Ham Radio General Class Practice Test 2025 - Free Ham Radio Practice Questions and Study Guide

An NVIS (Near Vertical Incidence Skywave) antenna is typically installed at a height between 1/10 and 1/4 wavelength above ground. This specific height range is effective for achieving nearly vertical radiation patterns, which are well-suited for short-range communication, often within a few hundred miles. When the antenna is set up at these low heights, it allows the radio waves to reflect off the ionosphere at steep angles, enabling effective communication over shorter distances, particularly important in emergency situations or local nets.

Heights below 1/10 wavelength can result in poor radiation patterns and reduced effectiveness of the antenna for the intended NVIS application. Conversely, installing the antenna significantly higher, such as near a half wavelength or full wavelength, would decrease the vertical incidence of the radiation, making it less effective for the short-range applications that NVIS antennas are designed for. Thus, the range of 1/10 to 1/4 wavelength strikes the right balance for NVIS operation, facilitating optimal communication performance.