NVIS (Near Vertical Incidence Skywave)

NVIS, or Near Vertical Incidence Skywave, is a radio communication technique where signals are sent nearly straight up into the atmosphere. These signals bounce off the ionosphere and come back down to the Earth's surface nearby, allowing reliable communication over medium distances (approximately 50 to 300 miles) without requiring ground-based repeaters. It's often used in military and emergency communications, especially in rugged terrains or situations where maintaining direct line-of-sight is difficult. NVIS provides a way to cover areas close to the transmitter quickly and efficiently, using specific frequencies and antenna setups optimized for near-vertical signals.