Theory frequency demodulator is a circuit which converts instantaneous frequency variations to linear. 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. The demodulation module involves division and arctan for which there is no dedicated hardware on a fixedpoint dsp. Using a phaselockedloopfor fm demodulation a device called a phaselockedlooppll can be used to demodulate an fm signal with better performance in a noisy environment than a frequency discriminator. As the amplitude increase the frequency decreases and vice versa. The example, shows how the fm modulator baseband and fm demodulator baseband blocks are used to modulate and demodulate a sinusoidal signal. Each type has its own advantages and disadvantages, some being used when receivers used discrete components, and others now that ics are widely used. Abstract this paper addresses the fixedpoint dsp implementation of fm demodulation and decoding for the digital radio application. Refer to the circuit diagram in figure 76 or figure acs72 on etek acs300004 module to produce the demodulated fm signal as the signal source. To understand the theoretical foundations for angle modulation as well as frequency modulation fm and demodulation. The fm is a very popular technique since they are widely used by the fm radio stations. Fm demodulator in the presence of both speckle noise which is multiplicative and additive noise and discuss the.
Communication fundamentals envelope of a bandpass signal a signals gt is a bandpass signal if its fourier transform is nonnegligible only in a band of frequencies of total extent 2w centered about fc. Slope detector fm demodulation balanced slope detector. Fm demodulation is also called fm detection and sometimes the phrase fm discrimination is used, although this term tends to be used with older circuits and technology. 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. Modulation and demodulation medium, it would be dif.
Fm modulation introduction in this lab, you will investigate frequency modulation fm and its properties. The analytical signal for an analog frequency modulated fm signal is. Demodulation of fm is done by frequency discrimination method and phase discrimination method. In chapter1, we investigated the way of modulating a sinusoidal carrier wave using am technique. Fm signals have the same peak frequency deviation, then. As we have seen in this document, frequency modulation can be simplified to angle modulation with a simple integrator.
Its adjustment free modulationdemodulation circuit significantly reduces the number of peripheral circuits required and can contribute to lower production costs. The fm demodulator option allows triggering to the demodulated signal. Fm demodulation in the presence of multiplicative and. Amplitude modulation, am frequency modulation, fm double and single sideband, dsb and ssb digital modulation phase shift keying. Implementation of fm demodulator algorithms on a high performance digital signal processor tms320c6711 dsp franz schnyder christoph haller 11. There are many types of modulation so there are many types of demodulators. 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. However if st is sinusoidal, then the instantaneous frequency deviation of the anglemodulated signal is. A simple and effective fm demodulation technique involves a highpass filter for fmtoam conversion followed by an am demodulator. A pll should have basic functional blocks like voltage controlled oscillator vco, phase comparator, low. There are a number of circuits that can be used to demodulate fm. In this chapter we will discuss ways of demodulating am, cw, fm, phase, and pulse modulation.
Understanding quadrature demodulation radio frequency. In the modulating process the carrier wave is generated by the lo circuit, and then combined with the baseband signal inside the mixer. Fm demodulation circuit as the amplitude variations occurs in the sine wave the frequency generated by the 555 changes and hence a frequency modulated wave is obtained at the output of the 555 ic. The circuit in which restoration is achieved is called the detector or demodulator both of these terms are used in neets. All digital fm demodulator kartik nair vtechworks virginia tech. The display is stable if a minimum of five modulation periods are within the recording time. To implement the simulink models for fm including a basic sinusoid and a multimedia file music to analyze each signal in time and frequency domains using time scope and spectrum analyzer. The fmmodulated signal has its instantaneous frequency that varies linearly with the amplitude of the message signal. Demodulation is extracting the original informationbearing signal from a carrier wave. Implementation of fm demodulator algorithms on a high performance digital signal processor tms320c6711 dsp franz schnyder christoph haller. Fixedpoint dsp implementation of fm demodulationdecoding.
The main reason behind using the fm modulations by the radio stations is. The goal of this experiment is to become familiar with fm modulation and demodulation. Digital and fm demodulation of a doublyclamped single wall. Describe fm demodulation circuit operation for the phaseshift and gatedbeam discriminators and the ratiodetector demodulator. The la72912v is a fm modulation and demodulation singlechip ic. One approach to reduce this interference, known as frequencydivision multiplexing, allocates different carrier frequencies to different users or for dif. B n0 2 df 2bn0 the transfer function for fm demodulator satis. Other methods of fm demodulation include a phase locked loop pll demodulator, and various arrangements using tuned circuits once popular, but no longer in these days of miniature, integrated circuit implementations. Consider a frequency modulated signal fed to a tuned circuit whose resonant frequency is to one side of the center frequency of the fm signal. After the introduction of basic principle, we build a fm demodulation hardware test platform based on sdr. Demodulation of fm slope and balanced slope detector. There are a number of circuits that can be used to.
Therefore the following block diagram is the frequency discrimination fm demodulator. Frequency modulation is widely used for fm radio broadcasting. Introduction frequency modulation fm has a long history of its application and is widely used in radio broadcast. Pdf amfm demodulation methods for reconstruction, analysis.
In this experiment you will demodulate the fm signal using either slope detector or phase locked loop pll. Once the signal has been received, filtered and amplified, it is necessary to recover the. An fm signal needs an additional stage called a discriminator that converts frequency into an amplitude signal. A noncoherent detector has only one input, namely, the modulated signal port. Labview programming and interfacing to usrp was done. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam.
It is this process that is called demodulation or detection. A fm quadrature demodulation method based on small angle. The term demodulator is used because the demodulation process is considered to be the opposite of modulation. This work discusses the demodulation scheme for one of the most widespread modulation algorithms, frequency modulation fm. Frequency modulation fm is an important modulation scheme both because of its widespread commercial use, and because of its simplicity. To illustrate the concept of fm demodulation using a. A bandpass filter isolate the fm signal with carrier frequency n. Experiment to determine fm demodulation objective the main objective of the experiment was to.
Implementation of fm demodulator algorithms on a high. 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. Pdf labview interfacing usrp for fm demodulation wai. In addition to audio signal, it can also be used in data pulse. However, an unfortunate byproduct of differentiation is that it amplifies highfrequency noise and degrades the overall signaltonoise ratio snr of the recovered message signal. If youve read the page on amplitude demodulation, the preceding paragraph may have caused you to realize that a quadrature demodulator is actually composed of two amplitude demodulators. It is also used in telemetry, radar, seismic prospecting, and monitoring newborns for seizures via eeg. Frequency modulation fm is a technique in which the frequency of a transmitted waveform is varied according to the variations in the message wave. Slope detector can be constructed with the help of a tuned amplifier and an envelope detector. Fm demodulation is a key process in the reception of a frequency modulated signal. The fm demodulator is done with the help of a circuit called phase locked loop pll.
Frequency modulation consists of encoding information onto a carrier signal by varying the frequency of the carrier. The block diagram of a discretetime version of a pll is shown in the. This method all digital demodulation can be used for for fm signal. Demodulate fm signal using fm to am conversion discriminator. If the message was a single tone, from its amplitude can you estimate the frequency deviation of the fm. Of course, you cannot apply ordinary amplitude demodulation to a frequency modulated signal. The output of this tuned circuit will have an amplitude that depends on the frequency deviation of the input signal. In an earlier semester project, four fm demodulation algorithms were developed and tested on their suitability. Once the signal has been received, filtered and amplified, it is necessary to recover the original modulation from the carrier. Communication theory of fm demodulation was practically approach in this paper.
The pll is examined in the lab sheet entitled fm demodulation by pll. Some phase modulation and quadrature amplitude modulation formats have a higher spectral efficiency for data transmission than frequency shift keying, a form of frequency modulation. Frequency modulation fm is a process in which the carrier frequency is varied by the amplitude of the modulating signal i. Functions ask modulation and demodulation video signal fm modulation and demodulation. Slope detector fm demodulation that is illustrated in figure 633. Pdf in this paper, we present new 3d amplitudemodulation frequency modulation amfm methods for video image analysis.
During this lab you will create an fm signal by modulating an audio waveform onto a carrier, examine the spectrum of the modulated carrier, evaluate the modulated carrier when the modulation index is varied and. Once a signal has been modulated, information is retrieved through a demodulation process. Noise and fm suppose that the power spectrum of noise is. A phaselocked loop can be used to achieve highperformance fm demodulation. Index terms demodulation, envelope, coherent, squarelaw, fm to am, zerocrossing. Division is normally achieved either by using the newtonraphson method or by. Dutton ee3 winter 2004 3 3 fm demodulation using the pll now that youve seen how the pll tracks a signal, we will explore one of its applications, fm demodulation.
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