What is the approximate length of the wire for a horizontal loop tuned at 7.15 MHz?

A horizontal wire loop is a full-wave antenna. To calculate the physical length of the wire in meters, amateur radio operators use the practical formula 306.3 divided by the frequency in MHz. This accounts for the velocity factor and edge effects of wire loops. By calculating 306.3 / 7.15 MHz, we get approximately 42.84 metres, making 42.80 metres the closest and correct answer. Other options act as distractors for different calculations. For example, 300 / 7.15 gives the free-space wavelength of about 41.96 metres, and 143 / 7.15 gives approximately 20 metres, which is the length of a half-wave dipole.