To study and perform pulse position modulation and demodulation. In theory, an ideal frequency modulation fm detector is a device that produces an output that is proportional to the instantaneous frequency of the input. Lab procedure for fm demodulation 1 build the slope detector. 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.
Pll and frequency demodulation 3 when signals have different values, we should change frequency of the vco. To understand the theoretical foundations of analog communications as well as of doublesideband amplitude modulation and demodulation dsbam to design the simulink model of the dsbam to analyze each signal in time and frequency domains using time scope and spectrum analyzer. The following diagram shows a simplified slope detector circuit. Demodulation of fm slope and balanced slope detector. In this video we will tell you about demodulation of fm slope and balanced slope detector. Amfm demodulation using hp 8566b spectrum analyzer kerry wong. Fm if system quadrature detector for car radio features 1. Build simple envelope detector for fm demodulation. Assuming we use a slope detector in place of the differentiator, draw the circuit diagram. After watching this video, you will be able to explain. Examine the factors affecting the shape of the spectrum and the bandwidth of fm signals. Any circuit that outputs the time derivative of the input can perform the fm to am conversion.
Here well examine how it is possible to demodulate these signals and recover the information. A noncoherent detector has only one input, namely, the modulated signal port. Circuit used suitable for envelope detector noncoherent diode with an rc. Balanced slope demodulator eec 112 the circuit belowisabalanced fm slope demodulator.
The am demodulator can be implemented by utilizing a balanced modulator. It is the process of deriving the original modulation signal from a modulated carrier wave. In an earlier semester project, four fm demodulation algo. The most basic phase lock loop used for fm demodulation consists of a phase detector, loop filter and a voltage controlled oscillator. Each channel sharing scheme a set of basis vectors. This view is not far from wrong because the operation of fm detectors is widely regarded as mysterious. Voltage controlled oscillator and fm frequency deviation. Slope detector fm demodulation that is illustrated in. Slope detector the slope detection is a method of fmdemodulation which converts the received fm signal to am and demodulates with an envelope detector.
The output of this tuned circuit will have an amplitude that depends on the frequency deviation of the input signal. The slope detector is a method of frequency demodulation which converts the received fm signal to am and demodulates with an envelope detector. Demodulation of fm is done by frequency discrimination method and phase discrimination method. Transmission of information page 1 of 8 experiment 5. The quadrature fm detector analysis and design introduction. Note that although well concentrate on fm demodulation, similar methods are useful for general measurements of signal frequencies and for pm demodulation. Laboratory manual principles of communication system lab ee226f ivth semester prepared by.
Principle any circuit that outputs the time derivative of the input can perform fm to am conversion. Fm radio receiver with digital demodulation a senior project presented to the faculty of the electrical engineering department. Voltage controlled oscillator and fm frequency deviation constant studying a voltage controlled oscillator vco is a good way to get introduced to frequency modulation concepts. Now connect the output of the previous circuit ic555 fm modulator, fig.
Dec 08, 2017 hi guys in this lecture fm demodulation. It is a detection technique of a received modulated signal. Slope detection is the very simplest form of frequency modulation, fm demodulation. Build simple fm demodulator by using frequency discriminator 2. For spectrum analyzers without the dedicated fm demodulation capability, we can use the slope detector method to do so. The signal output from a demodulator may represent sound an. This signal is then passed to an am detector, which uses a detector diode, d, as shown in figure a to recover the modulating signal, v o. To be able to understand the principles of operation for fm detectors, you need to first study the simplest form of frequencymodulation detector, the slope detector.
Distinguish between different types of fm signal 4. It is also used in telemetry, radar, seismic prospecting, and monitoring newborns for seizures via eeg, twoway radio systems, music synthesis, magnetic tape. Slope detector can be constructed with the help of a tuned amplifier and an envelope detector. Demodulation of fm slope and balanced slope detector rktcsu3e12 duration. Slope detector fm demodulation balanced slope detector. Describe fm demodulation circuit operation for the phaseshift and gatedbeam discriminators and the. Demodulate fm signals using a phaselocked loop pll.
The drawback of harmonic distortion is removed in this detector by using two slope detectors instead of one as in a singletuned slope detector. Monolithic linear ic la1145, 1145m fm if system quadrature. We call this type of modulator as synchronous detector or product detector. A coherent detector has two inputsone for a reference signal, such as the synchronized oscillator signal, and one for the modulated signal that is to be demodulated. 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. Implementation of fm demodulator algorithms on a high. The frequency of the vco is the unmodulatedcarrier frequency also. The envelope detector is an example of a noncoherent detector. Three fm demodulation methods frequency discriminator slope detector balanced freq.
To study and perform pulse code modulation and demodulation. Frequency modulation fm is a process in which the carrier frequency is varied by the amplitude of the modulating signal i. The very simplest form of fm demodulation is known as slope detection or. Implementation of fm demodulator algorithms on a high performance digital signal processor.
In frequency modulation, basically the frequency of the carrrier signal is changing with the instantaneous value of the baseband signal. Once the signal has been received, filtered and amplified, it is necessary to recover the. In this way the frequency modulated signal sits on the slope of the response curve, giving rise to the name of fm. If you find its useful dont forget to subscribe my channel also like it. Frequency discriminator jie liang school of engineering science simon fraser university. Restoring or recovering the message signal from the received modulated waveform that is generally corrupted by noise types of am detectors. Cme312 lab manual frequency modulation experiment 8. Jun 20, 2017 fm demodulation slope detection gate achievers. The drawback of harmonic distortion is removed in this detector by using two slope. In the part 12 we saw how it is possible to create signals which carry information by modulating the frequency or phase of a carrier wave. Slope detector ratio detector demodulation of fm waves. According to the principle of the slope detector, the received fm signal is applied to an lc circuit whose output is an amplitude and frequencymodulated signal. The envelope detector is a very simple method of demodulation that does not require a coherent demodulator.
Pll and frequency demodulation the pll phase locked loop describes the common way for generating a signal with a frequency which is in a fixed relation with the frequency of the reference signal like multiple. In this experiment you will demodulate the fm signal using either slope detector or phase locked loop pll. Disadvantages of using balanced slope detector for. Ratio detector for fm demodulation circuit wiring diagrams. 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. It consists of an envelope detector that can be a rectifier anything that will pass current in one direction only or other nonlinear component that enhances one half of the received signal over the other and a lowpass filter. To study and perform pulse amplitude modulation and demodulation. In part i you will learn how to design an amplitude modulator am and in part ii you will be able to demodulate an am signal.
Demodulation of fm slope and balanced slope detector slideshare. The slope detector is essentially a tank circuit which is tuned to a frequency either slightly above or below the fm carrier frequency. The goal of this experiment is to become familiar with fm modulation and demodulation. An fm slope detector consists of a tuned circuit where the centre frequency is tuned to a frequency slightly offset from the carrier of the signal. There are far more efficient methods that can be used for fm detection demodulation. Consider a frequencymodulated signal fed to a tuned circuit whose resonant frequency is to one side of the center frequency of the fm signal. Fm demodulation is a key process in the reception of a frequency modulated signal. The carrier frequency should fall on one side of resonant frequency and the entire frequencies should fall on linear region of transfer curve of tuned circuit. Lab manual frequency modulation experiment 8 experiment 2 objectives.
Consider a frequencymodulated signal fed to a tuned circuit whose resonant frequency is to one side of the. Frequency modulation and demodulation last modified. Slope detector the slope detection is a method of fm demodulation which converts the received fm signal to am and demodulates with an envelope detector. There are many types of modulation so there are many types of demodulators. When such an frequency modulated wave is transmitted at the transmitter, it has to be received at the receiver. The functional schematic of a quad detector is shown below in figure 1. By the end of this experiment, the student should be able to. Carsons rule and woodwards theorem use a 250 hz sine wave, square wave, and triangle wave to frequency modulate the hp3314a. What are the disadvantages of using balanced slope detector for demodulation of fm signal. The spectrum of an fm signal will also be examined.
Fm slope detection is a concept that can used be recover the modulation from an fm signal, but it is not widely used. Fm balanced slope detector construction, operation. Digital modulation and demodulation fsk,psk,bpsk,qpsk techniques. Demodulation is extracting the original informationbearing signal from a carrier wave. Remember, neither yt, nor the oscillator signal, appears at the multiplier output. To study and perform pulse width modulation and demodulation. This circuit has been used successfully for many years, but is not easy to build. Slope detection to be able to understand the principles of operation for fm detectors, you need to first study the simplest form of frequencymodulation detector, the slope detector. Fm balanced slope detector circuit circuit description. The diagram in figure 3 shows how these components are arranged.
To study and perform frequency modulation and demodulation. The fm wave is now coupled with a telescopic antenna for broadcast. Using matlab mfile and simulink to implement fm modulation and demodulation. It consists of a frequency to amplitude converter which in this case, is a simple tuned lc circuit.
View a of figure 39 is a plot of voltage versus frequency for a tank circuit. Dec 11, 2015 but how do we demodulate an fm signal. Fm balanced slope detector construction, operation, drawbacks. Lab procedure for fm demodulation 1 build the slope. Vhf oscillator and fm transmitter fm demodulation using pll in fm modulation when the bandwidth becomes so large that the input noise power is relatively large, the performance of the fm system degrades rapidly and the system exhibits a threshold. Basic fm demodulator the most basic circuit employed as fm demodulator is parallel tuned lc circuit, often known as slope detector. Aly elosery october 25, 2010 this lab is divided into two parts. In an fm signal the frequency is low, when the amplitude of the message signal is low and. Fm detection can be done using plls, or slope detection or quadrature detection. This brief paper addresses the techniques of quadrature detection.
Choose the amplitude of the message such that the maximum frequency deviation is 30 khz. Implementation of fm demodulator algorithms on a high performance digital signal processor tms320c6711 dsp franz schnyder christoph haller. The ratio detector to find out how it works, without going deeply into the theory at this point, or studying other forms of fm detector that are also used, and somewhat similar are covered here. A balanced slope detector is an improved version of the slope detector. In singlechannel efield sensing, the carrier we transmit is m, the sensed value is a, and the noise is n vectors. In an earlier semester project, four fm demodulation algorithms were developed and tested on their suitability. 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. Frequency modulation is widely used for fm radio broadcasting.
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