apece-302: radio & television...
TRANSCRIPT
APECE-302: Radio & Television Engineering
Course Teacher: S.M. Riazul Islam, PhD
Date: 2013 Year, 07 Month, 02 Day
University of Dhaka, APECELecture Materials on APECE-302
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Applied Physics, Electronics & Communication Engineering
University of Dhaka |APECE
DU
LEC PPT # 03Modulation Techniques
(Part 1)
Contents
Introduction to Modulation What, why and how!
Analog Modulation/Demodulation: AM, FM, and PM DSBSC, SSB, VSB
Superheterodyne Receiver
Digital Modulation/Demodulation: ASK/PSK/FSK/QAM/MSK/M-Ary
Spread Spectrum Modulation: FHSS, DSSS
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University of Dhaka, APECELecture Materials on APECE-302
Introduction
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University of Dhaka, APECELecture Materials on APECE-302
Information-bearing signals from Tx to Rx
Baseband signals
Modulating and modulated signal
Demodulation
Reasons Spectrum management
Different Stations locating
Antenna Height
Introduction
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University of Dhaka, APECELecture Materials on APECE-302
Introduction
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University of Dhaka, APECELecture Materials on APECE-302
Continuous Modulation:Amplitude and Angle
Example: Amplitude andfrequency modulation atRHS
AM
FM
Amplitude Modulation
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University of Dhaka, APECELecture Materials on APECE-302
Amplitude sensitivity; ?unit
Conditions for AM
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University of Dhaka, APECELecture Materials on APECE-302
Spectrum Analysis in AM
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University of Dhaka, APECELecture Materials on APECE-302
Spectrum Analysis of AM
Realization of negative frequency!
Must not be overlapped in LSB and USB
Tx BW is twice the message BW
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University of Dhaka, APECELecture Materials on APECE-302
Virtues and Limitations of AM
Oldest method and simplicity of implementation
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Virtues and Limitations of AM
Wasteful of power
Wasteful of BW
Overcome: DSB-SC, SSB w. system complexity
?Trade-off>>Linear modulation!
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University of Dhaka, APECELecture Materials on APECE-302
Single-tone Modulation
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Modulation Factor
Single-tone Modulation
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Single-tone Modulation
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Single-tone Modulation
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• ??>> Ratio of total side-band power to the total power in the modulated wave
– ??For 100% modulation
Switching Modulator
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Switching Modulator
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Envelope Detector
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Envelope Detector
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Envelope Detector
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DSB-SC Modulation
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DSB-SC Modulation
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Coherent Detection
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Coherent Detection
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• Cut-off frequency > W but less than 2fc-W
• Quadrature null effect of coherent detector? >> perfect Synch.
Angle Modulation
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PM
FM
UM
Angle Modulation
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Angle Modulation
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Frequency Modulation
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Spectral Analysis: Difficult compared to simple AM
Frequency deviation
Proportional to amplitude of m(t) and independent of f_m
Frequency Modulation
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Modulation index
Phase deviation
NB or WB
Frequency Modulation
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NB Frequency Modulation
Frequency Modulation
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Modulation index < 0.3 rad
Frequency Modulation
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University of Dhaka, APECELecture Materials on APECE-302
Difference is algebraic sign of LSB is reversed, so the Tx BW is the same as that if AM (2fm)
Demodulation of FM Signals
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Using Frequency Discriminator Slope Circuit followed by Envelope detector
Demodulation of FM Signals
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University of Dhaka, APECELecture Materials on APECE-302
Demodulation of FM Signals
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Balanced Frequency Discriminator
FM Stereo Multiplexing
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FM Stereo Multiplexing
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Superheterodyne Receiver
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Disadvantage: Image Frequency
Q & A
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