Amplitude Modulation

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?

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

Spectrum Double Side Band Full Carrier Spectrum LSB, USB, Carrier

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

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

AM Radio Source Carrier Frequency Performance Audio, 20-20 kHz 5 kHz bandwidth 250-500 km range 50 µV sensitivity

AM Radio

Commercial AM Radio Circuit Diagram

Commercial Radio Circuit Board

Block Diagram

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

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

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

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

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

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

Lab and Projects Virtual Laboratory Simple AM Projects Experiments 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

AM Transmitter History Block Diagram Automatic Level Control m < 1

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

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

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

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

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

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

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

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

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

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