Effect of frequency mismatch of course, no one is interested in making frequency mismatch intentionally. A phaselocked loop pll can be used to create a complex but highperformance circuit for fm demodulation. Pdf amplitude modulation songkolon samanta academia. Amplitude modulated signal can be represented by the following equation. One approach to reduce this interference, known as. The student will learn the basic concepts of ssb modulation and using the theoretical knowledge of. When transmitted over a linear, timeinvariant lti channel, and if noise is negligible, each sinusoid shows up at the receiver as a sinusoid of the same frequency, as we saw in chapter 12. The functional diagram of the ic is added here again for calculate the.
Envelope intelligence amplitude varies at the beat difference frequency of 1,000 hertz 501,000. It is relatively difficult to tune, as tuned circuit must be tuned to different frequency than carrier frequency. Fsk frequency shift keying d1 63 fsk in f 1 f 2 decision out figure 4. Sc modulation, and demodulation techniques for analog communication. Each channel sharing scheme a set of basis vectors. Spectrum of a dsbscam signal the fourier transform of st is s. In the laboratory, you will use function generator as vco. A demodulation method called coherent demodulation will be explored in this experiment. The carrier frequency 400hz, message signal frequency 10hz, and frequency deviation 100hz. Once a signal has been modulated, information is retrieved through a demodulation process. Mar, 2018 in this video, frequency modulation and demodulation experiment is fully explained and described and is done in fm trainer kit scientech st 2203 kit where output signals are observed in nb202c dso. Demodulation is extracting the original informationbearing signal from a carrier wave. Experiment 5 frequency modulation 1 objective to understand the principles of frequency modulation and demodulation. Adjustments for amplitude and frequency are provided in panel for ease of operation.
A pll can lock onto the frequency of an incoming waveform. Practical of frequency modulator and demodulator youtube. Nov 21, 2017 frequency modulation and demodulation experiment tutorial by mr. Its main advantage is that it is more resistant to additive noise than am. The negative half cycles of the mixed frequency are rectified, as shown in view d. To study amplitude demodulation by linear diode detector 3. T2 use the frequency counter to set the audio oscillator to about 1 khz.
In this experiment, a carrier signal and an audio modulating signal are applied to the modulator ic mc 1496 and the produced modulated waveform is observed. It does not carry much information that we can relate to data or speech. It would be advantageous to have completed some of the part 1 experiments involving linear modulation and demodulation. Exercise 51 generating ssb signals by the filter method 91. When the pll is unlocked condition, if the frequency of the input signal f i will come near to f 0. This demodulator is more complex than most asynchronous demodulators. It is also possible to change the frequency of a signal to give frequency modulation or fm. Frequency modulation consists of encoding information onto a carrier signal by varying the frequency of the carrier. Once the signal has been received, filtered and amplified, it is necessary to recover the original modulation from the carrier.
In this experiment, we will use a famous chip, the lm 566c to generate the fm signal. To study and perform frequency shift keying modulation and demodulation. The coupling and emitter bypass capacitors are chosen as. Prof mist mist, hyderabad ece department page 8 physitechs modulation and demodulation trainer has a carrier generator, which generates carrier wave of 100khz when the trainer is switched on. Tv signal, over an analog bandpass channel at a different frequency, for example over a limited radio frequency band or a cable tv network channel. Experiment 2 experiment 6 experiment dsb sc modulation. Amplitude modulation you will use the ca3080 transconductance amplifier as an amplitude modulator.
Way more information than you ever wanted on how to fell a tree. Frequency modulation fm is a form of modulation in which changes in the carrier wave frequency correspond directly to changes in the baseband signal. The spectra of tonemodulated fm signals are analyzed as well. Cme312 lab manual dsbsc modulation and demodulation experiment 6 experiment 2 part iv.
You are free to choose the frequency and magnitude of the carrier and message signals. Another pitfall of this technique is that it does not have any rejection of unwanted am signals noise. Frequency modulation is widely used on frequencies above 30 mhz, and it is particularly well known for its use for vhf fm broadcasting. Abstract the aim of this paper is to practice the experiments with true mathematical modeling hardware, designed specifically for implementing various communication theories. The demodulated signal spectrum is called the demodulation spectrum see figure 9. Practical approach to frequency modulation and demodulation. Understanding quadrature demodulation radio frequency. Frequency modulation fm is a process in which the carrier frequency is varied by the amplitude of the modulating signal i.
In linear modulation, the amplitude of the transmitted signal varies linearly with the modulating digital signal, mt. Department of electronics and communication engineering. The goal of this experiment is to become familiar with fm modulation and demodulation. Frequency modulation fm is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. A vibration with period t2 or a frequency of 1t2 can be seen, which is known as the carrier frequency. Frequency demodulator, also called frequency splitter, is a circuit that converts momentary frequency changes into linear voltage changes. Upon completion of the experiment, the student will. Here the minimum frequency fmin is assumed to be 5 khz and the maximum frequency fmax is assumed to be 10 khz. In this video, frequency modulation and demodulation experiment is fully explained and described and is done in fm trainer kit scientech st 2203 kit where output signals are observed in. Observe on the variation of am demodulator by changing the amplitude and frequency of audio signal. There will be a minimum frequency separation required of the two tones. These sidebands are visible in the fft as a 1t1 frequency shift in either direction along the frequency axis.
Chapter 6 doublesideband suppressedcarrier amplitude. It reacts to all amplitude changes needs a limiter. Experiments in this lab we will study a few modulation and demodulation circuits. The term and technology is 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. Fm is considered an analog form of modulation because the baseband signal is typically an analog waveform without discrete, digital values.
The vcg input of the wavetek is used as a frequency modulator in part 2c, and the 565 pll is used for fm demodulation in part 2d. Frequency modulation and frequency demodulation experiment. Audio frequency af frequencies that a person can hear. List of experiments sl no experiments page no 1 am modulator and demodulator. To study frequency modulation and determine its modulation factor 4. It is inefficient, as it is linear in very limited frequency range. In the simulation experiment section2, we used the vco to demodulate the information signal to make life easier. To study sampling and reconstruction of pulse amplitude modulation system 6. The 3080 will be used as an amplitude modulator in part 2a. Frequency discrimination slope detector major limitations.
Since the original pulse frequency is around 7 khz the hef4046 ic based demodulator can be designed to receives pulses in the frequency range of 2 to 12 khz. Shashi heres a video i recorded of our lab expert performing frequency modulation and frequency demodulation experiment. The amplitude modulation shows as sidebands of the carrier frequency. Carrier signal a single, high frequency signal that can be modulated. Experiment 2 experiment 6 experiment dsb sc modulation and. The concepts of amplitude modulation, modulation and demodulation, along with their. A carrier wave is purely made up of constant frequency, slightly similar to a sine wave. Radio frequency rf the transmission frequency of electromagnetic radio signals. The frequency modulator and demodulator structures are as explained below. This type of demodulation is therefore called coherent demodulation or detection.
Therefore, an fm demodulator should produce an output which is proportional to this instantaneous frequency. The simplicity of the modulation process contrasted with the strict requirement for a synchronous local carrier at the receiver. The message is recovered as the control input of the vco 4. At least 7 experiments should be performed from the above list. In frequency modulation, the amplitude of the carrier wave is kept constant but its frequency is varied in accordance with the amplitude of the audio frequency signal. In this experiment, we will consider a simple slope detector circuit for fm demodulation.
But quadrature amplitude demodulation can capture the frequency encoded informationthis is simply the rather interesting nature of iq signals. Introduction in chapters 1 and 2 you studied how to apply intelligence modulation to an rfcarrier wave. Therefore, this technique is valid only for a small frequency deviation from the center frequency e. Fm demodulator circuits are found in any receiver that uses fm. In this experiment you will demodulate the fm signal using either slope detector or phase locked loop pll. Eed314 analog communication 20 spring experiment 4 group no grade student number and name student number and name student number and name experiment4 frequency demodulator preliminary work 1.
In experiment 3, dsb signals were generated by the multiplication of a message signal with a carrier waveform. This resulted in the translation of the message spectrum to the carrier frequency location. In any radio that is designed to receive frequency modulated signals there is some form of fm demodulator or detector. Fm demodulation is a key process in the reception of a frequency modulated signal. The frequency of a radiofrequency channel can be explained best as the frequency of a carrier wave. First, since fm only changes the frequency and not the amplitude of the carrier w ave, fm receivers can be built to ignore amplitude voltage changes.
Low frequency signal of approximately 5khz is generated using opamp based wein bridge oscillator. Generation and demodulation of a binary fsk signal. What is fm, frequency modulation electronics notes. To study amplitude demodulation by linear diode detector. Frequency modulation and demodulation experiment youtube. In summary, we can see in two different places and in two different ways the effects of. Let j1 be short circuit and j2 be open circuit to produce the modulated am. In singlechannel efield sensing, the carrier we transmit is m, the sensed value is a, and the noise is n vectors.
Frequency modulation, or fm, is an important method of impressing information on a carrier. Amplitude modulation the voltage dac vdac provides offset to the message signal mt. Hapter modulation and demodulation mit opencourseware. Both modulation and demodulation schemes will be discussed binary fsk.
Rf frequencies are from about 300 khz to the 1,000,000 khz range. While changing the amplitude of a radio signal is the most obvious method to modulate it, it is by no means the only way. Let j1 be short circuit and j2 be open circuit to produce the modulated am signal as the signal source in this experiment. A transistor amplifier is used for additional gain. To study frequency modulation and determine its modulation factor. The receiver must generate a carrier frequency in phase and frequency synchronization with the incoming carrier. It is this process that is called demodulation or detection. Frequency modulation in this experiment, the generation of frequency modulated signals by the direct method and the demodulation of the message signal using a phaselock loop circuit are considered. In this experiment we will introduce the operations of pll frequency demodulator and fm to am conversion discriminator. Signals and demodulation frequency shift keying fsk is the most common form of digital modulation in the high frequency radio spectrum, and has important applications in telephone circuits. Describe fm demodulation circuit operation for the phaseshift and gatedbeam discriminators and the ratiodetector demodulator. Modulation allows us to transmit multiple signals in the same medium i. This article provides a general tutorial on fsk in its many forms. The bandwidth of each is dependent on the message bit rate.
Describe phase demodulation circuit operation for the peak, lowpass filter, and conversion detectors. Use the signal generator to generate an fm signal with the message signal being sine signal. We know that the instantaneous frequency of an fm signal is proportional to the amplitude of the modulating signal. Connect to the two oscilloscope channels using the scope selector, as shown. To perform the frequency modulation and demodulation using fm kit. Frequency division multiplexing, fdma amplitude modulation and demodulation. Analog communication lab manual, prepared by nakka. Demodulation of dsbsc the modulator circuits can be used for demodulation, but replacing the bpf by a lpf of bandwidth b hz. T1 first patch up according to figure 6, but omit the input x and y connections to the multiplier. At least 10 experiments are to performed by students in the semester.
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