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 Bonding reduces electrostatic EMI by preventing the build-up and subsequent discharge of static charges. Bonding prevents surfaces from electrically resonating and radiating EMI. Bonding eliminates harmonic EMI by eliminating current rectification at contact surfaces. Bonding assures that all parts are at the same potential which prevents higher RF current flow in one part of the structure than another. All RF generators should have a low-impedance path to ground; bonding assures this.

 The engine should have a good ground to the engine mount. Sometimes an aluminum clamp is used around the engine mount. This makes a poor RF ground. The dissimilar metals oxidize and form a high impedance ground path. Poor grounds caused by oxidation can in themselves create and radiate RF fields by rectifying current.

 Any corroded joint in which ground currents are flowing can rectify current and transmit RF radiation. A rectifier passes current in one direction and opposes the flow of current in the opposite direction. A common manmade rectifier is a diode. In nature, rectifiers are common in the presence of high intensity RF fields.

 Corroded magneto distributor cap contact springs (the ones in the towers where the harness fits into) can radiate large amounts of RF into avionics. Cleaning the contact springs with contact cleaner usually helps.

 A good ground for RF frequencies is much harder to achieve than a good DC ground. As current frequency increases from DC to AC, the opposition to current flow becomes less resistive and more dependent upon the capacitive and inductive characteristics of the ground connection. Thus, a good RF ground has low DC resistance and reactance. This is generally accomplished by having:

Low resistance. Ignition harness shielding to magneto cap should be less than 3 milli-ohms. On Slick harness make sure that that the silicone covering is cleaned off the wire braid at the spark plug end so that the spark plug attachment hardware makes good electrical contact with the wire braid on the harness lead.

Clean, paint free surfaces. For example, new Bendix D-2000/D-3000 ignition harnesses are supplied with a cover that has paint where a portion of the capacitor trap attaches. This attachment is part of the RF ground for the capacitor and should not be painted.

If using a bonding strap, for example between the engine and mount, the strap should be as short and as fat as possible. A short, fat strap increases the width to length ratio and lowers high frequency impedance. Large surface area means low inductance.

All ground points should be at the same potential (voltage). This is achieved by connecting all grounds at a single point or by grounding at multiple points on an equipotential ground plane.

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