Thus when the frequency modulated wave is applied at. There are many types of modulation so there are many types of demodulators. You are free to choose the frequency and magnitude of the carrier and message signals. If the message was a single tone, from its amplitude can you estimate the frequency deviation of the fm. Frequency modulation fm is the standard technique for highfidelity communications as is evident in the received signals of the fm band 88108 mhz vs. Fixedpoint dsp implementation of fm demodulationdecoding h. Fm modulated signal st is a nonlinear function of the modulating signal mt, thus it is known as nonlinear modulation process. The bandwidth is set wide enough to pass the transmitted signal provides adjacent channel rejection. This method is shown to be effective with respect to speed.
Fm stereo is widely used in vehicular transceiver9, mobile communication system10 and so on, and fm stereo receiving is often used in broadband wireless receiver, so the paper research fm stereo receiver based on software defined radio. Frequency modulation equations formulas bessel rf cafe. Finally, fmstereo multiplex operation will be introduced as an example of an early form of combinational modulation used to send more. A simple yet effective fm demodulator is one which takes a time average of the zero crossings of the fm signal. If the input signal frequency changes, so does the carrier frequency. Demodulation is extracting the original informationbearing signal from a carrier wave. Fixedpoint dsp implementation of fm demodulationdecoding. To keep the compatibility the new device should be able to perform the analog modulation. The exciter section contains the carrier oscillator, reactance modulator and the buffer amplifier. Fm radio the bandwidth of an audio signal speech and music in is almost 15 khz. Explain the advantages and disadvantages of the different analog modulation techniques. Fm demodulator circuits are found in any receiver that uses fm. Xr2212 is a highly stable, monolithic pll phase locked loop ic specifically designed for communication and control system applications. In this second experiment, we will examine the most common modulation scheme in daily life, namely, the frequency modulation, or fm.
Calculate modulation index, signal bandwidth, sideband frequencies and. Please see the fundamentals of analog communications section as discussed in the first experiment as a reference. An fm signal, and a train of zerocrossing pulses each pulse in the pulse train is of fixed width, and is located at a zero crossing of the fm signal. Discuss the differences between am and angle modulation. Modulation index definition is a measure of the degree of frequency modulation expressed numerically for a pure tone modulation as the ratio of the frequency deviation to the frequency of the modulating signal. However if st is sinusoidal, then the instantaneous frequency deviation of the anglemodulated signal is. 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. Slide 6 narrow band fm slide 7 bandwidth of an fm signal slide 8 demod.
Fm demodulation with the pll a2 143 t5 measure the properties of each element of the pll, and then predict some of its properties as a demodulator. In the laboratory, you will use function generator as vco. What is fm, frequency modulation electronics notes. Fm transmitter fm transmitter block diagram direct method. Fm signals have the same peak frequency deviation, then. To extend the range of sound, we need to transmit it through a medium other than air, such as a phone line or radio. Frequency modulation objectives upon completion of this chapter, the student should be able to. Even though there are different methods for modulation and demodulation processes, each has its own advantages and disadvantages. In frequency modulation fm, unlike am, the amplitude of the carrier is kept constant, but its frequency is altered in accordance with variations in the audio signal being sent. In any radio that is designed to receive frequency modulated signals there is some form of fm demodulator or detector.
Implementation of fm demodulator algorithms on a high performance digital signal processor. 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. Angle modulation is the process in which the frequency or the phase of the carrier varies according to the message signal. To generate a frequency modulated signal, the frequency of the radio carrier is changed in line with the amplitude of the incoming audio signal. However, modulation is extensively used in most communication systems. Fm is mostly used in highfrequency radio broadcasting, and pulse modulation is known for digital signal modulation. The main reason for the improved fidelity is that fm detectors, when properly designed, are not sensitive to random amplitude variations which are the. Fm is mostly used in highfrequency radio broadcasting, and. The amount of change in frequency is determined by the amplitude of the modulating signal. Frequency modulation university of california, berkeley. In general, the problem of determining the amplitude and frequency modulations am and fm of a signal is ill posed because there is an unlimited number of combinations of am and fm that will.
An fm transmission consists of a wave whos frequency is modulated, or changed, with respect to an input signal. The process of modulation in a communication system increases its cost and complexity. Know the relationship of carrier frequency, modulation frequency and modulation index to efficiency and bandwidth compare fm systems to am systems with regard to efficiency, bandwidth and noise. This form of modulation was developed by the american electrical engineer edwin h.
The angle modulated signal described in time domain. Modulation index definition of modulation index by merriam. This application note is designed to show fm data transmission and modulation using some common test instruments. A demodulator is an electronic circuit or computer program in a softwaredefined radio that is used to recover the information content from the modulated carrier wave. This is further divided into frequency and phase modulation. In audio and music frequency modulation synthesis or fm synthesis is a form of audio synthesis where the timbre of a simple waveform is changed by frequency modulating it with a modulating frequency that is also in the audio range, resulting in a more complex waveform and a differentsounding tone. 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. This is based on a dsp, using dsp for demodulation of ssb, variable bandwidth filters, agc, noise reduction etc. Three fm demodulation methods frequency discriminator slope detector balanced freq. Frequency modulation uses the instantaneous frequency of a modulating signal voice, music, data, etc. The subsystem that takes the information signal and processes it. Frequency modulation frequency modulation is the process by which frequency of the carrier signal ct changes with respect to the modulating signal mt. Modulation and demodulation techniques request pdf. Abstract analog modulations are more and more replaced by digital ones.
A novel demodulation scheme for pskfm command signal based on dsss technique. Slide 3 discretetime fm modulator slide 4 single tone fm modulation slide 5 single tone fm cont. Frequency response of a single tuned circuit and b stagger tuned circuit method of converting an fm signal to an am signal will be to exploit the frequency response characteristic of a single tuned circuit. Pdf a novel demodulation scheme for pskfm command signal. Modulation index definition is a measure of the degree of frequency modulation expressed numerically for a pure tone modulation as the ratio of the frequency. La72912vd la72912v fm modulator and demodulator ic overview the la72912v is a fm modulation and demodulation singlechip ic. Modulation index definition of modulation index by. Sep 20, 2012 frequency modulation frequency modulation is the process by which frequency of the carrier signal ct changes with respect to the modulating signal mt. When the audio signal is modulated onto the radio frequency carrier, the new radio frequency signal moves up and down in frequency. But for fm demodulation kenwood have chosen to convert to another if frequency 455 khz and add an fm demodulator chip.
Implementation of fm demodulator algorithms on a high. Fmam conversion using stagger tuned amplifier a b fig. In this experiment you will demodulate the fm signal using either slope detector or phase locked loop pll. May 05, 2011 this is based on a dsp, using dsp for demodulation of ssb, variable bandwidth filters, agc, noise reduction etc. The fmmodulated signal has its instantaneous frequency that varies linearly with the amplitude of the message signal. Experiment4 frequency demodulator preliminary work 1. Fm modulation system fm transmitter, reactance modulator. Its adjustment free modulationdemodulation circuit significantly reduces the number of peripheral circuits required and can contribute to lower production costs. Frequency and phase modulation sharlene katz james flynn overview history why fm. The envelope contains a residual amplitude modulation that varies with time the angle contains harmonic distortion in the form of third. When implemented in q30 representation, the snr is expected to be further increased. Then retune the transformer so that the fm carrier frequency falls at 455 khz. Frequency modulation is the process of varying the frequency of the carrier signal linearly with the message signal. Lets assume that by looking at the transfer curve obtained, you have decided that the fm carrier should fall at 452 khz.
If the message was a single tone, from its amplitude can you estimate the frequency deviation of the fm signal. All they use the dsp for on fm is for audio processing. This means that, in order to move the fm carrier up to 455 khz, the whole response curve. For example, am is used in shortwave and radio wave broadcasting. A simple pll fm demodulator circuit using ic xr2212 is shown here. Amplitude distortion of narrowband fm ideally, fm wave has a constant envelope but, the modulated wave produced by the narrowband fm differ from this ideal condition in two fundamental respects. To improve the quality of reception to increase the range of communication need of demodulation the wireless signal consists of radio frequency high frequency carrier wave modulated by audio frequency low frequency. Fm radio receiver with digital demodulation a senior project presented to the faculty of the electrical engineering department california polytechnic state university, san luis obispo. Basic concepts of modulation three kinds of modulations modulation is the process of facilitating the transfer of information over a medium.
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