Amplitude frequency and phase modulation pdf

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amplitude frequency and phase modulation pdf

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Comparing and Contrasting Amplitude, Frequency, and Phase Modulation

When audio signals are transmitted over thousands of kilometres through radio transmission, the audio frequencies that lie within the frequency range of 15 Hertz to 20 KiloHertz has very small signal power and thus cannot be transmitted via the antenna for communication purposes.

The radiation of electrical energy is only possible at frequencies above 20 KiloHertz. The main advantage of high-frequency signals is that they can be transmitted over very long distances by dissipating very small power.

Thus, the audio signals must be sent along with the high-frequency signals for communication. This can be done by superimposing electrical audio signals on a high-frequency wave called the carrier wave.

The carrier wave is generated from radio-frequency oscillators and is undamped in nature. Thus, when the audio-frequency signal is superimposed on a carrier wave, the resulting wave gets all the characteristics of the audio signal.

The method of superimposing an audio signal over the carrier wave is called modulation. After modulation is done, the resulting wave can be given to the antenna and the signal can be transmitted over a long distance.

The speech or music that is to be broadcasted consists of a series of compressions and rarefactions. A microphone acts as a transducer to convert these parameters into its corresponding varying current measures. With the difference in the measure of sound, the corresponding change in the frequency of the electrical current is also produced, and they lie in the audio-frequency range and therefore, it is known as an audio-frequency signal.

Since the signal strength of this low-frequency signal is less, it has to be given to an audio-frequency amplifier to strengthen the signal to a desired level. These low-frequency signals cannot be sent over long distances by radiating it out directly from the aerial. Thus, the audio frequency signal has to be modulated with a radio-frequency carrier wave.

The carrier wave can be produced using any oscillator. The radio frequency waves have a constant amplitude and travel through space with the velocity of light. This is why you can see and hear live broadcasts with very little delay. The resulting modulated wave is radiated out of the transmitter antenna and travels through space until it reaches the receiver antenna. The receiving aerial consists of a receiver that separates both the carrier signal and audio-frequency signal.

The process of the receiver by which the audio frequency is separated from the carrier signal is called demodulation. The demodulated audio signal is sent to the loudspeakers for the user to hear. If there was no demodulation, the high-frequency currents would have reached the loudspeaker and would have caused signal errors. Radiofrequency current also cannot be heard by humans. This shows why modulation and demodulation are important in a communication system. The process of impressing low-frequency information to be transmitted on to a high-frequency wave, called the carrier wave, by changing the characteristics of either its amplitude, frequency or phase angle is called modulation.

The process of altering the characteristics of the amplitude, frequency, or phase angle of the high-frequency signal in accordance with the instantaneous value of the modulating wave is called modulation.

The main function of the carrier wave is to carry the audio or video signal from the transmitter to the receiver. The wave that is resulted due to superimposition of audio signal and carrier wave is called the modulated wave. The reason why low-frequency signals cannot be transmitted over long distances through space is listed below:. Since the three variables are the amplitude, frequency, and phase angle, the modulation can be done by varying any one of them.

Thus there are three modulation types namely:. In India, radio broadcasting is done through amplitude modulation. Television broadcasting is done with amplitude modulation for video signals and frequency modulation for audio signals. The method of varying amplitude of a high-frequency carrier wave in accordance with the information to be transmitted, keeping the frequency and phase of the carrier wave unchanged is called Amplitude Modulation.

The information is considered as the modulating signal and it is superimposed on the carrier wave by applying both of them to the modulator. The detailed diagram showing the amplitude modulation process is given below. As shown above, the carrier wave has positive and negative half cycles. Both these cycles are varied according to the information to be sent. The carrier then consists of sine waves whose amplitudes follow the amplitude variations of the modulating wave.

The carrier is kept in an envelope formed by the modulating wave. From the figure, you can also see that the amplitude variation of the high-frequency carrier is at the signal frequency and the frequency of the carrier wave is the same as the frequency of the resulting wave. V m — Maximum value of the modulating signal. It must be noted that the phase angle remains constant in this process. Thus it can be ignored.

The instantaneous value of amplitude modulated wave is given by the equation. The above equation represents the sum of three sine waves. Thus, the second and third cosine equations are more close to the carrier frequency. The equation is represented graphically as shown below. The frequency components present in the AM wave are represented by vertical lines approximately located along the frequency axis. The height of each vertical line is drawn in proportion to its amplitude.

Since the angular velocity of the carrier is greater than the angular velocity of the modulating signal, the amplitude of sideband frequencies can never exceed half of the carrier amplitude.

Two side banded frequencies will be produced when a carrier is amplitude modulated by a single frequency. When a modulating signal has more than one frequency, two sideband frequencies are produced by every frequency. The sidebands of frequencies present above the carrier frequency will be the same as the ones presented below. The sideband frequencies present above the carrier frequency is known to be the upper sideband and all those below the carrier frequency belong to the lower sideband.

The USB frequencies represent the some of the individual modulating frequencies and the LSB frequencies represent the difference between the modulating frequency and the carrier frequency. The total bandwidth is represented in terms of the higher modulating frequency and is equal to twice this frequency. The ratio between the amplitude change of carrier wave to the amplitude of the normal carrier wave is called Modulation index.

It can also be defined as the range in which the amplitude of the carrier wave is varied by the modulating signal. Another way of expressing the modulation index is in terms of the maximum and minimum values of the amplitude of the modulated carrier wave. This is shown in the figure below. The value of m determines the strength and the quality of the transmitted signal. In an AM wave, the signal is contained in the variations of the carrier amplitude. The audio signal transmitted will be weak if the carrier wave is only modulated to a very small degree.

But if the value of m exceeds unity, the transmitter output produces erroneous distortion. A modulated wave has more power than had by the carrier wave before modulating.

The total power components in amplitude modulation can be written as:. In some applications, the carrier is simultaneously modulated by several sinusoidal modulating signals.

In such a case, the total modulation index is given as. If Ic and It are the r. Very simple and easy to understand.. A carrier frequency on its own has no information and, if you tune in to this frequency on the receiver, all you will hear is silence. If, on the other hand, the carrier frequency is modulated with information for example, speech or music and your receiver is tuned to the carrier frequency, this signal is demodulated in the receiver and you can hear the information.

Demodulation, as the name implies, is the extraction of what was modulated in the transmitter. I went through the topic Modulation. It was defined very simply and precisely. I appreciate and hope the same thing will keep on going.

Author john. Do you know how RFID wallets work and how to make one yourself? February 14, Jale curuki 6 years ago.

No explanation for FM or PM!!!! Awesome explanation….. CT is always mass!!!!! Louis J. Bruno 8 years ago. What happened to the FM and PM explanation? Safi Khan 9 years ago. Peter 9 years ago. I have gone through this peace and am happy. Joseph Vella-Zarb 9 years ago. Re: Need for Modulation. Submit Type above and press Enter to search. Press Esc to cancel.

Basic Principles of Digital Modulation

How do the different modulation schemes compare in terms of performance and applications? Thus, we need to have a general idea of which modulation scheme is appropriate for a particular application. Amplitude modulation is straightforward in terms of implementation and analysis. Also, AM waveforms are fairly easy to demodulate. Overall, then, AM can be viewed as a simple, low-cost modulation scheme. As usual, though, simplicity and low cost are accompanied by performance compromises—we never expect the easier, cheaper solution to be the best one.

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Comparing and Contrasting Amplitude, Frequency, and Phase Modulation

Amplitude modulation AM is a modulation technique used in electronic communication, most commonly for transmitting messages with a radio carrier wave. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal, such as an audio signal. This technique contrasts with angle modulation , in which either the frequency of the carrier wave is varied as in frequency modulation , or its phase , as in phase modulation.

Prerequisite — Modulation. Frequency Modulation : Frequency Modulation is a modulation in which the frequency of the carrier wave changes according to the instantaneous amplitude of the modulating signal keeping phase and amplitude constant. The frequency of the carrier wave is modified in order to send the data or information. It cannot transmit over long distances, have a smaller range. Its modulation index is always greater than one.

Terahertz THz science and technology promise unique applications in high-speed communications, high-accuracy imaging, and so on. To keep up with the demand for THz systems, THz dynamic devices should feature large phase shift modulation and high speed. To date, however, only a few devices can efficiently manipulate the phase of THz waves. In this paper, we demonstrate that efficient phase modulation of THz waves can be addressed by an active and enhanced resonant metamaterial embedded with a nanostructured 2D electron gas 2DEG layer of a GaN high electron mobility transistor HEMT. The enhanced resonant metaunit couples the traditional dipolar and inductance-capacitance resonances together to realize a coupling mode with enhanced resonance.

When audio signals are transmitted over thousands of kilometres through radio transmission, the audio frequencies that lie within the frequency range of 15 Hertz to 20 KiloHertz has very small signal power and thus cannot be transmitted via the antenna for communication purposes.

Comparing and Contrasting Amplitude, Frequency, and Phase Modulation

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Large phase modulation of THz wave via an enhanced resonant active HEMT metasurface

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COMMENT 1

  • 2. With few exceptions,. Phase Modulation (PM) is used primarily in digital communication. Amplitude, Frequency and Phase Modulation. Drew P. - 05.05.2021 at 06:04

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