Introduction in chapters 1 and 2 you studied how to apply intelligence modulation to an rfcarrier wave. We will assume that the baseband message signal mt is band limited with a cuto. In the earlier time of wireless communication, it was measured that the required bandwidth of this was narrower, and necessary to decrease noise as well as interference. Look at the signal generator manual to see how to get an fm signal. Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation. This principle is at the heart of amplitude modulation. Fm modulation with modulating frequency 1, carrier frequency 10 and modulation index 2. That could be the amplitude, phase, or frequency, which result in amplitude modulation am, phase modulation pm, or frequency modulation fm. The frequency spectrum of a typical radio signal from an am or fm radio transmitter. In the technique of frequency modulation the frequency of a carrier wave is modulated according to the variations in the amplitude of the message wave. In amplitude modulation only the amplitude of the carrier changes as we can see above for both binary and analog messages. Modulation is the process whereby message information is embedded into the radio frequency carrier. The first practical system was put forward in 1936 as an alternative to am in an effort to make radio transmissions more resistant to noise. However if st is sinusoidal, then the instantaneous frequency deviation of the angle modulated signal is.
Frequency modulation fm was invented and commercialized after amplitude modulation. Modulation for frequency assignment the fcc assigns frequency bands to each radio application. The goal of this experiment is to become familiar with fm modulation and demodulation. 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. These methods contrast with amplitude modulation, in which the amplitude of the carrier wave varies, while the frequency and phase remain constant. Pdf detection of frequency modulation by hearingimpaired. Frequency modulation fm is a variation of angle modulation where instead of phase, we change the frequency of the carrier in response to the message signal. Basic concept of modulation the information source typically a low frequency signal referred to as the baseband signal carrier a higher frequency sinusoid example. Frequency modulation is a form of analog angle modulation in which the baseband informationcarrying signal, typically called the message or information signal mt, varies the frequency of a carrier wave.
Therefore, both fm and pm are often referred to as angle modulation. For fm, the percentage of modulation is the ratio of the actual frequency deviation and the maximum allowed frequency deviation. In this experiment, you will examine the characteristics of amplitude modulation am. If the baseband signal is bandlimited, then there is a. The fm or frequency modulation has been available approximately since am amplitude modulation although it has only some issues. Carrier modulation allows the transmission of modulating frequencies without the use of transmission wire as a medium. The sound quality offered by am radio stations is poorer, having low. The process of phase modulation is somewhat the same as that of frequency modulation. The synthesis of complex audio spectra by means of frequency. Ordinarily, the carrier frequency is much greater than the symbol rate of the modulation, thoughthis is notalwaysso. This increasing bandwidth as i increases, is shown in fig.
In frequency modulation, the instantaneous frequency of the carrier wave is modified in order to transmit information. There are various forms of modulation, each designed to alter a particular characteristic of the carrier wave. For a 1 khz sinusoidal baseband signal tone modulation and 10 khz carrier f hz. Pm and digital modulation s p where 2 is the pkpk phase change in one symbol duration, t for digital signals the modulation index. Thus, ssb modulation requires half the bandwidth of am or dsbscam modulation. The basic theory and equations behind amplitude modulation are relatively straightforward and can be handled using straightforward trigonometric calculations and manipulation. Modulation, in electronics, technique for impressing information voice, music, picture, or data on a radiofrequency carrier wave by varying one or more characteristics of the wave in accordance with the intelligence signal. 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. In particular, we discuss amplitude and frequency modulation. A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. It consists of a signal c at the carrier wave frequency fc, with the modulation contained in narrow frequency bands called sidebands sb just above and below the carrier.
Chapter 8 frequency modulationfm fm was invented and commercialized after am. Audio signals transmitted by fm radio communications are the most common. Know the relationship of carrier frequency, modulation frequency and modulation index to efficiency and bandwidth. Polar view of digital iq modulation contd transmission signal is sine wave at frequency f 0 with information encoded in discrete values of amplitude and phase. Learn various types of amplitude and frequency modulation methods from modulation degree and sideband amplitude, zero span and markers and more. Vary the frequency by adding a time varying component to the carrier frequency. 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. Inmany digitalcommunications systems, the analog carrier is at a radio frequency rf, hundreds or thousands of mhz, with information symbol rates of many megabaud.
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. Principles of communication modulation tutorialspoint. The baseband signals are incompatible for direct transmission. The interaction of carrier frequency and modulation rate was also signi. Once a signal has been modulated, information is retrieved through a demodulation process. Any baseband signal can be broken up into a weighted sum of sinusoids using fourier decomposition chapter. Frequency modulation fm is a process in which the carrier frequency is varied by the amplitude of the modulating signal i. Difference between amplitude modulation and frequency modulation. There are two reasons why frequencydivision multiplexing works. With frequency modulation, we use the integral of x bb, which has the effect of shifting the high or low frequency carrier sections to the baseband values following the high or low slope portions of the baseband waveform. Chapter 7 singlesidebandmodulationssb andfrequency. In amplitude modulation or am, the carrier signal has its amplitude.
Its main advantage is that it is more resistant to additive noise than am. Fm is considered an analog form of modulation because the baseband signal is typically an analog waveform without discrete, digital values. There is another way of modulating a, sinusoidal carrier wave, namely, angle modulation in which the angle of the carrier wave is varied according to the baseband signal. Amplitude modulation early radio ee 442 spring semester. If the unmodulated carrier signal is represented by a sin2pf t and the modulating signal is represented by b sin2pfa t. 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.
The main advantage of the frequency modulation technique is the very high signal to noise ratio that can be achieved on the received signals. Fm is a so called angle modulation scheme, it was inspired by phase modulation but has proved to be more useful partly for its ease of generation and decoding. A simple method to achieve fm is to vary the capacitance of a resonant lc circuit in a transmitter. To generate a frequency modulated signal, the frequency of the radio carrier is changed in line with the amplitude of the incoming audio signal. Frequency modulation consists of encoding information onto a carrier signal by varying the frequency of the carrier. A n ovel random carrier frequency modulation technique for drive applications c. Modulation for ease of radiation antennas must be greater than onetenth of the wavelength 10. The carrier or sideband amplitudes are zero at some modulation indexes 20. Oct 05, 2015 amplitude modulation and frequency modulation are both methods of modifying a carrier signal in order to transmit data. In amplitude modulation, the amplitude of the carrier wave is modified in order to transmit information. For such a signal, to travel longer distances, its strength has to be increased by modulating with a high frequency. Fm modulated signal st is a nonlinear function of the modulating signal mt, thus it is known as nonlinear modulation process. Difference between amplitude modulation and frequency. Signals that interfere with an intentional electronic broadcast are called static, and static is the main drawback of am radio.
Phase modulation pm is a different form of frequency modulation and the carrier is similar in appearance to a frequencymodulated carrier. The instantaneous frequency of an fm wave with carrier frequency. There are two ways to calculate the bandwidth of an fm 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. Message information can be transmitted in either the amplitude, frequency, or phase of the carrier, or a combination thereof, in either analog or digital format. In analog applications, the carrier frequency is varied in direct proportion to changes in the amplitude of the data signal, as shown in figure 2.
Frequency modulation fm is the method of conveying informations over a carrier wave by varying its frequency. In modulation, one characteristic of a signal generally a sinusoidal wave known as the carrier is changed based on the information signal that we wish to transmit modulating signal. Time frequency time domain plot frequency domain rf carrier f c, e. Spectrum analysis amplitude and frequency modulation. Modulation is the process of changing the parameters of the carrier signal, in accordance with the instantaneous values of the modulating signal. Difference between amplitude modulation and frequency modulation type of modulation. Frequency modulation fm is the modulation technique that represents information as variations in the frequency of the carrier wave, whereas in am, the carrier amplitude is varied while its frequency remains constant. Oct 12, 2018 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. What is fm, frequency modulation electronics notes. Fm signals have the same peak frequency deviation, then when mt is a sinusoidal signal set such that the pm and note. Theory of frequency modulation and phase modulation. Modulation, in electronics, technique for impressing information voice, music, picture, or data on a radio frequency carrier wave by varying one or more characteristics of the wave in accordance with the intelligence signal.
The bandwidth of an fm signal is proportional to the modulation index 21. This is different from the amplitude modulation am in which the amplitude of the carrier wave is varied while its frequency remains constant. As whenever there is any variation in the phase of the carrier signal, then, the frequency of the signal also shows variation. The synthesis of complex audio spectra by means of. Different carrier frequencies are used to meet this need. To counteract static, a better method of superimposing information on a radio wave, called frequency modulation or fm, was developed in 1933. Fm itself didnt have a problem apart from we couldnt recognize the fm transmitter potential. When the audio signal is modulated onto the radio frequency carrier, the new radio frequency signal moves up and down in frequency. J ar in 2 1 assistant professor, department of eee, jy othi engineering college, thrissur, kerala. Frequency modulation frequency modulation is the process by which frequency of the carrier signal ct changes with respect to the modulating signal mt.
The telephone company invented modulation to allow phone conversations to be transmitted. Pdf a novel random carrier frequency modulation technique. Describe phase demodulation circuit operation for the peak, lowpass filter, and conversion detectors. This is called frequency shift keying fsk and is a digital format. In phase modulation, the amplitude of the carrier signal remains unchanged while phase change occurs. Frequency modulation fm is a form of modulation in which changes in the carrier wave frequency correspond directly to changes in the baseband signal. In frequency modulation, the intensity of the carrier wave isnt varied. In chapter1, we investigated the way of modulating a sinusoidal carrier wave using am technique.
The index of modulation of an fm signal of the form. Instantaneous frequency the instantaneousfrequencyof cos. In pm, the phase shift of the carrier is varied by the amplitude of the modulating signal. Frequency modulation and phase modulation are the two complementary principal methods of angle modulation. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation. Analog modulation schemes include amplitude modulation am and frequency. The main difference between amplitude modulation and frequency modulation is that, in amplitude modulation, the amplitude of the carrier wave is modified according to the data whereas, in frequency modulation, the frequency of.