[TowerTalk] NVIS (not exactly towers, but HF)

[jimlux]

I guess if you have a tower, you're not so interested in NVIS <grin>
Interesting paper (behind IEEE paywall unfortunately) in this month's 
Antennas and Propagation Magazine.  The authors have a series of papers 
over the past few years of interest, looking at various performance factors.


P. J. Coetzee and W. P. du Plessis, "Performance Limiters of 
Near-Vertical-Incidence Skywave Propagation: A Scientific Approach," in 
IEEE Antennas and Propagation Magazine, vol. 62, no. 3, pp. 39-44, June 
2020, doi: 10.1109/MAP.2019.2943313.


Abstract:
Near-vertical-incidence skywave (NVIS) propagation is defined as 
providing continuous coverage from nearly 0 km (just beyond the line of 
sight) to a couple hundred kilometers from the transmitter with no skip 
or dead zones. NVIS communications are especially effective during 
disaster-relief operations when infrastructure is severely damaged. The 
ability to accurately determine the performance limiters of NVIS 
propagation can help in the planning of high-frequency (HF) (3-30 MHz) 
emergency communication links. In the literature, widely varying radial 
distances (from as few as 50 to up to 160 or even 320 km) for the 
coverage attainable by NVIS propagation have been reported. It is very 
difficult to plan an NVIS link for homeland security or disaster relief 
when the published guidelines vary to such a degree. In this study, a 
scientific approach was utilized to determine the NVIS performance 
limiters for varying solar conditions, times of day, and geophysical 
locations.