The field meaning: A skip zone is the region between the outer limit of reliable ground-wave coverage and the first returning skywave for a given frequency, time, antenna, and ionosphere.
What is really happening
As frequency, takeoff angle, and ionospheric height change, the first-hop return point moves. NVIS can fill regional coverage that a low-angle antenna skips over.
Do not confuse it with this
A skip zone is not a permanent circular dead area; irregular ionization, scatter, terrain, and different antenna angles can produce signals inside it.
Use it deliberately
For regional work, choose a band below the critical path limit and an antenna with useful high-angle radiation; test alternate bands and document the actual coverage at that hour.
Decision boundary
Operating shorthand and propagation models are tools for making a better decision, not proof of a path, contact, or safety condition. Confirm with current rules, measured signals, weather, and the complete station.
