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Near vertical incidence skywave (NVIS) propagation refers to a specific method of radio wave transmission that is particularly effective for short-distance communications, typically within a range of about 300 miles (or 500 kilometers). This technique involves transmitting radio signals at high elevation angles, usually between 60 to 90 degrees.

When these high-angle signals are transmitted, they are directed toward the ionosphere, which reflects the signals back down to the earth, allowing for effective communication over relatively short distances. This characteristic makes NVIS ideal for local communications, such as emergency services or during situations where other forms of communication might be compromised.

Using NVIS is particularly beneficial in covering areas that may not be reachable by other propagation methods due to terrain or man-made obstacles. Therefore, the key element of NVIS is its reliance on high elevation angles for effective communication at shorter distances, effectively making it a favored choice in specific operational scenarios such as portable operations or during a natural disaster.

In contrast, the other choices do not accurately describe NVIS propagation. It is not limited to low-frequency waves or restricted to night time, nor does it represent a form of ground wave propagation, which operates differently by following the curvature of the Earth and typically covers much shorter distances than sky