ARRL Technician Practice Exam

What can cause a broadcast AM or FM radio to unintentionally receive an amateur radio transmission?

1. The receiver is unable to reject strong signals outside the band

2. The frequency is not properly tuned

3. The radio's antenna is damaged

4. The amateur transmission is too weak

The correct answer is: The receiver is unable to reject strong signals outside the band

A broadcast AM or FM radio can unintentionally receive an amateur radio transmission primarily due to the receiver's inability to reject strong signals outside the intended frequency band. Broadcast receivers are designed to accept a range of frequencies, and if a strong signal from an amateur radio transmitter falls within or close to that range, especially if it is operating nearby on a similar frequency, the receiver may inadvertently pick it up. This situation can occur due to the lack of selectivity in the radio’s design. Most consumer radios are built with broader bandwidths and may not have the sophisticated filtering that separates amateur radio frequencies from broadcast frequencies effectively. Thus, when an amateur radio station transmits at a high power, the signal can easily bleed into the adjacent bands of the broadcast radio, leading to unintended reception. The other options describe scenarios that either would not result in the unintentional reception of an amateur signal or are less likely to be the cause. For instance, if the frequency is not properly tuned, it could lead to static or poor reception rather than receiving an amateur signal. A damaged antenna might reduce reception capabilities overall, but it would not necessarily lead to picking up amateur signals specifically. Lastly, if the amateur transmission were too weak, it wouldn't cause interference at all.