ARRL Technician Practice Exam

What could cause your FM signal to interfere with stations on nearby frequencies?

1. Using a directional antenna

2. Microphone gain too high, causing over-deviation

3. Low transmitter power setting

4. Correct spacing between frequencies

The correct answer is: Microphone gain too high, causing over-deviation

The correct answer highlights that if the microphone gain is set too high, it can cause over-deviation of the FM signal. In frequency modulation (FM), over-deviation occurs when the modulation of the carrier frequency exceeds the allowed limits, resulting in excessive frequency swing. This can cause the signal to occupy more bandwidth than intended, leading to interference with adjacent channels or stations on nearby frequencies. In FM transmissions, maintaining proper deviation limits is crucial to ensure that the transmitted signal does not spill over into adjacent frequency channels, thereby causing interference for stations that are operating close by on the spectrum. The other scenarios—using a directional antenna, having a low transmitter power setting, and ensuring correct spacing between frequencies—do not inherently cause interference but can play a role in the effectiveness and reach of a signal. A directional antenna may actually limit interference due to its focused signal pattern, while a low power setting is less likely to create interference because it reduces the signal's reach. Proper frequency spacing is also designed to minimize the risk of interference, so these factors do not contribute to the problem in the context of FM signal modulation.