ARRL Technician Practice Exam

What could be happening if another operator reports a variable high-pitched whine on the audio from your mobile transmitter?

1. Noise on the vehicle's electrical system is being transmitted along with your speech audio

2. Interference from local radio stations is affecting the audio

3. Your transmitter is malfunctioning due to overheating

4. The antenna is improperly tuned

The correct answer is: Noise on the vehicle's electrical system is being transmitted along with your speech audio

When another operator hears a variable high-pitched whine from your mobile transmitter, it often indicates that electrical noise from the vehicle is leaking into the transmitted audio signal. This phenomenon can occur when the vehicle's electrical system generates noise, which can be picked up by the microphone or audio processing circuits of the transmitter. High-pitched whines are commonly associated with alternators, ignition systems, or other electrical components in a vehicle. They are particularly noticeable when the engine is running, as the operation of the engine and its associated electrical systems can introduce interference into the signal being transmitted. This scenario highlights the importance of maintaining a clean electrical environment for communication equipment. Proper grounding, the use of ferrite beads, and quality power connections can help mitigate the effects of electrical noise produced by the vehicle. While other issues, such as antenna tuning or transmitter malfunction, could potentially affect signal quality, the specific nature of a high-pitched whine usually points directly to interference from the vehicle's electrical system.