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Analog Communications

Analog Communications. Dr. M. Venu Gopala Rao A.M.I.E.T.E , M.Tech, Ph.D ( Engg ) Cert. in R.S.T ( City & Guild’s London Institute , London ) F.I.E.T.E, L.M.I.S.T.E, I.S.O.I. , S.S.I. , M.I.A.E . Professor, Dept. of ECE , K L University mvgr03@kluniversity.in. Angle Modulation.

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Analog Communications

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  1. Analog Communications Dr. M. Venu Gopala Rao A.M.I.E.T.E,M.Tech, Ph.D(Engg) Cert. in R.S.T (City & Guild’s London Institute, London) F.I.E.T.E,L.M.I.S.T.E, I.S.O.I., S.S.I., M.I.A.E. Professor,Dept. of ECE, K L University mvgr03@kluniversity.in

  2. Angle Modulation The phase angle of the carrier wave is varied in accordance with the amplitude of modulating signal is referred to as ‘Angle Modulation’. PM: The phase of carrier wave is varied in accordance with the amplitude of message signal. FM: The frequency of the carrier wave is varied in accordance with the amplitude of the modulating signal

  3. Phase angle and Instantaneous Frequency The instantaneous frequency

  4. Phase Modulation

  5. Phase Modulation The phase of carrier wave is varied in accordance with the amplitude of message signal. Assume where is phase modulation sensitivity constant. • Then the resulting Phase Modulated wave is • In this case the instantaneous angular frequency is given by Hence in PM the instantaneous angular frequency varies linearly with the derivative of the modulating signal.

  6. Frequency Modulation

  7. Frequency Modulation The frequency of carrier wave is varied in accordance with the amplitude of message signal. The instantaneous angular frequency is given by or where is frequency modulation sensitivity constant Then the resulting Frequency Modulated wave is

  8. AM, PM and FM Waveforms

  9. PM and FM Waveforms

  10. Relationship between PM and FM • Equations and show that in both PM and FM, the angle of a carrier is varied in proportion to some measure of m(t). • In PM : Directly proportional to m(t) • In FM : Directly proportional to integral of m(t)

  11. Example1

  12. Example 2

  13. Single Tone Angle Modulation (PM) Let a message signal

  14. Single Tone Angle Modulation (FM) For a single tone FM Modulation is given by

  15. Brief Summary

  16. Phase and Frequency Deviation

  17. Phase and Frequency Deviation

  18. Narrowband F.M

  19. Narrowband F.M.

  20. Frequency spectrum of Narrow Band Frequency Modulation The time domain expression for NBFM is The frequency spectrum of Narrow Band Frequency Modulationis represented by

  21. Spectrum of AM and NBFM

  22. Phasor Diagrams

  23. Bandwidth of NBFM The time domain expression for NBFM is It resembles the AM signal and hence bandwidth is twice of the message signal frequency

  24. Narrow Band Angle Modulation for Base Band Signal Let a base-band signal represented by m(t)is band limited to ‘W’ Hz

  25. NBFM for Base Band Signal For and where

  26. NBPM for Base Band Signal , and For

  27. Comparison Similarities: • Both have the same modulated bandwidth 2W, where W is the highest modulating signal frequency. • The sideband spectrum for FMhas a phase shift of900with respect to the carrier, whereas that of AMisin-phasewith thecarrier. Differences: • In an AM signal, the oscillation frequency is constant and the amplitude varies with time, whereas in an FM signal, the amplitudestays constant and frequency varies with time.

  28. END

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