NVIS

NVIS wave propagation
While the ground wave (blue) cannot propagate, HF coverage is ensured via the reflected skywaves (red) in the first hop (~ 500 km).

With NVIS ( N ear V ertical I ncidence S kywave ) refers to a special transmission mode on the medium and short wave . The electromagnetic wave is radiated very steeply (at an angle of 80–90 °) into the sky in order to reduce near fading effects and to suppress the dead zone . The frequency used is below the MUF (Maximum Usable Frequency) and above the LUF (Lowest Usable Frequency). The range around 5 MHz can be used for this purpose. This is why more and more telecommunications administrations are also assigning frequencies or frequency ranges in this band to radio amateurs . In contrast to the shrinkage-reducing antenna , which only sends flat radiation, NVIS only works with steep radiation.

This method is used by broadcasters, radio amateurs, the military and aid organizations.

literature

• Roger L. Freeman: Radio System Design for Telecommunications. Wiley, 2006.

Web links

Commons : NVIS  - album with pictures, videos and audio files

• Building instructions for the construction of an NVIS antenna for amateur radio bands