chap5_lec1 - C hapte 5 r AM FM and Digital Modulate S m d...

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Eeng 360 1 Chapter 5 AM, FM, and Digital Modulated Systems Amplitude Modulation (AM) Double Sideband Suppressed carrier (DSSC) Assymetric Sideband Signals Single sideband signals (SSB) Frequency Division Multiplexing (FDM) Huseyin Bilgekul Eeng360 Communication Systems I Department of Electrical and Electronic Engineering Eastern Mediterranean University
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Eeng 360 2 The modulated bandpass signal can be described by ( 29 ( 29 [ ] c c f f G f f G f V - - + - = * 2 1 ) ( ( 29 ( 29 [ ] c g c g v f f P f f P f P - - + - = 4 1 ) ( Bandpass Signaling Review The voltage spectrum of the bandpass signal is The PSD of the bandpass signal is ( 29 ( 29 [ ] ; t g F f G = ( 29 g(t); envelope complex the of PSD - f P g Where } ) ( Re{ ) ( t j C e t g t s ω = Frequency Carier - ; 2 c f f c c π ϖ = Where Modulation Mapping function: Convert m ( t ) → g ( t ) Ref : Table 4-1
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Eeng 360 3 Amplitude Modulation )] ( 1 [ ) ( t m A t g c + = The C omplex Envelope of an AM signal is given by A c indicates the power level of AM and m ( t ) is the Modulating Signal A c [1+ m ( t )] In-phase component x(t) If m ( t ) has a peak positive values of +1 and a peak negative value of -1 AM signal 100% modulated Representation of an AM signal is given by ( ) [1 ( )]cos c c s t A m t t ϖ = + Envelope detection can be used if % modulation is less than 100%.
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Eeng 360 4 An Example of a message signal m ( t ) Waveform for Amplitude modulation of the message signal m ( t ) Amplitude Modulation
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Eeng 360 5 Amplitude Modulation An Example of message energy spectral density. Energy spectrum of the AM modulated message signal. B 2B Carrier component together with the message
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Eeng 360 6 ] 0 [i.e., modulation of absence in the envelope AM of Level - )] ( 1 [ of value Minimum - )] ( 1 [ of value Maximum - min max = + + m(t) A t m A A t m A A c c c Definition: The percentage of positive modulation on an AM signal is [ ] max % Positive Modulation 100 max ( ) 100 c c A A m t A - = × = × [ ] min 100 min ( ) 100 c c A A m t A - × = - × The percentage of negative modulation on an AM signal is [ ] [ ] max min max ( ) min ( ) % Modulation 100 100 2 2 c m t m t A A A - - = × = × The percentage of overall modulation is AM – Percentage Modulation If m ( t ) has a peak positive values of +1 and a peak negative value of -1 AM signal 100% modulated
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Eeng 360 7 AM Signal Waveform A max = 1.5A c A min = 0.5 A c % Positive modulation= 50% % Negative modulation =50% Overall Modulation = 50%
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Eeng 360 8 AM – Percentage Modulation Under modulated (<100%) 100% modulated Envelope D etector Can be used Envelope Detector Gives Distorted signal Over Modulated (>100%)
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This note was uploaded on 05/24/2011 for the course EE 324 taught by Professor Emreaktaş during the Spring '11 term at Hacettepe Üniversitesi.

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chap5_lec1 - C hapte 5 r AM FM and Digital Modulate S m d...

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