ARRL Technician Practice Exam

What is meant by the term radio horizon?

1. The distance over which two stations can communicate by direct path

2. The frequency at which signals are absorbed

3. The area covered by a single repeater

4. The line of sight distance between two stations

The correct answer is: The distance over which two stations can communicate by direct path

Radio horizon refers to the distance over which two stations can communicate by a direct path, primarily limited by the curvature of the Earth and any intervening obstacles. When two radio stations attempt to communicate, they rely on their signals propagating in a line of sight manner. This means that if there are no obstructions like hills or buildings in the way and if the antennas are high enough, the stations can effectively communicate. This communication distance is not solely dependent on geographic features, but also factors like the height of the transmitting and receiving antennas play a critical role in determining the effective radio horizon. Frequencies used for communication can also impact the radio horizon due to differences in how different wavelengths propagate in the atmosphere. The other choices introduce concepts that are relevant but don't accurately capture the essence of what is meant by radio horizon. The frequency at which signals are absorbed does not define the distance over which communication occurs. Similarly, the area covered by a single repeater pertains more to the repeater's technical specifications than direct communication between stations. Lastly, while line of sight distance is a contributing factor to the radio horizon, it is not the full definition, which emphasizes the communication capability specifically.