A message carrying signal is the one that has to get transmitted over a certain distance, and for it to establish a reliable communication, it requires the help of a high-frequency signal, which should not affect the original properties or characteristics of the transmitted message signal.
If the characteristics of the message signal are changed, then the message contained in it also alters. Therefore, it is essential to take care of the transmitted message signal. A high-frequency signal can travel up to a larger distance, that too, without getting affected by external disturbances. We usually take the help of such a high-frequency signal called a carrier signal for transmitting the message signal. The process is known as Modulation.
Modulation refers to the process of changing the parameters of the carrier signal corresponding to the instantaneous values of the modulating signal.
What is a Baseband Signal?
A baseband signal refers to a transmission signal that hasn’t been modulated or demodulated to its original frequency. It can be transmitted over optical fibres, coaxial cables.
What is the Need for Modulation?
The baseband signals are not compatible with direct transmission. For such a signal to travel much larger and longer distances, its strength has to be increased by modulating with a high-frequency carrier wave, which doesn't affect the parameters of the modulating signal.
Advantages of Modulation
Before the concept of modulation, the antenna used for transmission had to be large enough. Consequently, the range of communication used to get limited as the wave couldn't travel to a distance without getting distorted.
The advantages of implementing modulation in the communication systems are as follows:
The size of the antenna gets reduced
There’s no scope for signal mixing
The communication range increases
Multiplexing of signals occurs
Adjustments in the bandwidth are allowed
Improvement in the reception quality
What are the Different Types of Modulation?
There are several different types of modulations. Based on the modulation techniques used, they are categorized into the types, as shown in the following figure.
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Modulation is broadly classified into continuous-wave modulation and pulse modulation.
In the continuous-wave modulation, a high-frequency sine wave is used as a carrier wave, whereas, in Pulse modulation, a periodic sequence of rectangular pulses is used as a carrier wave.
Amplitude Modulation
If the amplitude of the high-frequency carrier wave is varied following the instantaneous amplitude of the modulating signal, it is known as Amplitude Modulation.
If the angle of the carrier wave is varied, following the instantaneous value of the modulating signal, it is known as Angle Modulation.
The angle modulation is further classified into frequency and phase modulation.
Frequency Modulation
If the frequency of the carrier wave is varied, following the instantaneous value of the modulating signal, it is known as Frequency Modulation.
Phase Modulation
If the phase of the high-frequency carrier wave is varied following the instantaneous value of the modulating signal, it is known as Phase Modulation.
Difference Between Modulation and Demodulation
Modulation is defined as the process of mixing a signal with a sinusoid to produce a new signal. The new signal has quite a few benefits over an un-modulated signal. To be specific, the mixing of the low-frequency signal with the high-frequency carrier signal is known as modulation.
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The term Demodulation refers to the process of extracting the original information-bearing transmitted signal from a carrier wave. A demodulator is an electronic circuit, which is used to recover the information content from the modulated carrier wave.
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FAQs on Modulation and Demodulation
1. What are modulation and demodulation in a communication system?
Modulation is the process of superimposing a low-frequency information signal (like voice or data), also known as the message signal, onto a high-frequency wave called the carrier wave. This is done at the transmitter. Demodulation is the reverse process, performed at the receiver, where the original message signal is extracted from the carrier wave. Essentially, modulation prepares a signal for long-distance travel, and demodulation retrieves it at the destination.
2. Why is modulation a necessary step in long-distance communication?
Modulation is crucial for several practical reasons:
- Reduces Antenna Size: The height of an antenna required for efficient transmission is related to the wavelength of the signal. Low-frequency message signals have very long wavelengths, requiring impractically large antennas. By modulating them onto a high-frequency carrier, the wavelength is reduced, allowing for practical, smaller antennas.
- Prevents Signal Mixing: If multiple stations transmitted their original low-frequency signals simultaneously, they would all mix and interfere with each other. Modulation allows each station to use a different carrier frequency, enabling a receiver to tune into a specific one without interference.
- Increases Transmission Range: High-frequency signals can travel longer distances with less power loss (attenuation) compared to low-frequency signals.
3. What are the main types of analog modulation?
There are three primary types of analog modulation, where a property of the carrier wave is varied in accordance with the message signal:
- Amplitude Modulation (AM): The amplitude of the high-frequency carrier wave is changed 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.
4. What is the fundamental difference between AM and FM radio broadcasts?
The main difference lies in how information is encoded and its resulting quality. In AM (Amplitude Modulation), sound information is carried by changes in the signal's amplitude. In FM (Frequency Modulation), it's carried by changes in the signal's frequency. Because most natural and man-made electronic noise creates amplitude spikes, AM signals are highly susceptible to interference, resulting in static. FM signals, being constant in amplitude, are largely immune to this noise, which is why FM broadcasts typically have much higher sound fidelity and clarity.
5. What does the 'modulation index' signify in Amplitude Modulation?
The modulation index (μ) in AM is a measure of how much the carrier wave's amplitude is varied by the message signal. It is defined as the ratio of the amplitude of the message signal to the amplitude of the carrier wave. Its value is critical for signal quality:
- If μ < 1 (Undermodulation), the signal is transmitted successfully but may be weak.
- If μ = 1, it is considered perfect modulation.
- If μ > 1 (Overmodulation), the carrier wave's amplitude is reduced to zero for an extended period, leading to severe distortion and loss of information in the received signal.
6. Can you provide a simple real-world example of modulation and demodulation in action?
A perfect example is a commercial radio station. When a radio jockey speaks into a microphone, their voice (a low-frequency message signal) is taken and used to modulate a unique, high-frequency carrier wave assigned to that station (e.g., 98.3 MHz). This modulated wave is then broadcast. Your car radio (the receiver) tunes into 98.3 MHz, picks up this wave, and performs demodulation to extract the jockey's original voice signal, which is then amplified and played through your car speakers.
7. How does digital modulation differ from the analog modulation used in AM/FM radio?
The key difference is the nature of the information signal. In analog modulation (like AM/FM), a continuous signal (like a sound wave) varies the carrier wave. In digital modulation, the information is not continuous but is in the form of discrete bits (1s and 0s). The carrier wave's characteristics (amplitude, frequency, or phase) are switched between a fixed number of pre-set values to represent these bits. Common examples include Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), and Phase Shift Keying (PSK), which form the basis of most modern wireless data communication like Wi-Fi and Bluetooth.
