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Amplitude Modulation.

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Presentation on theme: "Amplitude Modulation."— Presentation transcript:

1 Amplitude Modulation

2 Basic AM Modulation Amplitude Spectrum Modulation index 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? Efficiency in Using Power?
Two side bands Efficiency in Using Power? Carrier Side band Information in side band Carrier for synchronization

6 Variations of AM Bandwidth Efficiency Power Efficiency Complication
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 Carrier Frequency Performance Audio, 20-20 kHz
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 Autodyne Oscillator and Mixer
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 Local Oscillator Mixer
RF amplifier Bandpass filter Local Oscillator Mixer Nonlinear device or balanced mixer 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 Waveform 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 Simple AM Projects Experiments
(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
Berkeley RLC Pi and T LC Network Calculator Role of Antenna Impedance transformation between circuit and free space

23 Short Wave Radio Terrestrial Coverage, HAM
Regenerative Receiver Project

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

25 AM Stereo Two Channels Quadrature Amplitude Modulation
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 Coherent Detection
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 Numerical Analysis
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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