S. Mandayam/ ECOMMS/ECE Dept./Rowan University Electrical Communications Systems ECE Spring 2009 Shreekanth Mandayam Phil Mease ECE Department Rowan University Lab 2: Pre-lab Instruction

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

S. Mandayam/ ECOMMS/ECE Dept./Rowan UniversityPlan Baseband and Bandpass Signals Modulation Amplitude Modulation AM: Envelope Detector DSB-SC Modulation Systems Signals Complex Envelope Time Domain Spectrum Systems Balanced Modulator Coherent Detector Lab Project 2

S. Mandayam/ ECOMMS/ECE Dept./Rowan UniversityModulation Modulating Signal Message Signal m(t) (Baseband) Modulated Signal s(t) (Bandpass) Information Modulation Frequency Translation What is it? How is it done? Modulator message: m(t) carrier: c(t) s(t): radio signal

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Why Modulate? Antenna size considerations Narrow banding Frequency multiplexing Common processing

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Battle Plan for Analyzing any Comm. Sys. Signals Systems Complex Envelope Time Domain Spectrum Power Performance Transmitters Receivers Standards Modulation Index Efficiency Bandwidth Noise

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Amplitude Modulation (AM) Signals Systems Complex Envelope Time Domain Spectrum Power Performance Transmitters Receivers Standards Modulation Index Efficiency Bandwidth Noise

S. Mandayam/ ECOMMS/ECE Dept./Rowan University 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 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 AM: Envelope Detector ~ v i (t) v o (t) RLRL s(t) Circuit Waveforms C s(t) t

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/spring09/ecomms/ demos/dsbsc.m

S. Mandayam/ ECOMMS/ECE Dept./Rowan University DSB-SC: Balanced Modulator AM A c cos2  f c t m(t) AM -A c cos2  f c t -m(t) 

S. Mandayam/ ECOMMS/ECE Dept./Rowan University DSB-SC: Coherent Detector Product Modulator A o cos2  f c t s(t) Local Oscillator Baseband LPF v(t)

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