3.AMFMTV - Amplitude Modulation Basic AM Modulation...

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Amplitude Modulation
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Basic AM Modulation Amplitude Spectrum Carrier Sideband Modulation index 0 < m < 1 How to measure? Modulated carrier vs baseband signal What happens when m>1? t E t m t v C C m ϖ cos ) cos 1 ( ) ( + = m C C ±
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Waveforms Base Band and Modulation m = 100% m = 120% Math Real
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Spectrum Double Side Band Full Carrier Spectrum LSB, USB, Carrier
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Efficiency Efficiency in Using Bandwidth? Two side bands Efficiency in Using Power? Carrier Side band Information in side band Carrier for synchronization R E R t E R V P c c c c 2 ) (sin 2 2 2 2 = < = = ϖ 4 2 c usb lsb P m P P = =
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Variations of AM Bandwidth Efficiency Single Side Band Vestigial Side Band Power Efficiency Reduced Carrier Suppressed Carrier Complication Circuits: generation, tuning, detection Filter, tone variation, carrier recovery
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AM Radio Source Audio, 20-20 kHz Carrier Frequency 525 – 1705 kHz Performance 5 kHz bandwidth 250-500 km range 50 μV sensitivity
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AM Radio
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Commercial AM Radio Circuit Diagram
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Commercial Radio Circuit Board
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Block Diagram
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Crucial Components RF Amplifier High dynamic range Autodyne Oscillator and Mixer Tuning Loop Antenna LC resonator Intermediate Frequency Amplifiers 455 kHz Tank circuit (double tuner) with flat center band Diode RF Rectifier Envelope detection Automatic Gain Control Strong vs weak stations Audio Amplifier Speaker
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Heterodyne Incoming RF RF amplifier Bandpass filter Local Oscillator Mixer Nonlinear device or balanced mixer Bandpass filter Signal proportional to local oscillator strength Intermediate Frequency (AM at 455 kHz) No further tuning EMI from Local Oscillator t E t m t v C C m RF ϖ cos ) cos 1 ( ) ( + = t E t v IF C LO LO ) cos( ) ( + = t E E t m t v IF LO C m IF ) cos( ) cos 1 ( ) ( + =
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Detection Baseband Signal Coherent Detection AM modulation Local oscillator Mixer LP filter AC coupling High sensitivity for low S/N t E t A m t v C C RF ϖ cos )) ( 1 ( ) ( + = t E t v C LO LO cos ) ( = t t E E t A m t v C C LO C M cos cos )) ( 1 ( ) ( + = 2 / )) ( 1 ( ) ( LO C LP E E t A m t v + = 2 / ) ( ) ( LO C O E E t A m t v = ) ( ) ( t A m t v RF =
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Envelope Detection Circuit RF rectifier Filter RC time constant Simple for high S/N Waveform
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Detection Square Law Detector Modulation Nonlinearity LF filter Small amplitude and AC coupling t E t A m t v C C RF ϖ cos )) ( 1 ( ) ( + = t E t A m t v C C sq 2 2 2 cos )) ( 1 ( ) ( + = 2 / )) ( 1 ( ) ( 2 2 C LF RF E t A m t v + = - 2 ) ( ) ( C LF E t A m t v =
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This note was uploaded on 02/24/2011 for the course EE 513 taught by Professor Dr.paololiu during the Spring '11 term at SUNY Buffalo.

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3.AMFMTV - Amplitude Modulation Basic AM Modulation...

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