Electrical Communications Systems ECE.09.433 Amplitude Modulation I Dr. Shreek Mandayam Electrical & Computer Engineering Rowan University

Plan Baseband and Bandpass Signals Modulation Battle Plan for Analyzing Comm Systems Amplitude Modulation (AM) Time Domain Spectrum

ECOMMS: Topics

Baseband and Bandpass Signals Baseband signals: spectral magnitude is non-zero only near the origin and is zero (or negligible) elsewhere Bandpass signals: spectral magnitude is non-zero only near the vicinity of f = ± fc, were fc >> 0 - fm 0 +fm W(f) f - fc 0 +fc W(f) f Carrier Frequency AF Signals RF Signals

Modulation What is it? How is it done? Modulator Information Modulating Signal Message Signal m(t) (Baseband) Modulated Signal s(t) (Bandpass) Information Modulation Frequency Translation How is it done? Modulator message: m(t) carrier: c(t) s(t): radio signal

Why Modulate? Antenna size considerations Narrow banding Frequency multiplexing Common processing

Battle Plan for Analyzing any Comm. Sys. Signals Systems Complex Envelope Time Domain Spectrum Power Performance Transmitters Receivers Standards Modulation Index Efficiency Bandwidth Noise

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

Summary