1. ANGLE MODULATION AND DEMODULATION
C H A P T E R 5
ANGLE MODULATION AND DEMODULATION
Fundamental of Communication Systems
ELCT332 Fall

2. Concept of instantaneous frequency.
Nonlinear Modulation
Frequency Modulation (FM)
Phase Modulation (PM)
Angle Modulation
Exponential Modulation
Instantaneous Angular Frequency
Phase Modulation
Concept of instantaneous frequency.
Frequency Modulation
Fundamental of Communication Systems
ELCT332 Fall

3. Phase and frequency modulation are equivalent and interchangeable.
Nonlinear Modulator
Phase and frequency modulation are equivalent and interchangeable.
Fundamental of Communication Systems
ELCT332 Fall

4. from the modulated phase through the inverse filter 1/H(s).
Modulation and Demodulation
Generalized phase modulation by means of the filter H(s) and recovery of the message
from the modulated phase through the inverse filter 1/H(s).
Fundamental of Communication Systems
ELCT332 Fall

5. Example
Sketch FM and PM waves for the modulating signal m(t), The constants kf and kp are 2π×105 and 10π, respectively, and the carrier frequency fc is 100MHz.
FM and PM waveforms.
Fundamental of Communication Systems
ELCT332 Fall

6. Example
Sketch FM and PM waves for the modulating signal m(t), The constants kf and kp are 2π×105 and π/2, respectively, and the carrier frequency fc is 100MHz.
Frequency shift keying:
modulating by a digital signal
Phase shift keying
Fundamental of Communication Systems
ELCT332 Fall

7. Bandwidth of Angle Modulated Waves
Narrowband FM (NBFM)
Narrowband PM (NBPM)
Fundamental of Communication Systems
ELCT332 Fall

8. Bandwidth of Angle Modulated Waves: Wideband FM (WBFM)
Peak Frequency Deviation
Fundamental of Communication Systems
ELCT332 Fall

9. Spectral Analysis of Frequency Modulation
Fundamental of Communication Systems
ELCT332 Fall

10. What will be the bandwidth if the amplitudde of m(t) is doubled?
Example: Estimate BFM and BPM for the modulating signal m(t) for kf and kp are 2π×105 and 5π, respectively. Assume the essential bandwidth of the periodic m(t) as the frequency of its third harmonic.
What will be the bandwidth if the amplitudde of m(t) is doubled?
Fundamental of Communication Systems
ELCT332 Fall

11. Narrowband PM generator. (b) Narrowband FM signal generator.
Generating FM Waves: NBFB Generation
Narrowband PM generator. (b) Narrowband FM signal generator.
Fundamental of Communication Systems
ELCT332 Fall

12. Eliminate the amplitude variations of an angle-modulated carrier
Bandpass Limiter
Eliminate the amplitude variations of an angle-modulated carrier
(a) Hard limiter and bandpass filter used to remove amplitude variations in FM wave. (b) Hard limiter input-output characteristic.
(c) Hard limiter input and the corresponding output. (d) Hard limiter output as a function of θ.
Modern Digital and Analog Communication Systems
ELCT332 Fall

13. Block diagram of the Armstrong indirect FM transmitter.
Indirect Method of Armstrong: WBFM Generation
Generating NBFM first and then converted to WBFM by using additional frequency multipliers.
Frequency multiplier can be realized by a nonlinear device followed by a bandpass filter.
Block diagram of the Armstrong indirect FM transmitter.
Fundamentals of Communication Systems
ELCT332 Fall

14. Designing an Armstrong indirect modulator.
Example: Design an Armstrong indirect FM modulator to generate an FM signal with carrier frequency 97.3 MHz and Δf=10.24kHz. A NBFM generator of fc1=20 kHz and Δf=5Hz is available. Only frequency doublers can be used as multipliers. Additionally, a local oscillator with adjustable frequency 400 and 500 kHz is readily available for frequency mixing.
Designing an Armstrong indirect modulator.
Fundamentals of Communication Systems
ELCT332 Fall

15. (c) FM demodulation by direct differentiation.
Demodulation of FM Signals
Slope Detection
(a) FM demodulator frequency response. (b) Output of a differentiator to the input FM wave.
(c) FM demodulation by direct differentiation.
Fundamentals of Communication Systems
ELCT332 Fall

16. Effects of Nonlinear Distortion and Interference
Immunity of Angle Modulation to Nonlinearities
Amplitude Modulation
Fundamentals of Communication Systems
ELCT332 Fall

17. Interference Effect
Angle modulation is also less vulnerable than AM to small signal interference from adjacent channels
Effect of interference in PM, FM, and FM with preemphasis-deemphasis (PDE).
Modern Digital and Analog Communication Systems
Lathi Copyright © 2009 by Oxford University Press, Inc.

18. Figure 5.15 Preemphasis-deemphasis in an FM system.
Modern Digital and Analog Communication Systems
Lathi Copyright © 2009 by Oxford University Press, Inc.

19. Figure 5. 16 (a) Preemphasis filter and (b) its frequency response
Figure 5.16 (a) Preemphasis filter and (b) its frequency response. (c) Deemphasis filter and (d) its frequency response.
Modern Digital and Analog Communication Systems
Lathi Copyright © 2009 by Oxford University Press, Inc.

20. Figure 5.17 Superheterodyne receiver.
Modern Digital and Analog Communication Systems
Lathi Copyright © 2009 by Oxford University Press, Inc.

21. Figure 5. 18 (a) FM stereo transmitter
Figure 5.18 (a) FM stereo transmitter. (b) Spectrum of a baseband stereo signal. (c) FM stereo receiver.
Modern Digital and Analog Communication Systems
Lathi Copyright © 2009 by Oxford University Press, Inc.

22. Figure 5.19
Modern Digital and Analog Communication Systems
Lathi Copyright © 2009 by Oxford University Press, Inc.

23. Figure 5.19 FM and PM signals in the time and frequency domains.
Modern Digital and Analog Communication Systems
Lathi Copyright © 2009 by Oxford University Press, Inc.

24. Figure 5.20 Signals at the demodulator: (a) after differentiator; (b) after rectifier.
Modern Digital and Analog Communication Systems
Lathi Copyright © 2009 by Oxford University Press, Inc.

25. Figure 5.21 FM modulation and demodulation: (a) original message; (b) recovered signal.
Modern Digital and Analog Communication Systems
Lathi Copyright © 2009 by Oxford University Press, Inc.

26. Figure P.5.1-1
Modern Digital and Analog Communication Systems
Lathi Copyright © 2009 by Oxford University Press, Inc.

27. Figure P.5.1-2
Modern Digital and Analog Communication Systems
Lathi Copyright © 2009 by Oxford University Press, Inc.

28. Figure P.5.1-3
Modern Digital and Analog Communication Systems
Lathi Copyright © 2009 by Oxford University Press, Inc.

29. Figure P.5.1-5
Modern Digital and Analog Communication Systems
Lathi Copyright © 2009 by Oxford University Press, Inc.

30. Figure P.5.4-1
Modern Digital and Analog Communication Systems
Lathi Copyright © 2009 by Oxford University Press, Inc.

31. Figure P.5.4-2
Modern Digital and Analog Communication Systems
Lathi Copyright © 2009 by Oxford University Press, Inc.