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. Pdf theoretical description of frequency modulation and. Balanced zerocrossing fm detector this is a hybrid circuit analog and digital combination if fi fc. Narrowband frequency modulation narrowband fm means that the fm modulated wave has narrow bandwidth. 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 widely used for fm radio broadcasting. Modulation is the process of encoding information onto a carrier signal which has frequency fc. 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. The fm is a very popular technique since they are widely used by the fm radio stations.
All about modulation part i basic concepts, signal space, constellations and phase shift keying modulations psk, qpsk, oqpsk, mpsk. Modulation is the process of converting data into electrical signals optimized for transmission. Narrowband fm involves a limited modulating bandwidth and allows for easier analysis. 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. Fm has poorer spectral efficiency than some other modulation formats. Frequency modulation the fm signal st defined by equation 2. A refinement of amplitude modulation, it uses transmitter power and bandwidth more efficiently. Berrou c, glavieux a, thitimajshima p 2010 near shannon limit errorcorrecting pdf. It can be achieved in a number of ways, but the simplest. Am and fm timedomain waveforms for the same baseband and carrier signals look very different. This type of modulation technique is used in electronic communication.
Its main advantage is that it is more resistant to additive noise than am. Or modulation is defined as the precess by which some characteristics, usually amplitude, frequency or phase. The main reason behind using the fm modulations by the radio stations is the quality of the signal that can. The simplest method for representing this kind of modulation is fresnels vectorial representation with a consideration of the phase. Amplitude modulation was developed in the beginning of the 20th century. Oct 12, 2018 angle modulation may be subdivided into two distinct types. 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. In both cases a lowfrequency spectrum including the. But phase modulation seems to be in a different categorypm radio is by no means a common term. 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. Radio theory the basics l differences between very high frequency vhf and ultra high frequency uhf. As a result, most data transmission system use psk and qam. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam.
In its various forms, iq modulation is an efficient way to transfer information, and it also works well with digital formats. In addition to commercial radio, it is used as a component of television signals, for satellite and microwave communications, and for digital data transmission. Modulation techniques are roughly divided into four types. It was the earliest modulation technique used to transmit voice by radio.
Principles of communication fm radio tutorialspoint. In theory an fm signal contains an infinite number of side frequencies so that the band. Narrowband frequency modulation results in a translation of the spectrum of the integral of the baseband signal to a band surrounding the carrier frequency. 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 frequency modulation is that from of angle modulation in which the instantaneous frequency fi t is varied linearly with the message signal mt. The continuous analog signal st is a baseband signal with the information content. Frequency modulation fm is a process in which the carrier frequency is varied by the amplitude of the modulating signal i. Jul 30, 2019 amplitude modulation am frequency modulation fm phase modulation pm amplitude modulation. Fm concepts explained what is frequency modulation. Thus, pm and fm are closely allied, and this is the first reason for considering pm here. 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. Fm concepts before we start discussing fm modulation we take a look at some important.
Is a nonlinear function of the modulating signal mt, which makes frequency modulation a nonlinear modulation process. However if st is sinusoidal, then the instantaneous frequency deviation of the anglemodulated signal is. 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.
Phase modulation is similar to frequency modulation and is an important technique in digital communication systems. The application of the heterodyne principle to modulation is shown schematically in figure 143. Chapter 8 frequency modulationfm fm was invented and commercialized after am. Demodulation is defined as the process of extracting this information. But we are getting ahead of ourselves, as we have not yet even defined what am is. Amplitude modulation is an increase or decrease of the carrier voltage ec, will all other factors remaining constant. 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. Analog modulation is typically used for am, fm radio, and shortwave broadcasting.
Frequency modulation fm was invented and commercialized after amplitude modulation. L difference between amplitude modulation am and frequency modulation fm. In theory, an fm signal contains an infinite number of side frequencies so that the. This modulation method is, therefore, referred to as fm or frequency modulation. Fm transmitter fm transmitter block diagram direct method. Amplitude modulation produces an output signal the bandwidth of. Fm is considered an analog form of modulation because the baseband signal is typically an analog waveform without discrete, digital values. Although it is important to note that a modulation has occurred, it is even more crucial to understand how the effective modulation took place. In radio transmission, an advantage of frequency modulation is that it. Consequently, unlike amplitude modulation, the spectrum of an fm signal is. The basic theory and equations behind amplitude modulation are relatively straightforward and can be handled using straightforward trigonometric calculations and manipulation. Phase modulation phase modulation is a change in the carrier phase angle. Fm signals have the same peak frequency deviation, then when mt is a sinusoidal signal set such that the pm and note.
Angle modulation changes the phase of a signal as well as its amplitude, where amplitude modulation leaves the phase unchanged. The exciter section contains the carrier oscillator, reactance modulator and the buffer amplifier. In this paper, we will discuss fm theory, fm stereo multiplexing and the rds mechanism. 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. Modulation is the process of superimposing a low frequency signal on a high frequency carrier signal. This is accomplished through modulation of radio signals. Fm modulation system fm transmitter, reactance modulator.
Pdf we present a comprehensive theory for heterodyne absorption spectroscopy with phasemodulated light. It is possible to obtain frequency modulation from phase modulation by the socalled armstrong system. This choice of key determines the scale you use, how many sharps and flats there are and what chords you can use. Modulation fm, amplitude shift keying ask, phase shift keying psk, etc. Frequency modulation 1 objective to understand the principles of frequency modulation and demodulation. Upon completion of the experiment, the student will. Instantaneous frequency the instantaneousfrequencyof cos. Frequency modulation fm is a form of modulation in which changes in the carrier wave frequency correspond directly to changes in the baseband signal. Modulation is defined as the process of transmission of information such as images or videos on an electrical signal. Pm and digital modulation s p where 2 is the pkpk phase change in one symbol duration, t for digital signals the modulation index. 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. 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.
Its amplitude a, which leads us to the class of systems designated as amplitude. Principles of communication modulation tutorialspoint. Frequency modulation 3 represent the sidebands of the carrier. 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. 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. Frequency modulation fm is a technique in which the frequency of a transmitted waveform is varied according to the variations in the message wave. All the transmitted power in fm is useful, while in am most of the power in carrier and useless. 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. Amplitude modulation, am, is one of the most straightforward ways of modulating a radio signal or carrier. Describe fm demodulation circuit operation for the phaseshift and gatedbeam discriminators and the ratiodetector demodulator. Fm modulation and demodulation will be presented and you will implement two types of demodulators, the frequency. Theory of frequency modulation and phase modulation. Pivot chord modulation the most common type of modulation is called a pivot chord modulation.
What is fm, frequency modulation electronics notes. The amount by which the signal moves up and down is important. This is further developed as delta modulation dm, which will be discussed in subsequent chapters. 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. Frequency modulation frequency modulation is a change in the carrier frequency fc with all other factors remaining constant. It is possible to look at the theory of the generation of an amplitude modulated signal in four steps. Discuss the requirements for recovery of intelligence from an am signal and describe the theory of operation of the following am demodulators. 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. Analog modulation, digital modulation, pulse modulation, and spread spectrum method. 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. 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. The fm demodulation in v93000 will also be briefly introduced. This carrier signal is called the modulated signal, while the information carrying, or baseband signal is referred to as the modulating signal.
The goal of this experiment is to become familiar with fm modulation and demodulation. The amount of change in frequency is determined by the amplitude of the modulating signal. It is known as the deviation and is normally quoted as the number of kilohertz deviation. Amplitude modulation am frequency modulation fm phase modulation pm amplitude modulation. Phase modulation is another type of angle modulation very similar to frequency modulation. 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. Introduction manner in which it differs from amplitude modulation, and details associated with f m receiver servicing problems. Looking for a comprehensive article on fm modulation, here it is what you are looking for. Modulation describes the process where a piece of music changes from one key to another key when you start writing a piece of music one of the first things you do is choose a key to compose in. The first practical system was put forward in 1936 as an alternative to am in an effort to make. It is interesting, then, to find that am and narrowband fm produce similar changes in the frequency domain. Let us take a look at the structure of fm transmitter and fm receiver along with their block diagrams and working.
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