Let us consider the expression for fm wave as under. Curriculum theory in digital signal transmission, the repeater is used to recover the data signal, this will enhance the immunity to noise. An introduction to frequency modulation sound on sound. With no modulating signal present, the circuit operates as a linear class a amplifier, and the output is simply the carrier. The tracking voltage is therefore a replica of the fm modulation signal. Carrier modulation allows the transmission of modulating frequencies without the use of transmission wire as a medium. Modulators circuits and tutorials 12 volt or 24 volt dc pulse width modulator. Frequency modulation objectives upon completion of this chapter, the student should be able to. 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. Fm modulation is also easy, but a little harder to conceptualize if youre not fluent with electronics. Frequency modulation tutorial and fm radio transmitter. There are two common forms of angle modulation, namely, phase modulation and frequency modulation.
Review pulse train bandwidth s ingle pulse of duration. Modulator electronic circuits, schematics or diagrams links. Amplitude modulation am up to 99% is available on the 11 to. This video explains what frequency modulation fm is and shows a simple low powered fm radio transmitter circuit you can build. Pdf nonlinear frequency and amplitude modulation of a. Phase modulation and frequency modulation have many similarities and are linked one is the differential of the other. Gcse students might find it interesting as they are often playing with the 555 timer ic. To understand the operation theory of fsk modulator. The term and technology us used in both telecommunications and signal processing 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. Capacitor microphone fm generator simplest fm generator transmitter refer to fig 51 next slide lc tank and oscillator generate sinewave output that goes to antenna capacitance on lc tank is a capacitor microphone aka condenser mike frequency of impinging sound waves intelligence determines the rate of output frequency change amplitude of impinging sound waves. To extend the range of sound, we need to transmit it through a medium other than air, such as a phone.
Fm modulation and demodulation circuit multisim live. One approach to reduce this interference, known as frequencydivision multiplexing, allocates different carrier frequencies to different users or for dif. To understand the fsk modulation by using the theory of mathematical. The modulator and demodulator circuits were designed and simulated later on using multisim. There are many ways in which amplitude modulation can be generated and a variety of circuits that can be used. The subject is new and all of its ramifications and prob lems are not known as yet, hence this volume of compara tively few pages is not intended as a complete exposition of the subject. Lecture 4 frequency modulation frequency modulation. Explain the difference between narrow band fm and wide. For instance, the crackling form of radio interference caused by natural lightning or the buzzing noise produced by highvoltage power lines are both easy to hear on an am radio, but absent on an fm radio. Read about the many types of radio frequency modulation radio frequency modulation. This will absolutely beneficial to those aspiring to become professional engineers by taking the board exam and eventually to become successful in their chosen field. This chapter describes the essential principles behind.
Explain the advantages and disadvantages of the different analog modulation techniques. 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. Hes broken down the modulation and demodulation circuits into their basic opamp stages with examples of what the signal should look like on a. Spectra have a typical trapezoidal shape in linear frequency and amplitude in decibels.
Mar 01, 2016 the term k f x t represents the frequency deviation. Basic concepts of modulation three kinds of modulations modulation is the process of facilitating the transfer of information over a medium. Am1 a2 selecting pitch selecting the high cutoff in other modes selecting the low cutoff in other modes adjusting the volume adjusting the press and choose the desired modulation type by rotating the tuning knob. What is fm, frequency modulation electronics notes. The spectrum is a series of diracimpulse spaced by nfm and multiplied by the. The pdf describes a reyliegh distribution, where as pdf describes a uniform.
Lecture 4 frequency modulation free download as powerpoint presentation. The low pass filter comprised of the rc circuit is designed to have cutoff frequency as the. Fm signals have the same peak frequency deviation, then when mt is a sinusoidal signal set such that the pm and note. The spectrum of an fm signal is quite complicated and is dependent on mf. As the name indicates, phase modulation varies the phase of the carrier in line with the modulating signal. The demodulation of a fm signal requires a circuit that yields an output voltage that varies linearly proportional to the frequency deviation of the input.
Hi in nfm the modulation index is very low, much lower than 1. Based on the location in the transmitter am modulating circuits are classified as a. The message signal is, for example, a function of the sound to be reproduced by a. Xr2212 is a highly stable, monolithic pll phase locked loop ic specifically designed for communication and control system applications. In this radiomaster reports article, we unravel the secrets of fm modes and explain how to know when to use nfm and fm. On the shortwave band this active antenna is comparable to a20 to30 foot wire antenna. You can use our 555 astable multivibrator calculator in the bottom of the article astable multivibrator using 555 timer for easy calculations.
The various parts of this lab unit will be used to explore and verify the operation of the two am modulation methods using four different am modulating circuits. Amplitude modulation am 9 t15 use speech or music from trunks as the message, and show that this also generates a trapezoid, and that setting the message amplitude so that the depth of modulation reaches unity on peaks a triangle is especially easy to do, using the gain control g of the adder. Here is a frequency modulation fm circuit that uses a 555 timer in astable mode to generate a sine wave carrier. Modulationtypesamplitude,frequency,phase modulation. An important feature of angle modulation is that it can provide better. While changing the amplitude of a radio signal is the most obvious method to modulate it, it is by no means the only way. Hes broken down the modulation and demodulation circuits into their basic opamp stages with. Dear forum members, i am working as the application engineer. Frequency modulation is the process in which the frequency of the carrier signal is varied by the modulating signal while the amplitude remains constant. In an arq system, when a receiver circuit detects parity errors in a block of data, it requests that. It is also possible to change the frequency of a signal to give frequency modulation or fm. To design and implement the fsk modulator by using vco. Modulators circuits electronics tutorial and schematics.
As the frequency rises and falls the tuned circuit provides a changing amplitude of response. Peter 8 years ago i have gone through this peace and am happy. Frequency modulation fm is the encoding of information in a carrier wave by varying the. Fm tends to be a far more noiseresistant means of signal modulation than am. Tcom 370 notes 995 modulation and demodulation modems for. Pdf slow scan television sstv image transmission system is used by many decades by radio. Again, the frequencies of the sidebands are satisfying the expected theoretical results fcnfm.
This circuit can be used as a light dimmer or dc motor speed controller. Calculate modulation index, signal bandwidth, sideband frequencies and. Spectrum of a pm or fm signal with sinusoidal modulation. Fm versus nfm for best radio communications radiomaster. Frequency modulation fm is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. Thitimajshima p 2010 near shannon limit errorcorrecting pdf. Coupling capacitor c3 is designed in such a way that it can couple the input message signal.
Modulation and demodulation medium, it would be dif. There are two types of fm modulators direct and indirect. However phase modulation lends itself to data transmissions, and as a result its use has grown rapidly over recent years. The term and technology us used in both telecommunications and signal processing 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. In an emergency, you may need to communicate with others by radio the original source of this article is radiomaster reports. Recall that our goal is to transmit data over a commu nication link, which we achieve by mapping the.
Modulation is explained along with detailed description of its types like amplitude modulation,frequency modulation ad phase modulation. Discuss the differences between am and angle modulation. Lecture notes on analogue communication techniques. In addition to audio signal, it can also be used in data pulse.
For small values of k f, the frequency deviation is small and the spectrum of fm signal has a narrow band. We are now ready to explore a fundamental aspect of rf engineering. The possibilities expand still further when we consider what happens when you use one audiofrequency signal to modulate the frequency of another. Lecture 2829 fm frequency modulation pm phase modulation. As explained last month, audiofrequency modulation of the amplitude of a signal can be a powerful synthesis tool. Even for sinusoidal modulation the number of side frequency pairs is theoretically infinite. Features y excellent carrier suppression 65 db typical. Slide 3 discretetime fm modulator slide 4 single tone fm modulation slide 5 single tone fm cont.
Nfm is the frequency range of an individual in the absence of deemphasis. The modulating signal varies the capacitance of the diode, which then changes the phase shift incurred by the carrier input and thus changes the phase of the output signal. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. Transmitters that transmit amplitude modulated signals require an am modulator circuit to produce the required signal. Narrowband frequency modulation nfm was a relatively new. Nfm is mainly used for speech communication systems like ham radios and police and other type of communication except airplane vhf communications, they use am for a very good reason. Frequency modulation fm circuits electronics teacher.
Since the phase change across a tuned circuit of q 10 or higher is fairly. Pm and digital modulation s p where 2 is the pkpk phase change in one symbol duration, t for digital signals the modulation index. A varactor diode circuit for indirect fm is shown in figure 3. Fm modulation jie liang school of engineering science simon fraser university 1. Fm modulationdemodulation with pll general description package outline njw2307 is a fm modulation demodulation ic for audio signal in full duplex communication that operates from 3. The many types of radio frequency modulation radio. Describe phase demodulation circuit operation for the peak, lowpass filter, and conversion detectors. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. Amplitude modulation am 9 t15 use speech or music from trunks as the message, and show that this also generates a trapezoid, and that setting the message amplitude so that the depth of modulation reaches unity on peaks a triangle is especially easy. Category advanced tutorials tag frequency modulation modulation radio electronics radio transmitter rf. Hapter modulation and demodulation mit opencourseware. Introduction in chapters 1 and 2 you studied how to apply intelligence modulation to an rfcarrier wave.
Frequency modulation is widely used on frequencies above 30 mhz, and it is particularly well known for its use for vhf fm broadcasting. However if st is sinusoidal, then the instantaneous frequency deviation of the anglemodulated signal is sinusoidal. Slide 6 narrow band fm slide 7 bandwidth of an fm signal slide 8 demod. Because the phase of the carrier is shifted, the resulting signal has a frequency which is. This book presents a comprehensive overview of the various modulation tech. Specialized rf source description frequency modulation the agilent technologies model 11715a am fm. Can any one send me the collector modulation circuit for the am. In early am transmitters the amplitude modulator circuit was a key element of the transmitter. A simple pll fm demodulator circuit using ic xr2212 is shown here. This circuit shows an active antenna that can be used for am, fm, and shortwave sw. Pdf long range image radio transmitter researchgate. The carrier amplitude is constant and the phase variation of the signal contains the information.
994 1414 1174 119 60 197 875 1224 833 688 1244 384 1540 1227 855 1123 689 987 280 746 739 454 995 1524 157 1250 917 953 252 1236 1356 1245 534 1249 767 1134 721 749 634 29 629 183 1233 111 1077 948 51 674 1412