Frequency modulation 3 represent the sidebands of the carrier. Pivot chord modulation the most common type of modulation is called a pivot chord modulation. All the transmitted power in fm is useful, while in am most of the power in carrier and useless. Frequency modulation keeps constant the amplitude of the highfrequency oscillation that is used as a signal and to vary the instantaneous frequency for presenting the information. Consequently, unlike amplitude modulation, the spectrum of an fm signal is. Upon completion of the experiment, the student will. In digital modulation, the modulation technique used is pulse code modulation pcm where the analog signal is converted into digital form of 1s and 0s. Frequency modulation fm is a technique in which the frequency of a transmitted waveform is varied according to the variations in the message wave.
Pdf theoretical description of frequency modulation and. Narrowband fm involves a limited modulating bandwidth and allows for easier analysis. In radio transmission, an advantage of frequency modulation is that it. Narrowband frequency modulation narrowband fm means that the fm modulated wave has narrow bandwidth. Pm and digital modulation s p where 2 is the pkpk phase change in one symbol duration, t for digital signals the modulation index. Chapter 8 frequency modulationfm fm was invented and commercialized after am. The exciter section contains the carrier oscillator, reactance modulator and the buffer amplifier the frequency multiplier section, which features several frequency multipliers the power output section, which includes a low. This choice of key determines the scale you use, how many sharps and flats there are and what chords you can use. Radio theory the basics l differences between very high frequency vhf and ultra high frequency uhf. Amplitude modulation a1 49 you will see in this experiment, and in others to follow, that there is no problem in generating an am signal with a depth of modulation exceeding 100%, and without any rf distortion whatsoever. The main reason behind using the fm modulations by the radio stations is the quality of the signal that can.
Fm system is more immune to noise so higher signal to noise ration sn due to guard band interference from adjacent channel does not take place. Or the process of modulation can be defined as varying the rf carrier wave in accordance with the intelligence or information in a low frequency signal. But we are getting ahead of ourselves, as we have not yet even defined what am is. The simplest method for representing this kind of modulation is fresnels vectorial representation with a consideration of the phase. Introduction manner in which it differs from amplitude modulation, and details associated with f m receiver servicing problems. Amplitude modulation produces an output signal the bandwidth of. Types of modulation 6 flynnkatz 7810 analog modulation amplitude modulation, am frequency modulation, fm double and single sideband, dsb and ssb digital modulation phase shift keying. Modulation is the process of converting data into electrical signals optimized for transmission. When the audio signal is modulated onto the radio frequency carrier, the new radio frequency signal moves up and down in frequency. The exciter section contains the carrier oscillator, reactance modulator and the buffer amplifier. As a result, most data transmission system use psk and qam.
This is further developed as delta modulation dm, which will be discussed in subsequent chapters. Berrou c, glavieux a, thitimajshima p 2010 near shannon limit errorcorrecting pdf. Fm transmitter fm transmitter block diagram direct method. It was the earliest modulation technique used to transmit voice by radio. Phase modulation is similar to frequency modulation and is an important technique in digital communication systems. Demodulation is defined as the process of extracting this information. Discuss the requirements for recovery of intelligence from an am signal and describe the theory of operation of the following am demodulators. Or modulation is defined as the precess by which some characteristics, usually amplitude, frequency or phase. This type of modulation technique is used in electronic communication. Amplitude modulation was developed in the beginning of the 20th century.
In this paper, we will discuss fm theory, fm stereo multiplexing and the rds mechanism. Frequency modulation fm is a process in which the carrier frequency is varied by the amplitude of the modulating signal i. Modulation is defined as the process of transmission of information such as images or videos on an electrical signal. In radio communications, singlesideband modulation ssb or singlesideband suppressedcarrier modulation ssbsc is a type of modulation used to transmit information, such as an audio signal, by radio waves. Frequency modulation fm was invented and commercialized after amplitude modulation. This modulation method is, therefore, referred to as fm or frequency modulation. Fm signals have the same peak frequency deviation, then when mt is a sinusoidal signal set such that the pm and note. In addition to commercial radio, it is used as a component of television signals, for satellite and microwave communications, and for digital data transmission. The idea is simple, though the notion that it can be used to modulate signals for transmission was hardly obvious before its discovery. The article will help especially the student to understand theory of fm modulation and related fm concepts in a much better way. Frequency modulation is that from of angle modulation in which the. The fmmodulated signal has its instantaneous frequency that varies linearly with the amplitude of the message signal. Frequency modulation the fm signal st defined by equation 2. As the resultant is a coded pulse train, this is called as pcm.
The continuous analog signal st is a baseband signal with the information content. It is possible to obtain frequency modulation from phase modulation by the socalled armstrong system. But phase modulation seems to be in a different categorypm radio is by no means a common term. Jul 30, 2019 amplitude modulation am frequency modulation fm phase modulation pm amplitude modulation. A refinement of amplitude modulation, it uses transmitter power and bandwidth more efficiently. Analog modulation is typically used for am, fm radio, and shortwave broadcasting. Essentially an amplitude modulated wave consists of a radio frequency carrier a sine wave at one frequency, typically in the radio frequency portion of the spectrum. This is accomplished through modulation of radio signals. It is interesting, then, to find that am and narrowband fm produce similar changes in the frequency domain.
However if st is sinusoidal, then the instantaneous frequency deviation of the anglemodulated signal is. One modulation technique that lends itself well to digital processes is called iq modulation, where i is the inphase component of the waveform, and q represents the quadrature component. It can be achieved in a number of ways, but the simplest. Frequency modulation frequency modulation is realized by varying signal frequency in accordance with the modulating signal or message, as in figure 1. The fm is a very popular technique since they are widely used by the fm radio stations. Fm modulation system fm transmitter, reactance modulator. Modulation is the process of encoding information onto a carrier signal which has frequency fc. In theory, an fm signal contains an infinite number of side frequencies so that the. The higher the fre quency of the audio voltage used to modulate the carrier, the greater is the extent of the is that of of com a to. Modulation techniques are roughly divided into four types. Theory of frequency modulation and phase modulation.
In theory an fm signal contains an infinite number of side frequencies so that the band. Am and fm timedomain waveforms for the same baseband and carrier signals look very different. The application of the heterodyne principle to modulation is shown schematically in figure 143. Frequency modulation fm is that form of angle modulation in which the. Angle modulation changes the phase of a signal as well as its amplitude, where amplitude modulation leaves the phase unchanged. Although it is important to note that a modulation has occurred, it is even more crucial to understand how the effective modulation took place. Modulation is the process of superimposing a low frequency signal on a high frequency carrier signal. Amplitude modulation is an increase or decrease of the carrier voltage ec, will all other factors remaining constant. It is also used in telemetry, radar, seismic prospecting, and monitoring newborns for seizures via eeg, twoway radio systems, music synthesis, magnetic taperecording systems and some videotransmission systems. Balanced zerocrossing fm detector this is a hybrid circuit analog and digital combination if fi fc.
Fm transmitter is the whole unit which takes the audio signal as an input and delivers fm modulated waves to the antenna as an output to be transmitted. Frequency modulation frequency modulation is a change in the carrier frequency fc with all other factors remaining constant. L difference between amplitude modulation am and frequency modulation fm. L the purpose of a repeater and when it would be necessary. Pdf we present a comprehensive theory for heterodyne absorption spectroscopy with phasemodulated light. Frequency modulation fm is a form of modulation in which changes in the carrier wave frequency correspond directly to changes in the baseband signal. Frequency modulation 1 objective to understand the principles of frequency modulation and demodulation.
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. What is fm, frequency modulation electronics notes. Frequency modulation fm frequency modulation is that from of angle modulation in which the instantaneous frequency fi t is varied linearly with the message signal mt. It is known as the deviation and is normally quoted as the number of kilohertz deviation. In its various forms, iq modulation is an efficient way to transfer information, and it also works well with digital formats. Describe fm demodulation circuit operation for the phaseshift and gatedbeam discriminators and the ratiodetector demodulator. Is a nonlinear function of the modulating signal mt, which makes frequency modulation a nonlinear modulation process. Modulation fm, amplitude shift keying ask, phase shift keying psk, etc. Fm modulation and demodulation will be presented and you will implement two types of demodulators, the frequency. Analog iq modulationtransceiver iq signals take on a continuous range of values as viewed in the time domain used for amfm radios, television nonhdtv, and the first cell phones newer systems typically employ digital modulation instead receiver output 2cos2. This carrier signal is called the modulated signal, while the information carrying, or baseband signal is referred to as the modulating signal.
Thus, pm and fm are closely allied, and this is the first reason for considering pm here. The fm demodulation in v93000 will also be briefly introduced. Frequency modulation fm it is a process in which the frequency of the carrier is varied in accordance with the instantaneous value of modulating voltage. Amplitude modulation am frequency modulation fm phase modulation pm amplitude modulation. Its main advantage is that it is more resistant to additive noise than am. Some phase modulation and quadrature amplitude modulation formats have a higher spectral efficiency for data transmission than frequency shift keying, a form of frequency modulation. Principles of communication fm radio tutorialspoint. Fm is considered an analog form of modulation because the baseband signal is typically an analog waveform without discrete, digital values. The basic theory and equations behind amplitude modulation are relatively straightforward and can be handled using straightforward trigonometric calculations and manipulation. Principles of communication modulation tutorialspoint. Phase modulation is another type of angle modulation very similar to frequency modulation. Frequency modulation is widely used for fm radio broadcasting. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. It help to understand how the fm radio stations transmit the voice signals.
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 amount by which the signal moves up and down is important. All about modulation part i basic concepts, signal space, constellations and phase shift keying modulations psk, qpsk, oqpsk, mpsk. Oct 12, 2018 angle modulation may be subdivided into two distinct types. Fm concepts explained what is frequency modulation. Amplitude modulation, am, is one of the most straightforward ways of modulating a radio signal or carrier. Fm has poorer spectral efficiency than some other modulation formats.
Phase modulation phase modulation is a change in the carrier phase angle. The first practical system was put forward in 1936 as an alternative to am in an effort to make. Its amplitude a, which leads us to the class of systems designated as amplitude. It is possible to look at the theory of the generation of an amplitude modulated signal in four steps.
An fm spectrum is influenced by the modulation index as well as by the ratio of the amplitude of the modulating signal to the frequency of the modulating signal. The amount of change in frequency is determined by the amplitude of the modulating signal. In both cases a lowfrequency spectrum including the. Instantaneous frequency the instantaneousfrequencyof cos. Fm concepts before we start discussing fm modulation we take a look at some important. Narrowband frequency modulation results in a translation of the spectrum of the integral of the baseband signal to a band surrounding the carrier frequency. Analog modulation, digital modulation, pulse modulation, and spread spectrum method. Mar 05, 2019 frequency modulation fm is a form of modulation in which changes in the carrier wave frequency correspond directly to changes in the baseband signal. Since the frequency change of a sinusoid in time results in alternation of phase in time, fm may also be referred to as phase modulation, or pm, as well.
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