Radio frequency interference (RFI)

Electromagnetic interference (EMI) or radio frequency interference (RFI) is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source (non-resistor type spark plug). RFI is any unwanted radio frequency signal, which interferes with another, desired radio frequency signal. Ignition system for RC gas engine in most cases causes RFI.

Receiver should be placed min. 30 cm (12 in) away from the ignition system. In general, as far away is possible from the ignition system. Avoid metal lever for throttle.

3-5k ohm ceramic resistor in the spark plug suppresses ignition noise generated during sparking. It is strongly recommended to use resistor spark plugs in any RC model that uses on-board computer systems to monitor or control engine. This is because resistor spark plugs reduce electromagnetic interference with on-board electronics. If special care is taken, radio interference can usually be avoided. It is very important to know that RC gas engines can cause radio interference with 72 MHz radio systems.

You don't have to worry if you have a spread spectrum radio system (eg DSSS - direct-sequence spread spectrum, DSSS V2 - direct-sequence spread spectrum V2, FHSS, FHSS2, FHSS3, AFHHS - frequency-hopping spread spectrum, FASST - Futaba advanced spread spectrum technology).

Spread-spectrum telecommunications is a signal structuring technique that employs direct sequence, frequency hopping, or a hybrid of these, which can be used for multiple access and/or multiple functions. This technique decreases the potential interference. Spread spectrum generally makes use of a sequential noise-like signal structure to spread the normally narrowband information signal over a relatively wideband (radio) band of frequencies.