I've made dozens and dozens and maybe more NVIS antennas with a couple of designs published out there. I also spend quite a bit of time in the field testing and playing with them, usually fed from a military HF manpack rig or an Elecraft KX3. Since I'm at or near QRP levels my antennas have to work well to make up for the flea power and they usually do that very well.
The basic criteria for an NVIS antenna is something that gives an upward lobe within the frequency range that NVIS propagates, which can be from a very low frequency to about 10MHz depending on propagation. Most hams with a horizontal wire antenna already have an NVIS antenna and don't realize it.
The most gain for a horizontal dipole or similar antenna is about a 1/4 wavelength above ground and for most people the 40m band is about the highest band you use, so about 33ft would be the highest height above ground for a 40m NVIS antenna or a multi-band NVIS antenna. Go lower and you start to reject distant signals arriving at a lower angle, but your upward gain starts to fall off rapidly.
Here is a mock up brochure for a multi-band NVIS HF antenna I designed with a separate mount and ground radials for an NMO VHF/UHF mobile antenna on top. Look at post #3 in this thread which has the description and brochure:
http://forums.radioreference.com/am...able-antenna-recommendations.html#post2339024
This is similar to what you guys probably used in the military but much more lightweight and versatile. With all that said, what design has the OP decided on?
prcguy
We used these in the military and got pretty good results for the medium range transmit region. I have been looking around and have found a design I am planning on building and just wanted to know if anyone has built their own NVIS antenna and how they liked the performance, any issues that were unexpected as the build went along..