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- 1. FREQUENCY<br />MODULATION<br />IN<br />DATA TRANSMISSION<br />
- 2. PRESENTED ON THE BASIS OF TECHNICAL REPORT BY :<br />RAJIB MODAK<br />BISWAJIT MONDAL<br />&<br />PRANAB KUMAR BANDYOPADHYAY<br />
- 3. What is FREQUENCY ??<br />What is MODULATION ??<br /> What is DATA ??<br />What is TRANSMISSION ??<br />
- 4. Modulation<br />Pulse Wave Modulation<br />Continuous Wave Modulation<br />Amplitude Modulation<br />Linear Modulation<br />Non-linear Modulation<br />Frequency Modulation<br />Phase Modulation<br />
- 5. What is Frequency<br /> Modulation ??<br />Carrier Signal <br />Baseband Signal<br />Modulated Signal<br />
- 6. There is two types of Frequency Modulation with respect to bandwidth:---<br />i> Wide Band Frequency Modulation<br />ii> Narrow Band Frequency Modulation<br />
- 7. GENARATION OF NARROW-BAND FM SIGNAL :<br />e<br />(t)<br />_<br />NBFM<br />Integrator<br />m<br />Product Modulator<br />∑<br />+<br />Accos(2Πfct)<br />Phase Shifter<br />Narrow – Band Phase Modulator<br />
- 8. Bandwidth Of FM:<br />Theoretically the Bandwidth Of FM is infinite (for Sinusoidal Modulation). But practically FM wave is effectively limited to a number of significant side frequencies (almost 200 kHz). <br />From Carson’s rule approximation Bandwidth of FM - -<br />BT<br />2<br />f<br />+<br />2fm<br />=<br />BT<br />2<br />f<br />(1 + 1/β)<br />=<br />
- 9.
- 10. Difference Between AM & FM :<br />1><br />In case of AM instantaneous phase contains baseband<br />Signal. But in case of FM that contains baseband as well<br />as higher order odd harmonics.<br />AM signal is amplitude modulated , but FM is amplitude<br />As well as frequency modulated. <br />2><br />3><br />The bandwidth of FM wave is much larger than AM wave.<br />
- 11. How we create FM Signal ?<br />i>Indirect Method<br />ii>Direct Method<br />
- 12. Indirect Method of FM Generation :-----<br />Integrator<br />Narrowband Phase Modulator<br />Frequency<br />Multiplier<br />Base Band Signal<br />FM Signal<br />Crystal Oscillator<br />
- 13. Indirect Method to Generate WBFM for Practical use:-<br />Integrator<br />Narrow<br />Band Phase Modulator<br />Frequency <br />Multiplier<br />(*100)<br />Frequency <br />Multiplier<br />(*75)<br />Mixer<br />FM <br />signal<br />Baseband<br />signal<br />fc=100MHz<br />Δf=75KHz<br />f1 =0.1 MHz<br />f2 =8.5 MHz<br />Crystal Oscillator<br />Crystal Oscillator<br />
- 14. DirectMethod of FM generation:----<br />VCO<br />Frequency Multiplier<br />Mixer<br />Frequency Multiplier<br />Bandpass Filter<br />WBFM<br />Base band<br /> Signal<br />Fixed Oscillator<br />DISADVANTAGE: very poor frequency stability due to unstable basic oscillator unlike crystal oscillator.<br />
- 15. Feedback Scheme For Frequency Stabilization of a Direct Frequency Modulator:- <br />VCO<br />Base Band Signal<br />Frequency stabilized FM wave<br />LPF & Amplifier<br />Frequency Discriminator<br />Mixer<br />Crystal Oscillator<br />
- 16. Demodulation of Frequency Modulated Wave:-<br />Frequency Demodulation is the process that enables us to extract the original modulating signal.<br />There are two basic methods for demodulating the FM waves:<br />Based on Frequency Discrimination <br />Based on Phase Locked Loop<br />
- 17. Frequency discriminator:-<br />A frequency discriminator is an FM demodulator which must produce an output voltage linearly dependent on input frequency.<br />
- 18. Frequency Discrimination(Slope Detection) technique: <br />H(f)<br />Envelope Detector<br />sc(t)<br />sd(t)<br />s(t)<br />t<br />t<br />Sc(t)<br />S(t)<br />Sd(t)<br />t<br />
- 19. Problems:-<br />1>The detector also responds to spurious amplitude variation of the input FM.<br />2> The range of linear slope is quite small.<br />|H(f)|<br />f<br /> f0fc<br />
- 20. Frequency Demodulation using Phase Locked Loop:-<br />PLL is useful in FM demodulation in presence of large noise and low signal power. Thus it finds application in space vehicle to earth data links.<br />Recently it is being used in Commercial FM receiver.<br />
- 21. Phase Locked Loop:-<br />A PLL is basically a negative feedback system. It consists of three major components:<br />A multiplier<br />A loop filter<br />A voltage controlled oscillator(VCO)<br />These are connected together in the form of a feedback loop. <br />Loop Filter<br />X<br /> FM wave<br /> s(t)<br />e(t)<br />v(t)<br />r(t)<br />VCO<br />
- 22. Circuit for Direct FM generation:-<br />FM<br />OSCILLATOR<br />Sound Wave<br />L<br />C<br />Condenser Microphone<br />
- 23. Varactor Diode Modulator:-<br />-Vcc<br />Cc<br />em(t)<br />FM<br />L<br />C<br />Varactor Diode<br />
- 24. Practical Reactance Modulator:-<br />+Vcc<br />RFC<br />R1<br />RFC<br />R1<br />Oscilator<br />Reactance Modulator<br />C<br />FM output<br />C1<br />R2<br />R<br />RE<br />CC<br />RE<br />CE<br />C2<br />C<br />CE<br />R2<br />CB<br />Modulating signal<br />
- 25. FM Receiving System:-<br />Frequency changer circuit<br />
- 26. FM receiver circuit:-<br />The application circuit to generate FM(88-108 MHz) with stereo headphone amplifier<br />
- 27. The<br />Stereo<br />FM<br />
- 28. What Stereo Means :-<br />
- 29. How then comes the virtualization ??<br />
- 30. What do we need for the transmission?<br /><ul><li> We need two different signals L(left) & R(right) to be modulated, transmitted, received and demodulated duly without getting distorted</li></li></ul><li>
- 31. We need :----<br />An input signal<br />Two preemphasizers<br />A DSB-SC modulator<br />A frequency doubler<br />A pilot signal<br />A summer<br />An FM modulator<br />
- 32.
- 33.
- 34. Why do we need L + R & L – R??<br />Compatibility issue<br />A mono phonic receiver will work with only the L+R component and there will no loss of AUDIO(so the signal will have the backward compatibility)<br />
- 35.
- 36. We need :----<br />An input signal (through a LIMITER DISCRIMINATOR)<br />A Low Pass Filter(0-15 KHz)<br />A Bandpass Filter(19 KHz)<br />A Bandpass Filter( 23 – 53 KHz)<br />A pilot signal<br />A Frequency Doubler<br />A Synchronous Detector<br />Two Deephasizers<br />
- 37.
- 38. What is a Limiter<br /> discriminator ??<br />
- 39. What is a <br />preemphasizer ??<br />
- 40. Preemphasizer refers to a system process designed to increase, within a band of frequencies, the magnitude of some (usually higher) frequencies with respect to the magnitude of other (usually lower) frequencies in order to improve the overall signal-to-noise ratio by minimizing the adverse effects of such phenomena as attenuation distortion or saturation of recording media in subsequent parts of the system.<br />
- 41.
- 42.
- 43. A preemphasizer Network<br />
- 44. What is a <br />deemphasizer ??<br />
- 45. Deemphasizer refers to a system process designed to decrease, within a band of frequencies, the magnitude of some (usually higher) frequencies with respect to the magnitude of other (usually lower) frequencies in order to improve the overall signal-to-noise ratio by minimizing the adverse effects of such phenomena as attenuation distortion or saturation of recording media in subsequent parts of the system.<br />
- 46.
- 47.
- 48. A Deemphasizer Network<br />
- 49. QUESTIONS ARE WELCOME<br />

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