Frequency modulation can be changed to phase modulation by simply adding a cr network to the modulating signal that integrates the modulating signal. Hapter modulation and demodulation mit opencourseware. Therefore we only consider the case where the message signal mtis a sinusoidal signal. Phase modulation is one of the two principal forms of angle modulation, together with frequency modulation. The sound quality offered by am radio stations is poorer, having low. The output is a passband representation of the modulated signal. Difference between amplitude modulation and frequency modulation type of modulation. Carrier phase ft modulates ct in either amplitude, frequency or phase. Phase modulation weichih wang southern taiwan university of technology. For example, the signal in a cell phone is a voice signal with a bandwidth of about 4 khz. Phase modulation is one of the two principal forms of angle modulation, together with frequency modulation the phase of a carrier signal is modulated to follow the changing signal.
Amplitude modulation am frequency modulation fm phase modulation pm click on the links given above to know more. Pm have much in common and they are usually concluded as angle modulation, i. Phase modulation amplitude modulation frequency modulation may be any one of the above. The output signals frequency varies with the input signals amplitude. Frequency modulation is that from of angle modulation in which the instantaneous. Digital phase modulation and demodulation request pdf. In frequency modulation fm, unlike am, the amplitude of the carrier is kept constant, but its frequency is altered in accordance with variations in the audio signal being sent. Introduction manner in which it differs from amplitude modulation, and details associated with f m receiver servicing problems. Phase modulation pm is another form of angle modulation.
The classic definition of fm is that the instantaneous output frequency of a transmitter is varied in accordance with the modulating signal. The similarity between phase modulation and frequency modulation becomes clear if we consider a single frequency baseband signal. Recall that we can write an equation for a sine wave as follows. This page on amplitude modulation am vs frequency modulation fm vs phase modulation pm describes difference between amplitude modulation, frequency modulation and phase modulation types all these modulation types are analog modulation techniques. All about modulation part i basic concepts, signal space, constellations and phase shift keying modulations psk, qpsk, oqpsk, mpsk. The process of phase modulation is quite east than frequency modulation.
Phase modulation machzehnder interferometer with a phase modulator in one arm optical fibre version of the same interferometer 9. In figure 219, note that the unmodulated carrier has constant phase, amplitude, and frequency. Digital phase modulation can either be linear or nonlinear. One approach to reduce this interference, known as.
Oct 09, 2014 frequency modulation and application submitted by. In fm, the information of a signal is encoded in its frequency. In words, the angle is used to carry information in a. Because for this the carrier is required to be constant and this is obtained in case of phase modulation.
It encodes a message signal as variations in the instantaneous phase of a carrier wave. Pdf optical single sideband signal generation using. Phase modulation equation of phase modulation pm wave. Frequency modulation frequency modulation is a type of modulation where the.
The frequency of a radiofrequency channel can be explained best as the frequency of a carrier wave. The height of each vertical line is drawn in proportion to its. Modulationtypesamplitude,frequency,phase modulation. If the input is u t as a function of time t, then the output is. An important feature of angle modulation is that it can provide better. Fm signals have the same peak frequency deviation, then when mt is a sinusoidal signal set such that the pm and note. Explain the advantages and disadvantages of the different analog modulation techniques. Phase modulation pm is used primarily in digital communication. Lecture 2829 fm frequency modulation pm phase modulation.
Pdf on jan 1, 2010, geng peng and others published modulation index estimation of frequency and phase modulated signals find, read. Angle modulation is the process in which the frequency or the phase of the carrier varies according to the message signal. Frequency modulation is the process in which the frequency of the carrier signal is varied by the modulating signal while the amplitude remains constant. Frequency modulation simple english wikipedia, the free. Frequency modulation and phase modulation is a system in which the amplitude of the modulated carrier is kept constant, while its frequency and rate of change are varied by the modulating signal.
The signals that represent useful information are difficult to transmitpropagate. In amplitude modulation, the amplitude of the carrier wave is modified in order to transmit information. However if st is sinusoidal, then the instantaneous frequency deviation of the anglemodulated signal is. This is further divided into analog and digital modulation. Power content of frequency modulation and phase modulation. Here, we consider two representative schemes, namely, phase modulation and frequency modulation. Amamplitude modulation fm frequency modulation pm phase modulation in phase modulation, modulation index is directly proportional to modulating voltage only while in frequency modulation, modulation index is also inversely proportional to modulat. The carrier amplitude is constant and the phase variation of the signal contains the information.
Television broadcasting is done with amplitude modulation for video signals and frequency modulation for audio signals. The subject of frequency modulation involves some con tradictions of existing practices and in general introduces new thoughts in connection with the operation of radio communication systems, transmitters and receivers alike. Phase modulation pm is a modulation pattern for conditioning communication signals for transmission. Digital phase modulation and demodulationdigital phase.
During the process of frequency modulation, the peaks of each successive cycle in the modulated waveform occur at times other than they would if the carrier were unmodulated. Both the input and output signals are real scalar signals. There are two common forms of angle modulation, namely, phase modulation and frequency modulation. The similarity between phase modulation and frequency modulation becomes clear if we consider a singlefrequency baseband signal. The big advantage of frequency modulation is its noise reduction ability, because most of noise is appeared as additional amplitude and in fm the amplitude of signal is hold fixed. Based on the above awgn model, then for an observation of k data intervals, the conditional probability of the received signal given the data and the modulation. Index for some common functions using frequency and phase modulation abstract the equations defining the amplitude of sidebands resulting from either frequency modulation or phase modulation by either squarewave, sinewave, sawtooth or triangular modulating functions are presented. Difference between amplitude modulation and frequency. Calculate modulation index, signal bandwidth, sideband frequencies and. A carrier wave is purely made up of constant frequency, slightly similar to a sine wave. In frequency modulation, the instantaneous frequency of the carrier wave is modified in order to transmit information.
What is the difference between phase modulation and. In phase modulation the phase of the carrier is caused to shift at the rate of the af modulating signal. In india, radio broadcasting is done through amplitude modulation. Pulse position modulation ppm is an analog modulation scheme in which, the amplitude and the width of the pulses are kept constant, while the position of each pulse, with reference to the position of a reference pulse varies according to the instantaneous sampled value of the message signal.
In an fm wave, the total phase changes due to the change in the frequency of the carrier corresponding to the changes in the modulating amplitude. Request pdf digital phase modulation and demodulation digital phase modulation is a class of power and bandwidthefficient modulations widely used in. Frequency modulation objectives upon completion of this chapter, the student should be able to. In effect, modulation converts ft to a bandpass form, in the neighborhood of the center frequency f c. Bragg grating eliminates the dispersioninduced penalty over. From 2, the instantaneous frequency is obtained as f it f c. If the phase of the high frequency carrier wave is varied in accordance with the instantaneous value of the modulating signal, then such a technique is called as phase modulation. What is the difference between phase modulation and frequency. In telecommunications and signal processing, frequency modulation transmits information over a carrier wave by varying the frequency. Frequency modulation fm was invented and commercialized after amplitude modulation. Theory of frequency modulation and phase modulation.
In telecommunications and signal processing, frequency modulation fm is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave in analog frequency modulation, such as fm radio broadcasting of an audio signal representing voice or music, the instantaneous frequency deviation, the difference between the frequency of the carrier and its center. All communications toolbox demodulator functions, system objects and blocks can demodulate binary data using either hard decisions or soft decisions. It is in the field of telecommunications and signal processing, that this kind of technique is mostly used. Interference when two or more optical waves are present simultaneously in the same region of space, the total wave function is the sum of the individual wave functions. We therefore assume mta mcos2 f mtfor pm and mta msim2 f mtfor fm. Am broadcast signals are mainly propagated by ground waves during the day and by sky waves at. Optical single sideband signal generation using phase modulation of semiconductor optical amplifier. Yet people tend to point out that what this synth implemented was in fact not fm synthesis, but pm phase modulation synthesis.
Amplitudeshift keying ask frequencyshift keying fsk phaseshift keying psk all of these techniques vary a parameter of a sinusoid to represent the information which we wish to send. In pulse modulation, a periodic sequence of rectangular pulses, is used as a carrier wave. There are many di erent ways one can put information in it. Jan 18, 2017 i think the spelling need to be checked,as ppt hasnt a meaning, anyhow, modulation means to include a certain message from any type into another transmitted carrier signal, including it has three types,am,fm, and pm pm is phase modulation wh. This demonstration illustrates frequency modulation fm and phase modulation pm using one sinusoidal tone as the modulating signal for fm and pm the modulating signals are defined by and respectively where is the signal frequency in hz and is its amplitude this definition for is used to simplify the spectra of the modulated carrier by using. Phase modulation will also produce an infinite number of sideband frequencies. This is further divided into frequency and phase modulation. Because phase and frequency are related to each other, a generic digital phase modulation may also be viewed as a digital frequency modulation scheme. For example, the signal in a cell phone is a voice signal with a. Modulation index estimation 47 1t is the data symbol rate. Analog communication pulse modulation tutorialspoint.
Look at the signal generator manual to see how to get an fm signal. We shall focus more on frequency modulation in this course and less on phase modulation. Amamplitude modulation fmfrequency modulation pmphase modulation in phase modulation, modulation index is directly proportional to modulating voltage only while in frequency modulation, modulation index is also inversely proportional to modulat. Fm synthesis short for frequency modulation synthesis became all the rage with the release of the dx7 synthesizer. We begin our discussion of digital modulation by starting with the three basic types of digital modulation techniques. Phase and frequency are inseparably linked as phase is the integral of frequency. Pdf optical single sideband signal generation using phase. The frequency components present in the am wave are represented by vertical lines approximately located along the frequency axis. Discuss the differences between am and angle modulation. I always had difficulties in understanding frequency modulation fm and its frequency spectrum. Notice that the phase on the second peak leads the phase of the unmodulated carrier. Frequency modulation is the process of varying the frequency of the carrier signal linearly with the message signal. The concepts of amplitude modulation, modulation and demodulation, along with their. Pdf modulation index estimation of frequency and phase.
Fm frequency modulation pm phase modulation continued ee44510 22 narrowband fm only the j o and j 1 terms are significant same bandwidth as am using eulers identity, and. Frequency modulation requires the oscillator frequency to deviate both above and below the carrier frequency. The dotted wave shape represents the modulated carrier. A phase modulated signal is more immune to noise effects. This form of modulation was developed by the american electrical engineer edwin h. This kind of modulation is used in broadcasting and other radio work in the context of broadcasting, frequency modulation is. Fm is in contrast with amplitude modulation where amplitude of the carrier waves is modulated with frequency remaining. Similarly for pm, the information is encoded in its phase. In telecommunications and signal processing, frequency modulation fm is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave in analog frequency modulation, such as fm radio broadcasting of an audio signal representing voice or music, the instantaneous frequency deviation, the difference between the frequency of the. In other words when phase modulation is applied to a signal there are frequency changes and vice versa. Pm and digital modulation s p where 2 is the pkpk phase change in one symbol duration, t for digital signals the modulation index. However, one factor is very different in phase modulation. Frequency modulation fm is the encoding of the information in a carrier wave by varying the instantaneous frequency of the wave.
The instantaneous frequency of the anglemodulated signal st. Phase modulation pm is that form of angle modulation in which. I think the spelling need to be checked,as ppt hasnt a meaning, anyhow, modulation means to include a certain message from any type into another transmitted carrier signal, including it has three types,am,fm, and pm pm is phase modulation wh. This technique is used to determine the speed of the mobile target. The pm modulator passband block modulates using phase modulation.