Simon and jon hamkins of the many possible modes available for communicating information over a coherent communication channel, one that is quite common is to allocate a portion of the total transmitted power p t to a discrete carrier for purposes of carrier synchronization. Introduction 3 properties of an analog signal can be modulated by information signal. This increasing bandwidth as i increases, is shown in fig. Explain the advantages and disadvantages of the different analog modulation techniques. Introduction manner in which it differs from amplitude modulation, and details associated with f m receiver servicing problems. Overmodulation overmodulation is a condition that occurs when an excessive intelligence signal overdrives an am modulator making %m 100% because e i e c modulated carrier amplitude reach value greater than double of unmodulated value it produces a distortion known as sideband splatter, which results on transmission at frequencies outside. Chapter 6modulation techniques shandong university. A typical f c for lowrate telephone line modems is 1800 hz approximate center of 300 3400 band, and for 1200 baud signaling 1200 pulses per. We reiterate and elaborate on those reasons in section 14. 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.
In chapter 3, the fourier transform pair was defined as ft 1 2 f ej td f fte j tdt. Frequency modulation objectives upon completion of this chapter, the student should be able to. However if st is sinusoidal, then the instantaneous frequency deviation of the anglemodulated signal is sinusoidal. It is in the field of telecommunications and signal processing, that this kind of technique is mostly used. This is considered an analog form of modulation, because the baseband signal is typically an analog waveform without discrete, digital values. Angle modulation continuing from chapter 3, we now focus on the tterm angle in the general modulated carrier waveform x c. Modulation is the process of superimposing a low frequency signal on a high frequency carrier signal. Two signals are involved in the modulation process. Frequency modulation fm is the encoding of the information in a carrier wave by varying the instantaneous frequency of the wave.
Since frequency modulation is a nonlinear process, an exact description of the spectrum of an frequencymodulated signal for an arbitrary message signal is more complicated than linear process. In its simplest form, frequency modulation uses two oscillators. Frequency modulation is a powerful method of synthesis that is as relevant to analogue synthesizers as it is to digital ones, and which is capable of generating sounds unobtainable by any other method. Glavieux a, thitimajshima p 2010 near shannon limit errorcorrecting pdf. Using amplitude modulation to shift the baseband signal fm radio 88mhz108 mhz. Modulation index is a measure of the relationship between deviation and the modulating signals frequency. Frequency modulation is the process in which the frequency of the carrier signal is varied by the modulating signal while the amplitude remains constant. Calculate modulation index, signal bandwidth, sideband frequencies and.
These two waves, usually sinusoids, are out of phase with each other by 90 and are thus called quadrature carriers hence the name of the scheme. Although its old technology, it is still widely used in. Modulation concep modulation is the process by which a message or informationbearing signal is transformed into another signal to facilitate transmission over a communication channel requires an auxiliary signal called carrier the modulation process. Frequency modulation frequency modulation is the process by which frequency of the carrier signal ct changes with respect to the modulating signal mt.
This chapter describes the essential principles behind. Online chapter 3 modulations in classical music artist in residence. Chapter 7 spreadspectrum modulation spread spectrum technique simply consumes spectrum in excess of the minimum spectrum necessaryto send the data. We therefore assume mta mcos2 f mtfor pm and mta msim2 f mtfor fm. Modulation has the effect of moving the baseband signal spectrum to be centered frequencies around the frequency of the carrier. As mentioned earlier, the amplitude is kept constant. Contents of manuals for iq modulation generator amiq. Frequency modulation fm is a form of modulation in which changes in the frequency of the carrier wave correspond directly with changes in the baseband signal. 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. Therefore we only consider the case where the message signal mtis a sinusoidal signal. Communication systems has used a very clever technique called modulation to increase the reach of the signals.
Frequency versus amplitude modulation l amplitude modulation am l changes the amplitude of the carrier signal according to the amplitude of the message signal. Fm signals are used in technology such as radars, telemeters, eeg, radio broadcasting, satellite communication and magnetic tape recording systems. Amplitude modulation or just am, which is the main topic of this chapter. By successfully completing the occecc, you indicate that you have met the objectives and have learned.
Frequency modulation, fm, variation of the frequency of a carrier wave in accordance with the characteristics of a signal. We can describe the modulation from d major to a major by saying that the b minor chord in bar 6 acts as a common chord or pivot chord between the. Modulation is the process of encoding information onto a carrier signal which has. Chapter fifteen communication systems not to be republished. Chapter 2 concerns all the general problems of frequency modulation, while chapter 3 deals with the propagation distortion, which is apparent in a variablevelocity guided transmission channel, and, which appears on an echoing path either in free space, or over a badly matched feeder. Its main advantage is that it is more resistant to additive noise than am.
In these applications its particular advantages can be used to good effect. Whilst other forms of modulation are being used in many areas, fm still offers the highest quality for broadcasting and many advantages. Frequency modulation is widely used for radio transmission due to the fact that the signaltonoise ratio snr is large in this method of modulation and hence radio frequency interference is minimized. Chapter 4 frequency modulation linkedin slideshare. The number of times per second that the instantaneous frequency is varied from the average carrier. All about modulation part i basic concepts, signal space, constellations and phase shift keying modulations psk, qpsk, oqpsk, mpsk. The synthesis of complex audio spectra by means of frrequency modulation september 1973, volume 21, number 7 2 yield a negative scaling coefficient for some components. Relevant modulation microsoft office outlook 2007 tutorial pdf free download schemes qpsk, gmsk, mary schemes. In this method of modulation the amplitude of the carrier wave is maintained. Of all the methods of impressing information onto a carrier signal, am is the oldest. Chapter handbook of optics photonics research group.
Next month, well take a closer look at some practical aspects of frequency modulation, and introduce the idea of operators a common. Amplitude modulation is defined as the process in which the amplitude of the carrier wave ct is varied about a mean value, linearly with the 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. Irrespective of its nature, every communication system has three essential. Or modulation is defined as the precess by which some characteristics, usually amplitude, frequency or phase, of a carrier is varied in. Frequency modulation is widely used in many areas of radio technology including broadcasting and areas of two way radio communication. An am wave may thus be dscribed, in the most general form, as a function of time as follows. This results in oscillations similar to those illustrated in view b. Chapter 8 frequency modulationfm fm was invented and commercialized after am. Modulation types of modulation definition applications.
Amplitude modulation chapter 3 objectives at the conclusion of this chapter, the reader will be able to. The synthesis of complex audio spectra by means of. Chapter 4 automatic modulation recognition frequency and phase conventionally, modulation identification is performed by i decision theoretic dt approach ii statistical pattern sp approach iii spectral processing iv instantaneous amplitude, phase and frequency histogram techniques v hybrid scheme. Play the following progression on your guitar or on the keyboard. 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. Discuss the differences between am and angle modulation. This is a modulation scheme which conveys data by changing modulating the amplitude of two carrier waves. Modulation for analog nyu tandon school of engineering. Ee4512 analog and digital communications chapter 6 the dsbsc am coherent receiver has a bandpass filter centered at f c and with a bandwidth of twice the bandwidth of st because of the lsb and usb.
Each radio station is assigned 200 khz, to transmit a stereo audio. We discussed in chapter 10 why it is generally untenable to directly transmit baseband signals over communication links. Frequency modulation while amplitude modulation synthesis changes the gain or volume of an audio signal, frequency modulation synthesis, or fm synthesis, is used to make periodic changes to the frequency of an oscillator. Spectra have a typical trapezoidal shape in linear frequency and amplitude in decibels. Instantaneous frequency the instantaneousfrequencyof cos. The classical marconi radio used a modulation technique known today as. Frequency modulation ni community national instruments. Fm is in contrast with amplitude modulation where amplitude of the carrier waves is modulated with frequency remaining unchanged and constant. An introduction to frequency modulation sound on sound. The left and right channels each limited to 15khz are multiplexed into a single baseband signal using amplitude modulation using frequency modulation to shift the baseband. In frequency modulation, the instantaneous frequency of the radiofrequency wave is varied in accordance with the modulating signal, as shown in view a of figure 25.
The comprehensive check questions are based on the objectives. Introduction angle modulation modulation where the angle of a sinewave carrier is varied as a function of the intelligence amplitude. Generally high carrier frequency is used to modulate the voice signal. We may define the instantaneous frequency of the angle modulated signal st as. Chapter 8 modulation, protocols, and modes wednesday, october 12, 2016 3 modulation index page 84 the ratio of the maximum signal frequency deviation to the instantaneous modulating frequency is called the modulation index. The modulation to the dominant takes place in the dynamic harmony of the closing section where the progression moves the tonality from the tonic d to the cadence in the dominant key of a major. Phase modulation of the carrier with a message signal is equivalent to frequency modulation of the carrier with the derivative of the message signal.
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