# ANGLE MODULATION AND DEMODULATION

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

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

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

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

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

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

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

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

Spectral Analysis of Frequency Modulation
Fundamental of Communication Systems ELCT332 Fall

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

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

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

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

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

(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

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

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.

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

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.

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

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.

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

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.

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.

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.

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

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

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

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

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

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