NVIS, or Near Vertical Incident Skywave, is a method of radio communication that uses shortwave frequencies to achieve effective local and regional communication. This is particularly useful in areas where line-of-sight communication is hindered by obstacles like mountains or buildings.

1. High Angle Radiation: NVIS antennas emit radio waves at high angles, typically between 75 to 90 degrees. This allows the signals to reach the ionosphere quickly and reflect back to the Earth's surface.

2. Short to Medium Range Communication: By reflecting off the ionosphere, NVIS covers a range typically from 30 to 400 miles, bridging the gap between line-of-sight VHF/UHF communication and longer-range HF skywave communication.

3. Antenna Types: Common NVIS antennas include simple dipoles, inverted V antennas, or loop antennas, often positioned only a few feet above the ground or on rooftops.

4. Ionospheric Dependence: The effectiveness of NVIS depends on the current state of the ionosphere, which is influenced by solar radiation and time of day. It's most effective at frequencies between 1.8 MHz and 10 MHz.

5. Applications: NVIS is widely used in military, emergency services, and amateur radio operations, especially in rugged terrain or during natural disasters when traditional communication methods are disrupted.

This method offers reliable, consistent coverage over a specified area, making it a vital tool in various communication scenarios.