These are a few notes and links about NVIS propagation and antennas. This is in the context of setting up reliable-ish NVIS connections for regular morse QSOs for practice.
NVIS Propagation
Reflections at high angles (near 90 degrees) to the ionosphere only happen when below the critical frequency, known as f0F2.
For the UK, looks like f0F2 in daylight can be over 10MHz, but at night is likely to sit at 4MHz or possibly lower. So in terms of useful ham bands, 80m at night, 40m in the day are probably what will work best.
Maps of f0F2, both derived from
So, worth considering antennas for 80 and 40.
Antennas
Needs to cover 80m and 40m, with 60m as a bonus and possibly 160m if it can be done.
For me, I need an end fed wires for NVIS: https://practicalantennas.com/applications/nvis/end-fed/
One note from “The NVIS Illusion that is interesting:
Ground waves are transmitted by just about every antenna and extend to the local horizon. In the area close to the transmitting station it is likely that the ground wave will interfere with the received NVIS signal to produce fading (QSB) or other effects. It is a good idea to keep transmitted power low to mitigate this effect.
So low power might be sensible here, or experimenting with lowering power might be useful to stop ground wave propagation interfering with NVIS.