NVIS Propagation

Near-Vertical Incident Skywave (NVIS) is a unique propagation used with high-frequency (HF) modes to transmit to the distances that normal HF propagation won’t allow (too far for groundwave, but too short for skip).

NVIS propagation is accomplished by reducing the height of the antenna. As an antenna is lowered toward the earth, the angle that the antenna transmits upward increases. This means the transmission is going more “up” and not “out”. This upward angle makes the reflection back to earth much closer than it would be for an antenna at a normal height. The result is that HF communication becomes possible in the area that is normally “skipped”.

Generally speaking, you would reduce the height of an antenna by half to achieve NVIS transmission. However, realize that as an antenna is lowered, its inefficiency grows and must be considered.

Note: This can only be done with horizontal wire antennas (dipoles, end-fed half-wave, etc.), and cannot be done with vertical antennas due to the way they interact with the earth.