Fm synthesis can create both harmonic and inharmonic sounds. Frequency modulation is a form of modulation, which represents information as variations in the instantaneous frequency of a carrier wave. As will be seen, it is the dc component which gives rise to the term. Frequency modulation keeps constant the amplitude of the high frequency oscillation that is used as a signal and to vary the instantaneous frequency for presenting the information. Pdf frequency modulation fm ransariya divyesh academia. Frequency modulation an overview sciencedirect topics. Lab 6 frequency modulation formal report required groups of two this lab will have you create and analyze some simple frequency modulated fm waveforms. Amplitude modulation is defined as a process in which the amplitude of the carrier wave. By increasing or decreasing pulse width, the controller regulates energy flow to the motor shaft. However if st is sinusoidal, then the instantaneous frequency deviation of the anglemodulated signal is. In tims the carrier frequency is generally 100 khz. The two common forms of analog modulation are amplitude modulation am and frequency modulation fm which is speci. Modulation is a technique that changes the characteristics of the carrier frequency in accordance with the input signal. The amount of frequency deviation a signal experiences is a measure of the change in transmitter output frequency from the rest frequency of the transmitter.
Berrou c, glavieux a, thitimajshima p 2010 near shannon limit errorcorrecting pdf. This is generally accomplished using a high frequency carrier sinusoid and a lower frequency modulation waveform such as an audio signal from microphone. Fm the output carrier frequency n x f c the output modulation index n x. If you have the time, take a look at the theory behind phaselocked loops pll, as in pp. Since the amplitude is kept constant, fm modulation is a low noise process and provides a high quality modulation technique which is used for music and speech in hifidelity broadcasts. Pm and digital modulation s p where 2 is the pkpk phase change in one symbol duration, t for digital signals the modulation index. Fm modulation and demodulation will be presented and you will implement two types of demodulators, the frequency. The angle modulation is further divided into frequency and phase modulation. Pdf we present a comprehensive theory for heterodyne absorption spectroscopy with phase modulated light. The foregoing gives, very briefly, the essential reasoning. Frequency modulation fm is the standard technique for highfidelity communications as is evident in the received signals of the fm. Prelab theory a frequency modulation fm waveform can be represented mathematically by.
In analog frequency modulation, such as radio broadcasting, of an audio signal representing voice or music, the instantaneous frequency deviation, i. Design and implementation of test bench for frequency modulation and demodulation by karrar abd alhadi signal and linear system theory 2. Frequency modulation is widely used on frequencies above 30 mhz, and it is particularly well known for its use for vhf fm broadcasting. Pdf narrowband frequency modulation keee343 communication. The general equations presented allow for an arbitrary modulation index and an arbitrary. The frequency modulation is understood as the influencing modulation of the frequency of a carrier by a modulating signal. If the frequency of the carrier wave is varied, in accordance with the instantaneous value of the modulating signal, then such a technique is called as frequency modulation.
Although it may not be quite as straightforward as amplitude modulation, nevertheless frequency modulation, fm, offers. 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. We present a comprehensive theory for heterodyne absorption spectroscopy with phasemodulated light. Modulation fm, amplitude shift keying ask, phase shift keying psk, etc.
The information bearing signal the modulating signal changes the instantaneous frequency of the carrier. This fivechapter text particularly discusses the propagation of the waves used, frequency modulation, and noise and sundry distortions liable to arise either in the course of propagation, in the equipment, and in the methods used for the transmission of the information. Fm is a process in which the carrier frequency is varied by the amplitude of the modulating signal i. Pdf theoretical description of frequency modulation and.
Theory, time domain, frequency domain chapter 4 radio frequency modulation pdf version. Theoretical description of frequency modulation and. An introduction to frequency modulation sound on sound. Designing frequency modulator and demodulator using simulink theory phase modulation pm and frequency modulation fm are special cases of anglemodulated signaling. L difference between amplitude modulation am and frequency modulation fm. This video discusses basics of frequency modulation which includes definition of frequency modulation and also frequency modulated waveform. This experiment deals with the basic performance of frequency modulation. The carrier frequency, fc, should be larger than the highest spectral component.
Frequency deviation may be formally defined as the peak dif ference between the instantaneous frequency of the modulated wave and the carrier frequency. Frequency modulationsimulation experiment introduction. Frequency modulation 1 objective to understand the principles of frequency modulation and demodulation. Frequency modulation definition, applications, advantages. Of course, since n can take any integer value, in theory, applying frequency modulation to a signal produces an infinite series of side bands. Fm signals have the same peak frequency deviation, then when mt is a sinusoidal signal set such that the pm and note. Its amplitude a, which leads us to the class of systems designated as amplitude. The technology is used in telecommunications, radio broadcasting, signal processing, and computing. It is also possible to change the frequency of a signal to give frequency modulation or fm. Angle modulation is the process in which the frequency or the phase of the carrier varies according to the message signal. According to this theory, if 2hwo0 is madeless than p the range of frequencies transmitted 2hao2ir will besmaller thanp2. Application to microwave links covers the theoretical principles of microwave beam technique. Measure and record the frequency of the signal generator with spectrum analyzer. Frequency modulation is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave.
In analog modulation, the characteristics of the modulated sinusoid such as amplitude, frequency or phase can take a continuum of values depending on the source of the information. L the purpose of a repeater and when it would be necessary. An important concept in the understanding of fm is that of frequency deviation. Pdf we present a comprehensive theory for heterodyne absorption spectroscopy with phasemodulated light. In this second experiment, we will examine the most common modulation scheme in daily life, namely, the frequency modulation, or fm. In this video, i have explained frequency modulation fm by following outlines. Phase modulation pm is a different form of frequency modulation and the carrier is similar in appearance to a frequency modulated carrier. In phase modulation pm, the baseband information signal varies the phase of the high frequency carrier. The distortion may be in amplitude, frequency, or phase, depending on the nature of the demodulator. This lab will have you create and analyze some simple frequency modulated fm waveforms. The spectrum of an fm signal is quite complicated and is dependent on mf. Radio theory the basics l differences between very high frequency vhf and ultra high frequency uhf. It needs a carrier signal of higher frequency for long distance destination. We saw in the previous page that frequency modulation is achieved by adding the integral of the baseband signal to the argument of a sine or cosine function where the sine or cosine function represents the carrier.
Modulation is a process of translating information signal from low band frequency to high band frequency that is suits the transmission medium. Angle modulation provides the improved noise performance. The frequency of an oscillator is altered in accordance with the amplitude of a modulating signal. Frequency modulation fm, as well as phase modulation pm, are types of angle exponential modulation. A simple method to achieve fm is to vary the capacitance of a resonant lc circuit in a transmitter. The simplest method for representing this kind of modulation is fresnels vectorial representation with a consideration of the phase. Therefore, by using the characteristic of this structure, we can achieve bfsk modulation easily. We shall focus more on frequency modulation in this course and less on phase modulation. Frequency modulation fm in frequency modulation, the frequency rather than the amplitude of the carrier wave is made to vary in proportion to the varying amplitude of the modulating signal, as shown in fig. What is fm, frequency modulation electronics notes. Theoretical description of frequency modulation and wavelength modulation spectroscopy. Failure to accurately recover this intelligence will result in distortion and degradation of the demodulated signal and intelligence will be lost. Angle modulation changes the phase of a signal as well as its amplitude, where amplitude modulation leaves the phase unchanged. Frequency modulation synthesis or fm synthesis is a form of sound synthesis whereby the frequency of a waveform is changed by modulating its frequency with a modulator.
Principles of communication modulation tutorialspoint. Repeat step 5 by varying frequency of the modulating signal. The technique addresses some of the shortcomings of classic fm and provides a more smoothly evolving spectrum with respect to variations in the modulation. This formalism provides a general description of saturation spectroscopy. We can utilize the ttl signal at pin 9 to control the output frequency to be f1 or f2. Assume that when the input is 5 v, the output frequency is f 1, and when the input is 0 v, the output frequency is f 2. Example commercial fm signals use a peak frequency deviation of. Theory of frequency modulation detection for low acoustical. These are covered in chapter 5 of 2, or chapter 3 of 1. If a carrier center frequency is 100 me and modulation causes the carrier frequency to shift to 100. Frequency modulation definition, basics and waveform hd. Calculate the vco frequency tuning sensitivity hzvolt kv. Frequency modulation is the process of varying the frequency of the carrier signal linearly with the message signal. Phase modulation is another type of angle modulation very similar to frequency modulation.
808 1183 689 1607 1568 960 709 310 922 1463 1513 553 1515 1033 1469 249 348 302 187 988 142 1589