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lecture6 - EEE455/591 EEE455/591 Fre ncy and...

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EEE455/591 EEE455/591 Frequency and Phase Modulation Frequency and Phase Modulation FM and PM FM and PM Reading: Textbook Sections 3.3, skip 3.3.2 Reading: Textbook Sections 3.3, skip 3.3.2 Topics: Topics: 1. 1. What is FM and PM? Why? What Applications? What is FM and PM? Why? What Applications? 2. 2. Mathematical Description of PM and FM Mathematical Description of PM and FM 3. 3. SpectrumUsageof FM and PM SpectrumUsageof FM and PM 4. 4. Practical Implementations of FM Practical Implementations of FM
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1. FM and PM: What and Why? AngleModulation: Transmit themessagein: - thefrequency f c of thecarrier (FM), or - thephase θ c of thecarrier (PM) - but not theA c amplitudeof thecarrier (AM)! Useextensively in: - FM radio (e.g. KNIX 102.5MHz) - Audio part of TV broadcasting - First generation analog cellular phones (Narrowband FM) Result: Constant envelopemodulated signal: ) 2 cos( ) ( c c c t f A t u θ π + =
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1. FM and PM: Why? Advantages: Improved noiseimmunity Power efficient when amplifiers operates in saturation Immuneto distortion in amplitude. Disadvantages: Takes morebandwidth than AM Morecomplex transceivers. Frequency Modulation: Themessagemodulates thefrequency of thecarrier: PhaseModulation: Themessagemodulates thephaseof thecarrier. ) 2 cos( ) ( c c c t f A t u θ π + =
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2. Representation of PM and FM in Time Phase Modulation (PM) Frequency Modulation (FM) )) ( 2 cos( ) ( t m k t f A t u p c c + = π ) ) ( 2 cos( ) ( τ τ π d m k t f A t u t f c c - + =
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2. “Instantaneous” Frequency of PM and FM Definition of instantaneous frequency: PM: Maximum phasedeviation FM: Maximum frequency deviation Modulation Index PM: FM: For messagebandwidth W )) ( 2 cos( )) ( cos( ) ( t t f A t
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