S. Mandayam/ ECOMMS/ECE Dept./Rowan University Electrical Communications Systems Spring 2005 Shreekanth Mandayam ECE Department Rowan University Lecture 4b February 23, 2005

S. Mandayam/ ECOMMS/ECE Dept./Rowan UniversityPlan Amplitude Modulation AM Features AM Modifications DSB-SC Signals Systems Time Domain Complex Envelope Spectrum Power Performance Transmitters Receivers Standards Modulation Index Efficiency Bandwidth Noise

S. Mandayam/ ECOMMS/ECE Dept./Rowan University ECOMMS: Topics

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Recall: AM Spectrum -B 0 +B |M(f)| f -f c -B -f c -f c +B 0 f c -B f c f c +B |S(f)| f Message Spectrum AM Spectrum

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Single Tone AM s(t) = A c [1 + A m cos(2  f m t)]cos(2  f c t) c(t) = A c cos(2  f c t) m(t) = A m cos(2  f m t) t m(t) AmAm t c(t) AcAc s(t) t AcAc A c [1+A m ]

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Spectrum of Single Tone AM Matlab Demo Instrument Demo

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Percentage Modulation s(t) t AcAc A max = A c [1+A m ] A min = A c [1-A m ]

S. Mandayam/ ECOMMS/ECE Dept./Rowan University AM Bandwidth -B 0 +B |M(f)| f -f c -B -f c -f c +B 0 f c -B f c f c +B |S(f)| f Message Spectrum AM Spectrum

S. Mandayam/ ECOMMS/ECE Dept./Rowan University AM Power & Efficiency

S. Mandayam/ ECOMMS/ECE Dept./Rowan University AM Standards See p. 308

S. Mandayam/ ECOMMS/ECE Dept./Rowan University AM: Features AM system is very cheap to build and maintain AM is wasteful of power - max efficiency is 33% AM is wasteful of bandwidth - twice the message bandwidth is required AM Modifications: DSB-SC SSB VSB

S. Mandayam/ ECOMMS/ECE Dept./Rowan University DSB-SC Modulation Signals Systems Time Domain Complex Envelope Spectrum Power Performance Transmitters Receivers Standards Modulation Index Efficiency Bandwidth Noise -B 0 +B |M(f)| f -f c -B -f c -f c +B 0 f c -B f c f c +B |S(f)| f Message Spectrum DSB-SC Spectrum Matlab Demo /~shreek/spring05/ecomms/ demos/dsbsc.m

S. Mandayam/ ECOMMS/ECE Dept./Rowan UniversitySummary