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Electrical Communications Systems ECE.09.331 Spring 2011

Electrical Communications Systems ECE.09.331 Spring 2011. Lab 2: Pre-lab Instruction. Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/spring11/ecomms/. ECOMMS: Topics. Plan. Baseband and Bandpass Signals Modulation Amplitude Modulation

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Electrical Communications Systems ECE.09.331 Spring 2011

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  1. Electrical Communications SystemsECE.09.331Spring 2011 Lab 2: Pre-lab Instruction Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/spring11/ecomms/

  2. ECOMMS: Topics

  3. Plan • 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

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

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

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

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

  8. Spectrum of Single Tone AM Instrument Demo Matlab Demo http://engineering.rowan.edu/~shreek/spring11/ecomms/demos/am.m

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

  10. |M(f)| |S(f)| -B 0+B f -fc-B -fc -fc+B 0fc-B fc fc+B f Recall: AM Spectrum Message Spectrum AM Spectrum

  11. + vi(t) - AM: Envelope Detector Circuit + + vo(t) C RL s(t) ~ - - Waveforms s(t) t

  12. |M(f)| -B 0+B Signals Systems Modulation Index Efficiency Bandwidth Noise Performance Transmitters Receivers Standards Time Domain Complex Envelope Spectrum Power DSB-SC Modulation Message Spectrum Matlab Demo http://engineering.rowan.edu/~shreek/spring11/ecomms/demos/dsbsc.m f DSB-SC Spectrum |S(f)| -fc-B -fc -fc+B 0fc-B fc fc+B f

  13. AM -m(t) -Accos2pfct DSB-SC: Balanced Modulator AM Accos2pfct m(t) S

  14. DSB-SC: Coherent Detector Product Modulator Baseband LPF v(t) s(t) Aocos2pfct Local Oscillator

  15. Summary

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