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Amplitude Modulation. Basic AM Modulation –Amplitude –Spectrum Carrier Sideband –Modulation indexModulation index 0 < m < 1 How to measure? –Modulated.

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Presentation on theme: "Amplitude Modulation. Basic AM Modulation –Amplitude –Spectrum Carrier Sideband –Modulation indexModulation index 0 < m < 1 How to measure? –Modulated."— Presentation transcript:

1 Amplitude Modulation

2 Basic AM Modulation –Amplitude –Spectrum Carrier Sideband –Modulation indexModulation 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, kHz Carrier Frequency –525 – 1705 kHz Performance –5 kHz bandwidth – 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/load Category.dohttp://www.mathworks.com/matlabcentral/fileexchange/load Category.do (Search: FM AM) –Matlab project –Software Radio (http://www.wpi.edu/Pubs/E-project/Available/E- project /unrestricted/DASR_MQP_REPORT.pdf) Simple AM Projects Experiments –Agilent AM modulation –MC1496

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 Amplifier Impedance 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-2005/025E9FB7-46C EA-CBD23EEC9D98/0/lec4.pdfhttp://ocw.mit.edu/NR/rdonlyres/Electrical-Engineering-and- Computer-Science/6-776Spring-2005/025E9FB7-46C EA-CBD23EEC9D98/0/lec4.pdf Berkeley RLC Pi and T LC Network Calculator –http://bwrc.eecs.berkeley.edu/Research/RF/projects/60GHz/matc hing/ImpMatch.htmlhttp://bwrc.eecs.berkeley.edu/Research/RF/projects/60GHz/matc hing/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.htmhttp://www.electronics-tutorials.com/receivers/regen-radio-receiver.htm

24 HAM –Spectral analysis of audio signals –Antenna projects –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 –DetailsDetails –ChipChip

26 Modern Application of AM Advanced Television Systems Committee (ATSC)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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