FCC Technician Exam Question Of The Day (T7B09)

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

NJ2X Notes:
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.