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Amplitude Modulation

Amplitude Modulation. Basic AM. Modulation Amplitude Spectrum Carrier Sideband Modulation index 0 < m < 1 How to measure? Modulated carrier vs baseband signal What happens when m>1?. Waveforms. Base Band and Modulation m = 100% m = 120% Math Real. Spectrum.

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Amplitude Modulation

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  1. Amplitude Modulation

  2. Basic AM • Modulation • Amplitude • Spectrum • Carrier • Sideband • Modulation index • 0 < m < 1 • How to measure? • Modulated carrier vs baseband signal • What happens when m>1?

  3. Waveforms • Base Band and Modulation • m = 100% • m = 120% • Math • Real

  4. Spectrum • Double Side Band Full Carrier • Spectrum • LSB, USB, Carrier

  5. Efficiency • Efficiency in Using Bandwidth? • Two side bands • Efficiency in Using Power? • Carrier • Side band • Information in side band • Carrier for synchronization

  6. Variations of AM • Bandwidth Efficiency • Single Side Band • Vestigial Side Band • Power Efficiency • Reduced Carrier • Suppressed Carrier • Complication • Circuits: generation, tuning, detection • Filter, tone variation, carrier recovery

  7. AM Radio • Source • Audio, 20-20 kHz • Carrier Frequency • 525 – 1705 kHz • Performance • 5 kHz bandwidth • 250-500 km range • 50 µV sensitivity

  8. AM Radio

  9. Commercial AM Radio • Circuit Diagram

  10. Commercial Radio • Circuit Board

  11. Block Diagram

  12. Crucial Components • RF Amplifier • High dynamic range • Autodyne Oscillator and Mixer • Tuning • Loop Antenna • LC resonator • Intermediate Frequency Amplifiers • 455 kHz • Tank circuit (double tuner) with flat center band • Diode RF Rectifier • Envelope detection • Automatic Gain Control • Strong vs weak stations • Audio Amplifier • Speaker

  13. Heterodyne • Incoming RF • RF amplifier • Bandpass filter • Local Oscillator • Mixer • Nonlinear device or balanced mixer • Bandpass filter • Signal proportional to local oscillator strength • Intermediate Frequency (AM at 455 kHz) • No further tuning • EMI from Local Oscillator

  14. Detection • Baseband Signal • Coherent Detection • AM modulation • Local oscillator • Mixer • LP filter • AC coupling • High sensitivity for low S/N

  15. Envelope Detection • Circuit • RF rectifier • Filter • RC time constant • Simple for high S/N • Waveform

  16. Detection • Square Law Detector • Modulation • Nonlinearity • RF filter • Low pass and AC coupling

  17. Performance • Sensitivity • Fidelity or Bandwidth • Dynamic Range • Selectivity • Adjacent channel • Image Rejection • IF • Spurious Response • Harmonics • Squelch • Noises • Static noise from transmission media • Motor boating noise from drift in frequency

  18. Lab and Projects • Virtual Laboratory • http://www.mathworks.com/matlabcentral/fileexchange/loadCategory.do (Search: FM AM) • Matlab project • http://www.cse.ucsc.edu/classes/ee151/Winter01/ • Software Radio (http://www.wpi.edu/Pubs/E-project/Available/E-project-042805-113037/unrestricted/DASR_MQP_REPORT.pdf) • Simple AM Projects • Experiments • Agilent 33120 AM modulation • MC1496 http://www.onsemi.com/pub/Collateral/AN531-D.PDF

  19. AM Transmitter • History • Block Diagram • Automatic Level Control • m < 1

  20. AM Modulator • Balanced Mixer • Other Circuit • Base band signal modulates oscillator current

  21. Power AmplifierImpedance Matching • Maximize Power to the Load • Impedance • Z = V / I • Change V – I Relation • Transformer • High current, low voltage • Low current, high voltage • RLC Networks • Frequency dependent impedance

  22. Impedance Matching • MIT Open Courseware • http://ocw.mit.edu/NR/rdonlyres/Electrical-Engineering-and-Computer-Science/6-776Spring-2005/025E9FB7-46C3-4718-98EA-CBD23EEC9D98/0/lec4.pdf • Berkeley RLC Pi and T LC Network Calculator • http://bwrc.eecs.berkeley.edu/Research/RF/projects/60GHz/matching/ImpMatch.html • Role of Antenna • Impedance transformation between circuit and free space

  23. Short Wave Radio • Terrestrial Coverage, HAM • http://n5xu.ece.utexas.edu/hamradio/ • Regenerative Receiver Project • http://www.electronics-tutorials.com/receivers/regen-radio-receiver.htm

  24. HAM • http://www.arrl.org/hamradio.html • http://www.qsl.net/dl4yhf/ • Spectral analysis of audio signals • http://www.ac6v.com/ • Antenna projects • http://www.radio.org/linux/ • Linux HAM

  25. AM Stereo • Two Channels • L+R • L-R • Quadrature Amplitude Modulation • Sin, Cos: orthogonal • Increase Information Capacity Without Increasing Bandwidth • Motorola CQUAM System • Details • Chip

  26. Modern Application of AM • Advanced Television Systems Committee (ATSC) • 8-VSB Digital Signaling

  27. AM Noise Analysis • DSBFC Signal and Noise • Baseband signal power: • Carrier power: • Noise spectral density: • Double sideband bandwidth: • Total noise power: • Coherent Detection • In phase noise only • S/N

  28. AM Noise Analysis • Envelope Detection • Signal Dominant Regime • Similar to coherent detection • Noise Dominant Regime • Noise large • Signal small with random phase • Numerical Analysis

  29. AM Review • AM Waveform • Modulation Index Limit • Double Sideband, Full Carrier • Detection Circuits • Coherent detection • Envelope detection • Variations • SSB, RC or SC • Vestigial sideband • AM Transmitter • Impedance matching • Efficiency

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