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Electro Magnetic Compatibility
The Definition of Electro Magnetic Compatibility:"You can watch "Oprah" with your Television Set sitting on top of a working PC" 
-  Transmission Lines  - PCB Layout  -  PCB Design  - Apertures  - Enclosures  -  Shielding  -  Bypassing  -  Decoupling  -  Ground Planes  -  Near-field/Far-field  -  Reading List  - More Books on EMC
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Words to Live By:
The Dichotomy of EMC:
What is Good Practice for the Circuit isn't necessarily Best for EMC.
What is Good Practice for EMC isn't necessarily Best for the Circuit.
--Good Luck...
Unless or until you Understand ANALOG, You will only solve your EMC Problems by Sheer Luck!
However,
When you thoroughly Understand ANALOG, You will only solve your EMC Problems by Sheer Luck!
One's ability to solve EMC Problems is a little like the Programmer's ability to write "Bug-Free" code: Less than 10% of those who write code, write (near) Bug-Free code; however, 90% of those who write code think they are in that 10%!
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Every Signal Should Have Its 
Own Ground Return ! 
 
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Transmission Lines
Transmission Lines can Radiate:
The Shield of a Coax can Radiate
Be careful of SWR on Coax, it can Radiate if not Terminated correctly, or if there are Discontinuities.

Shielded Twisted Pair is Best...
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Bypass & Decoupling
 "Bypass Anything that Moves" 
Bypass Capacitors are self Resonant
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Voltage Regulators offer the Best Decoupling
    Voltage Regulators Will Generate Parasitic Oscillations if not Bypassed Properly!
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Ground Planes
Every Signal Should Have Its Ground Return
 

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Shielding
Real Shields have No Current flowing thru them: 
They are "Grounded," or Referenced, at only One Point!
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    Enclosures

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    Leakage Apertures
Diffraction: 
Openings or Apertures in Enclosures Appear as Point Sources, and Radiate their Venomous Exhalings.

Area of the Apertures is less important than Length, e.g., Seams and Joints.
They start looking like Slot Antennas. 

Worry if the Length of the opening is greater than  ~ 1/20 Wavelength of the Highest Frequency of interest.

    Some Notorious Apertures I have Known: 
CRTs              Lamps/LEDs
Switches        Connectors
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    Bathroom Material
Noise Reduction Techniques in Electronic Systems, 2nd Ed., H.W. Ott 
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ISBN:

High Speed Digital Design, (The Art of Black Magic),
* * * * *
  ISBN:
More Books on EMC

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  Avoid extraneous currents in the coax shield: maintain shield isolation.
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This is GOOD for the Circuit.  --         This is GOOD for EMC.       --         This is GOOD for Both.
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Currents in either power plane can couple NOISE to the other; the coupling mechanism is mostly magnetic.
 Transmission Line Termination Effects

 

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 Transmission Line Reflections due to improper Termination Impedance 
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In dealing with a Radiation Source--be it an Antenna or a Circuit Board: 

The dominant energy in the Far Field is Electric.
 
 
 

The dominant energy in the Near F ield  is Magnetic. 
  More Books on EMC
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Copyright 1999 Web Author: Glen A. Williamson

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