Q) What could be happening if another operator reports a variable high-pitched whine on the audio from your mobile transmitter?
A) Noise on the vehicle's electrical system is being transmitted along with your speech audio
The ignition system on any vehicle is often the source of RFI. Ignition and injection systems both include an inductor which produces a high-voltage pulse for firing the spark plug. The spark plug creates a considerable amount of RFI which is radiated throughout the car's wiring system. This can cause a great deal of noise on a mobile ham radio. Fortunately, there are several effective techniques which can be used to reduce or eliminate RFI generated by a vehicle including: filtering the power and replacing worn ignition wires and plugs.