# Ch3(0) - Analog Modulation Analog AM(Amplitude Modulation)...

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Analog Modulation Analog Modulation AM(Amplitude Modulation) Demodulation of AM Signals Angle Modulation

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Why modulate ? Why modulate ? Ease of radiation The size of antenna λ /4 = c/4f If we wish to throw a piece of paper(baseband signal), it cannot go too far by itself. But by wrapping it around a stone(carrier), it can be thrown over a longer distance Simultaneous transmission of several signals FDM(Frequency Division Modulation) Reduce the influence of interference Frequency Hopping Effecting the exchange of SNR with B Shannon’s equation : C is rate of information change per second (bit/s) 2 log (1 ) C B SNR = +
Properties of analog modulation Properties of analog modulation Time domain representation of the modulated signal Frequency domain representation of the modulated signal Bandwidth of the modulated signal Power component of the modulated signal SNR after demodulation Modulator Message Signal (or modulating Signal) Modulated Signal

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AM (Amplitude modulation) AM (Amplitude modulation) Also known as “Linear modulation) Small bandwidth, Power inefficient Applications AM radio, TV video broadcasting(VSB), Point-to-point communications(SSB), Transmission of many telephone channels over microwave links Class of AM DSB-AM(Double Side Band – AM) BW = 2W = 2 * BW of the message signal SSB-AM(Single Side Band – AM) BW = W VSB-AM(Vestigial Side Band – AM) BW = W ~ 2W
DSB – AM DSB – AM Amplitude of modulated signal is proportional to the message signal ( ) cos(2 ) c c c t A f t π = ( ) ( )cos(2 ) c c u t A m t f t = ( ) m t

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DSB-AM at frequency domain DSB-AM at frequency domain Take FT Transmission Bandwidth: B T B T = 2W ( ) [ ( )cos(2 )] ( ) ( ) 2 2 c c c c c c A A U f F A m t f t M f f M f f π = = - + + -W   0   W f M(f) f U(f) f c -f c 2W DSB-AM A AAc 2 /2
Power of modulated signal Power of modulated signal If m(t) is lowpass signal with frequency contents much less than 2f c / 2 / 2 2 2 2 2 / 2 / 2 / 2 2 2 / 2 2 / 2 / 2 2 2 / 2 / 2 2 1 1 lim ( ) lim ( )cos (2 ) 1 cos(4 ) 1 lim ( ) 2 1 1 {lim ( )

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## This note was uploaded on 01/20/2012 for the course EE 301 taught by Professor Ahmetçakar during the Spring '11 term at Gazi Üniversitesi.

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Ch3(0) - Analog Modulation Analog AM(Amplitude Modulation)...

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