- The second method, which we call non-coherent demodulation, does not use phase data at all in the demodulation process.
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Types of Modulations
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Modulation can be broken down into three different types:
- Frequency Modulation: Frequency modulation occurs when a signal's amplitude and frequency have a constant state, but the carrier wave frequency changes or varies.
- Phase Modulation: Phase modulation refers to a situation where the phase of a high-frequency carrier wave varies or changes due to a phase shift in the modulated signal, while the amplitude and frequency remain unchanged.
- Amplitude Modulation: Amplitude modulation refers to a change in the amplitude of a carrier wave caused by a change in the modulation of the signal. The signal phase and frequency remain constant.
![Types of Modulations]()
Types of Modulations
| Example: What is the mechanism for Modulation? Solution: There are a few primary modulation mechanisms that are categorized in an appropriate manner for practical purposes. Mechanisms of modulation can be divided into 4 general categories:
The direct transfer of the baseband signal is not possible. Therefore, to transmit such a signal to a greater distance, the signal strength should increase, which does not affect any parameter of the signal. |
Advantages of Modulation
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Here are the advantages of the modulation-
- Modulation helps to reduce the size of the antenna.
- In the case of Modulation, signals do not get mixed up.
- It increases the communication ranges.
- Necessary adjustments in the bandwidth signal can be done in modulation.
- It also improves the reception quality.
Need For Modulation
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In the basic system of a baseband signal, which has not been moduled or demodulated, the frequency can be either mixed up or the range of frequency is lower. This can lead to interruptions in communication. Therefore, here are the basic needs for the modulations.
- Modulation solved these issues by providing clear and long-ranged frequencies.
- Also, modulation provides unaffected parameters of the signal.
- Modulation can also lower the complications of the whole communication process.
What is Demodulation?
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When data modulated carrier waves are demodulated, you get their original form. It is a demodulator signal circuit that actually recovers data from a modulator carrier wave. Demodulators come in different types as well. Demodulators output signals that are generally described as audio, binary data, or pictures.
Read More: Difference Between Analog and Digital Signals
Need For Demodulation
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Demodulation helps to extract information from modulated carrier waves. Waves of radio frequencies containing modulated audio frequencies are carried within wireless signals.
- It is impossible for the diaphragm of a telephone receiver to vibrate when a high frequency is involved.
- In addition, the human ear is not able to hear this frequency. In order to distinguish the audio frequencies from the radio waves, a demodulator must be applied.
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Differences Between Modulation and Demodulation
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The differences between Modulation and Demodulation are as follows:
| Modulation | Demodulation |
|---|---|
| Data is collected and modified onto the carrier. | Data is recovered. |
| Modulation is carried out on the sender’s side. | Demodulation takes place on the receiver’s side. |
| Modulation is a process in which the original message signal is mixed with a carrier wave whose parameters need to be altered. | Demodulation takes place in order to create an original information signal by separating the carrier signal from the message signal. |
| Modulation is done to transmit data over longer distances. | Demodulation is the process that prevents the signal from being modified. |
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| Related Topic | ||
|---|---|---|
| Optical Fiber | Electromagnetic Spectrum | Electromagnetic Pulse |
| Remote Sensing | Bandwidth of a Signal | X- Rays |
| Space wave propagation | Transducer | Ground Wave Propagation |
Things to Remember
- Modulation and Demodulation represent one of the most important components of the communication system.
- Modulation is the process of modifying the message source into a format that is suitable for transmission.
- Demodulation is the process of decoding the modulated signal into its original form.
- The three types of modulation are Amplitude, Frequency, and Phase modulation.
- There are four types of modulation mechanisms: Analog Modulation, Digital Modulation, Pulse Modulation, and Spread Spectrum Modulation.
Previous Year Questions
- Sky wave propagation is used in…. (VITEEE 2011)
- The frequency of an FM transmitter without signal input is called…. (VITEEE 2011)
- The attenuation in optical fibre is mainly due to…. (VITEEE 2010)
- Sinusoidal carrier voltage of frequency 1.5MHz and amplitude 50V is…. (VITEEE 2010)
- In amplitude modulation, the amplitude of carrier wave is… (VITEEE 2019)
- Amplitude modulation has… (KCET 2015)
- The process of superimposing message signal on high frequency carrier wave…(KCET 2016)
- The radius of the Earth is 6400 km. If the height of an antenna is…. (KTET 2018)
- A basic communication system consists of… (KTET 2017)
- An antenna uses electromagnetic waves of frequency…. (KTET 2019)
- In frequency modulation… (KEAM)
- A ground receiver receives a signal at 5MHz… .(KEAM)
- Advantages of optical fibre communications over two wire transmission… (GUJCET 2008)
- The layer in earth's atmosphere which reflects radio waves from the earth… (COMEDK UGET 2012)
- The TV signals have a bandwidth of 3.7MHz. The number of TV channels… (COMEDK UGET 2014)
- The increase in the height of the tower of height 200 m to get its coverage range… (COMEDK UGET 2014)
- The wireless communication frequency bands for Cellular Mobile Radio… (COMEDK UGET 2015)
- Amplitude modulation is the process of… (JKCET 2017)
- In television transmission what type of modulation is used… (JKCET 2012)
- For an amplitude modulated wave the maximum amplitude is found… (AMUEEE 2015)
Sample Questions
Ques 1. The term modulation in a computer network refers to what? (1 mark)
Ans. Modulation is an additional means of encoding information into a carrier. With the aid of a computer network, communication is done by periodic waveforms decoded into readable information.
Ques 2. Which modulation technique is best? (2 marks)
Ans. Those whose modulations depend on amplitude have a greater likelihood of distortion due to noise. By contrast, modulations based on phase and frequency eliminate distortion and demand less power for clearer transmissions.
Ques 3. How do you describe a baseband signal? (2 marks)
Ans. The baseband signal refers to an unmodulated transmission that has not been demodulated or modulated back to its original frequency. Coaxial cables and optical fibres are two ways in which information can be transmitted.
Ques 4. Is Modulation Necessary? (2 marks)
Ans. Based on our findings, direct transmission of baseband signals is not compatible with direct transmission of data. When modulating with a high-frequency carrier wave, the strength of such a signal can be made much larger and extend over much longer distances without impacting its modulating parameters.
Ques 5. Why do we need higher bandwidth for the transmission of music compared to that for commercial telephonic communication? (CBSE 2009) (1 mark)
Ans. The range of frequencies of music is higher than commercial telephone conversation and therefore, greater bandwidth is needed for music. Also, it is free from noise.
Ques 6. Identify the parts X and Y in the following block diagram of a generalised communication system. (CBSE 2009) (2 marks)
Ans. According to the question in the figure,
- X: Information source.
- Y: Communication channel
Ques 7. Define the term modulation. Draw a block diagram of a simple modulator for obtaining AM signals. (CBSE 2009) (2 marks)
Ans. Modulation is the process in which low-frequency message signals are superimposed on high-frequency carrier waves so that they can be transmitted over long distances. The block diagram for a simple modulator for obtaining AM signal is shown below:
Ques 8. Figure shows a block diagram of a transmitter. Identify the boxes X and Y and write their functions. (CBSE 2012) (2 marks)
Ans. 
- X is Modulator Since the frequency range of the signal is quite low and it is associated with a very small amount of energy. It dies out very soon if transmitted as such. So, it is modulated by mixing with very high-frequency waves called carrier waves. This is done by modulator power.
- Y is Amplifier Since, the signal gets weaker after travelling through long distances it cannot be transmitted as such. Thus, we use a power amplifier to provide it necessary power before feeding the signal to the transmitting antenna
Ques 9. Write two factors justifying the need for modulation for the transmission of a signal. (CBSE 2009) (3 marks)
Ans. The needs of modulation for the transmission of a signal are given as below:
(i) The transmission of a low-frequency signal needs an antenna of 4-5 km which is impossible to construct. So, there is a need to modulate waves in order to reduce the height of the antenna to a reasonable height.
(ii) The effective power seen to radiate by the antenna for low wavelength or high frequency can be expressed as, \(P \propto {{1} \over \lambda^2}\). Hence, modulating the wave is required for effective radiation.
Ques 10. Distinguish between amplitude modulation and frequency modulation. (CBSE 2012) (1 mark)
Ans. The amplitude modulation provides a larger coverage area, while frequency modulation provides a better quality transmission.
Ques 11. Write two factors that justify the need of modulating a low-frequency signal into high frequencies before transmission. (CBSE 2012) (2 marks)
Ans. Need of modulating a low-frequency signal :
(i) The size of the antenna or \((L \sim {{\lambda} \over 4})\)
(ii)Transmission of audio frequency electrical signals needs a long impracticable antenna.
(iii) To avoid mixing-up of signals from different transmitters.
Ques 12. Define modulation index. Why is it generally kept less than one? (CBSE 2017) (2 marks)
Ans. Modulation index is defined as the ratio of the amplitude of modulating signal (Am) to the amplitude of carrier wave (Ac)
\((\mu) = \frac {A_m} {A_c}\)
It is kept less than one to avoid distortion.
Ques 13. What is analog modulation and its various techniques? (3 marks)
Ans. In analog modulation, the modulating technique is applied to the analog information signal. The various techniques of analog modulation are:
- Amplitude modulation(AM)
- Frequency modulation(FM)
- Phase modulation(PM)
Ques 14. What is the difference between coherent and non-coherent demodulation? (2 marks)
Ans. In the case of coherent, the carrier used for demodulation is in phase and frequency synchronism with the carrier used for modulation purposes while for non-coherent demodulation, it is not in synchronism.
Ques 15. What is the depth of modulation? (2 marks)
Ans. Depth Modulation refers to the ratio of the unmodulated carrier amplitude to the amplitude deviation for which the modulated carrier wave reaches its minimum value.
Ques 16. What’s the difference between the detector and a demodulator? (2 marks)
Ans. A detector recovers information of interest that is contained in a modulated wave.
Demodulation is an updated form of detector extracting the original information from a modulated carrier wave.
Ques 17. What are the techniques of demodulation? (3 marks)
Ans. The different techniques of demodulation are –
- For a signal modulated with a linear modulation such as AM, a synchronous detector can be used.
- For a signal modulated with an angular modulation, an FM demodulator or a PM demodulator can be used.
Ques 18. What is modulation and demodulation? (2 marks)
Ans. Modulation alters the characteristics of amplitude, frequency, or phase angle of a high-frequency signal according to the instantaneous value of the modulating wave.
Demodulation is the process of extracting original information signal from a modulated carrier signal.
Ques 19. Why frequency modulation is better than amplitude modulation? (1 mark)
Ans. Modulation is better than amplitude modulation as it provides more resistance to noise as compared to demodulation.
Ques 20. Which type of modulation is used in TV transmission? (1 mark)
Ans. Vegestial side band modulation (VSBM) is used for TV transmission.
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