1 / 29

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.

micol
Download Presentation

Amplitude Modulation

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related