Electrical Communications Systems ECE.09.433 Spring 2019 Lecture 3b February 7, 2019 Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/spring19/ecomms/

Plan Amplitude Modulation (AM) DSB-SC Modulation Signals Systems Complex Envelope Time Domain Spectrum Power Performance Transmitters Receivers Standards Modulation Index Efficiency Bandwidth Noise

ECOMMS: Topics

Amplitude Modulation (AM) Signals Systems Complex Envelope Time Domain Spectrum Power Performance Transmitters Receivers Standards Modulation Index Efficiency Bandwidth Noise

AM Spectrum Message Spectrum |M(f)| f AM Spectrum |S(f)| f -B 0 +B -fc-B -fc -fc+B 0 fc-B fc fc+B |S(f)| f

Single Tone AM m(t) m(t) = Amcos(2pfmt) Am t c(t) Ac c(t) = Accos(2pfct) s(t) t Ac Ac[1+Am] s(t) = Ac[1 + Amcos(2pfmt)]cos(2pfct)

Spectrum of Single Tone AM Matlab Demo http://engineering.rowan.edu/~shreek/spring19/ecomms/demos/am.m

Percentage Modulation s(t) Amax = Ac[1+Am] Amin = Ac[1-Am] Ac t

AM Bandwidth Message Spectrum |M(f)| f AM Spectrum |S(f)| f -B 0 +B -fc-B -fc -fc+B 0 fc-B fc fc+B |S(f)| f

AM Power & Efficiency

AM Standards See p. 320

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

DSB-SC Modulation Signals Systems Message Spectrum Matlab Demo Time Domain Complex Envelope Spectrum Power Performance Transmitters Receivers Standards Modulation Index Efficiency Bandwidth Noise Message Spectrum -B 0 +B |M(f)| Matlab Demo http://engineering.rowan.edu/~shreek/spring19/ecomms/demos/dsbsc.m f DSB-SC Spectrum |S(f)| -fc-B -fc -fc+B 0 fc-B fc fc+B f

Summary