Technician's EMI Handbook (eBook)

Cover 1
Contents 6
Preface 12
Chapter 1. Introduction to the EMI Problem 14
Chapter 2. Electrical and Electromagnetic Fundamentals 18
What Is Electricity? 18
Positive and Negative Electricity 18
Electronic Model of the Atom 19
The Bohr Model of the Atom 20
Electron Shells 21
Electron Subshells and Electron Spin 22
Electron Valence and Free Electrons 22
Conductors, Insulators, and Semiconductors 23
The Unit of Electric Charge 24
Electrical Polarities 24
Millikan’s Oil Drop Experiment 26
Electrical Potential 26
Electrical Current and Its Units 28
Electrical Current vs Electrical Charge 28
Types of Current Flow 28
Resistance to Electrical Current 29
Conductance 30
Current Flow Direction 30
Electrical Power 31
Electrical Sources 31
The Electromagnetic Field 32
Sources of Electromagnetic Interference 34
Chapter 3. Fundamentals of Electromagnetic Interference 36
Fundamental Causes of EMI 36
The Antenna 37
Modes of Entry 37
Differential-Mode vs Common-Mode Signals 38
Equipment Design Considerations 39
Radio-Frequency Radiation 39
Near Fields and Far Fields 40
Chapter 4. Grounding Methods for RF Systems 42
Schematic Symbols 42
Different Grounds 43
Grounding Systems 46
Ground Designs 47
Other Ground Electrodes 50
Installing Ground Rods 54
Tower Grounding 56
Vertical Antenna Counterpoise Grounds ("Radials") 56
Conclusion 59
Chapter 5. Shielding Electronic Circuits 60
Approaches to Shielding 62
Skin Effect and Skin Depth 63
Ground Planes 64
Shielded Boxes 65
Holes in Shields 66
Double Shielding 68
Multicompartment Shielding 68
Spray-On Shielding 68
Connectors, Meters, and Dials 68
Installing a Coaxial Connector 70
Guard Shielding 71
Grounding and Ground Loops 75
Chapter 6. Filtering Electronic Circuits 78
Shielding 78
Basic Types of Filters 78
Filter Circuits 80
R-C EMI/RFI Protection 82
Feedthrough Capacitors 83
Notch Filtering 85
Twin-Tee Notch Filter Networks 86
Active Twin-Tee Notch Filters 87
Adjustable Bridged-Tee Circuits 89
Gyrator Circuits 90
General Guidelines 91
Conclusion 92
Chapter 7. AC Power-Line and Electrical Device EMI 94
120/240 Volt Electrical System 95
Noise 96
Regulatory/Legal Issues 96
Corona and Spark 97
Safety 98
Locating EMI Sources 98
Filter Solution 98
Electric Motors 99
Common-Mode Filtering 99
Chapter 8. Controlling Transmitter Spurious Emissions 102
Types of Transmitter 102
Operating the Transmitter 106
What to Do? 109
Be Wary! 112
Transmitter Test Setup 112
Third-Harmonic or Higher 113
VHF and Up Transmitters 114
Chapter 9. Telephones and EMI 116
The Federal Communications Commission 116
The Telephone Company 116
The Radio Owner 117
The Telephone Manufacturer 117
The Telephone Owner 117
Technica lIssues 117
Twisted Pair, Flat ( Parallel ) , and Shielded Wiring 118
Common Mode vs Differential Mode 119
Resonances 119
Telephone Ground 119
Corrosion 119
Substandard Wiring 119
Telephone Classification 120
Telephone Registration Numbers 120
Capacitors 120
Common-Mode RF Chokes 120
Filtering 121
Chapter 10. Noise Cancellation Bridges 126
A Simple Bridge Circuit 129
A Different Bridge 132
Conclusion 132
Chapter 11. Locating EMI Sources 134
RF Sleuthing Tools 134
RF Detectors 138
Radio Direction Finding 139
Field Improvisation 143
Regular Loop Antennas 143
Sense Antenna Circuit 144
Switched Pattern RDF Antennas 145
Chapter 12. EMI to Television, Cable TV, and VCR Equipment 148
The Basic Television Receiver 148
Fundamental Overload 150
Harmonic Overload 150
Audio Rectification 150
IMD Interference 150
IF Interference 151
Direct Pickup 151
Common-Mode vs Differential-Mode Signals 151
Common-Mode Filters 151
Filtering 152
Stubs for EMI Elimination 153
Faraday Shielded Coaxial Cable 153
Cable Television Systems 154
Two-Way CATV 155
Channelization 155
Leakage 155
Responsibility 155
Finding Leaks 155
What to Do When the Interference Is at the Subscriber End 156
What to Do When the Customer Is at Fault 156
VCRs 156
Chapter 13. EMI to Consumer Electronics 158
Roles and Responsibilities 158
The Source of the Problem 159
Typical Audio System 159
Pathways for Trouble 160
Troubleshooting 160
Cures 161
Shielding 162
Grounding 162
Chapter 14. EMI from Computers 164
The Law 164
The Problems with Computers 164
Cabinetry 166
Troubleshooting Computer EMI 167
The Role of Ferrite Chokes 167
Ground Loops 168
EMI to Computers 168
Chapter 15. Mystery EMI: Rusty Downspouts and All That 170
Moodie and the Crown Vickie 170
The High Hum Level„FM Broadcasting Station 171
The Slack Coax Caper 171
Lesson Learned: Don't Complain Too Loudly 172
Rusty Downspouts 174
Chapter 16. Radio Receiver Basics 176
Signals, Noise, and Reception 176
Thermal Noise 177
The Reception Problem 178
Strategies 178
Radio Receiver Specifications 179
Origins 179
Superheterodyne Receivers 181
Receiver Performance Factors 185
Units o f Measure 185
Noise 186
Signal-to-Noise Ratio (SNR or Sn) 189
Noise Factor, Noise Figure, and Noise Temperature 189
Noise in Cascade Amplifiers 190
Receiver Noise Floor 191
Static Measures of Receiver Performance 191
Sensitivity 191
Selectivity 195
Stability 199
AGC Range and Threshold 199
Dynamic Performance 200
Intermodulation Products 200
-1 dB Compression Point 201
Third-Order Intercept Point 202
Dynamic Range 204
Blocking 205
Cross-Modulation 205
Reciprocal Mixing 207
IF Notch Rejection 207
Internal Spurii 208
Chapter 17. Dealing with Radio Receiver System EMI 210
Intermod Hill: A Tale of Woe 211
The Problem 212
The Attenuator Solution 215
The Antenna Solution 215
The Filter Solution 216
Transmission Line Stubs 220
Shielding 220
Expected Results 221
Difficult Cases 221
The Solutions 221
Chapter 18. Electrostatic Discharge (ESD) 222
ESD Effects 224
Identification by Class 224
ESD Control Procedures 225
Work Areas 225
Protective Flooring 225
Workbenches 225
Equipment 226
Clothing 226
ESD-Protective Materials 226
Chapter 19. Regulatory Issues 228
Anechoic Chambers and OATS 229
Screened Rooms 231
Appendix A. Automotive Interference Solution 232
ARRL Technical Information Service Information on Automobile–Radio Interference (Both Ways) 232
Automotive Interference Problems: What the Manufacturers Say 232
Wheels Start to Turn 234
ARRL Surveys Auto Manufacturers 234
What the Manufacturers Say 236
By Ed Hare, W1RFI, ARRL Laboratory Supervisor 243
Appendix B. FDA Documents on EMI 248
CDRH Medical Device Electromagnetic Compatibility Program 248
Typical Electromagnetic Environment for Medical Devices 248
CDRH Medical Device Electromagnetic Compatibility Program 248
Medical Devices and EMI: The FDA Perspective 248
The EMI Problem 249
The Complexity of Device EMI 249
FDA Concern with EMI 250
Formation of the CDRH EMC Working Group 250
Plans for Device EMC 251
Research and Standards 252
Work with Other Agencies 252
Some Accomplishments to Date 253
Summary 254
References 254
Electromagnetic Interference (EMI) Testing of Medical Devices 256
New Documents Available to Help Resolve Medical Device EMC Problems 259
Index 262