Editing Electromagnetic compatibility (section)

== Design ==
{{unreferenced section|date=June 2023}}
[[file:KNCone TV Station DVBS2 PLUS pci card front 0595 by HDTVTotalDOTcom.jpg|thumb|A [[TV tuner card]] showing many small bypass capacitors and three metal shields: the PCI bracket, the metal box with two coax inputs, and the shield for the [[S-Video]] connector]]

Breaking a coupling path is equally effective at either the start or the end of the path, therefore many aspects of good EMC design practice apply equally to potential sources and to potential victims. A design which easily couples energy to the outside world will equally easily couple energy in and will be susceptible. A single improvement will often reduce both emissions and susceptibility. Grounding and shielding aim to reduce emissions or divert EMI away from the victim by providing an alternative, low-impedance path. Techniques include:

* Grounding or earthing schemes such as ''star earthing'' for audio equipment or ''ground planes'' for RF. The scheme must also satisfy safety regulations.
* [[Electromagnetic shielding|Shielded]] cables, where the signal wires are surrounded by an outer conductive layer that is grounded at one or both ends.
* Shielded housings. A conductive metal housing will act as an interference shield. In order to access the interior, such a housing is typically made in sections (such as a box and lid); an RF gasket may be used at the joints to reduce the amount of interference that leaks through. RF gaskets come in various types. A plain metal gasket may be either braided wire or a flat strip slotted to create many springy "fingers". Where a waterproof seal is required, a flexible [[elastomer]]ic base may be impregnated with chopped metal fibers dispersed into the interior or long metal fibers covering the surface or both.

Other general measures include:

* [[Decoupling (electronics)|Decoupling]] or filtering at critical points such as cable entries and high-speed switches, using [[Choke (electronics)|RF chokes]] and/or [[RC circuit|RC elements]]. A [[line filter]] implements these measures between a device and a line.
* [[Transmission line]] techniques for cables and wiring, such as balanced differential signal and return paths, and impedance matching.
* Avoidance of antenna structures such as loops of circulating current, resonant mechanical structures, unbalanced cable impedances or poorly grounded shielding.
* Eliminating spurious rectifying junctions that can form between metal structures around and near transmitter installations. Such junctions in combination with unintentional antenna structures can radiate harmonics of the transmitter frequency.

[[file:Aaronia Spectrum Analyzer Software.jpg|thumb|Spread spectrum method reduces EMC peaks. Frequency spectrum of the heating up period of a switching power supply which uses the spread spectrum method incl. [[Waterfall plot|waterfall diagram]] over a few minutes]]

Additional measures to reduce emissions include:

* Avoid unnecessary [[switch]]ing operations. Necessary switching should be done as slowly as is technically possible.
* Noisy circuits (e. g. with a lot of switching activity) should be physically separated from the rest of the design.
* High peaks at single frequencies can be avoided by using the [[spread spectrum]] method, in which different parts of the circuit emit at different frequencies.
* [[Harmonic]] wave filters.
* Design for operation at lower signal levels, reducing the energy available for emission.

Additional measures to reduce susceptibility include:

* Fuses, trip switches and circuit breakers.
* Transient absorbers.
* Design for operation at higher signal levels, reducing the relative noise level in comparison.
* Error-correction techniques in digital circuitry. These may be implemented in hardware, software or a combination of both.
* Differential signaling or other common-mode noise techniques for signal routing