Plain-language answer: NVIS uses strong high-angle HF radiation that returns over nearby and regional distances when the operating frequency is below the usable ionospheric limit.
Why it matters in the antenna
It is a path strategy, not a product label or coverage promise. Frequency, absorption, noise, antenna height, geometry, and pattern all matter.
What to verify
Compare 80 and 40 meters with a low horizontal or inverted-V wire while recording time, distance, noise, and reports.
The common mistake
Calling every low wire NVIS without checking frequency and pattern.
Operating boundary
Use the exact documented component, geometry, frequency, power, duty cycle, clearances, and feed/return system. Begin tests at low power and stop for heating, arcing, damaged insulation, or unstable supports.
