Set up is simple. A 3’ piece of pipe is driven half way into the ground. The PVC Tee with the dipole is slipped on top of two sections of mast, and the mast is slipped over the pipe. The dipole is unreeled and stretched out. Two more pipes are driven a couple of feet past the ends of the dipole and two sections of mast are put over each one. The dipole ends are tied to the ends of the mast with string. The weight of the dipole will tend to pull the end poles inwards, so the end poles are guyed to keep them straight up and the dipole horizontal.
Most of the literature shows the NVIS using 3 reflector wires. When I set it up in my yard for initial testing the ground was extremely dry and I had trouble getting a good match with just three wires. It got a better match with 5 and very good with 7, so that is what I settled on for mine.
The wires are about 4’ longer than the dipole. For quick set up they have loops tied in the ends and a black tape marker in the center. The wires are unreeled and the center placed next to the center pole. The ends are stretched out past the end poles. Small cut dowels pushed through the loops at the ends into the ground hold them in place. The other wires are set out at about 2’ increments. Note that no effort is made to “ground” the wires. They are simply laid on the ground. I can set the NVIS antenna up in about 15 minutes by myself. Having a couple of helpers makes the job go even faster.
Skywave propagation requires a minimum level of ionization in order for the ionosphere to direct the signals back to earth. With a given level of ionization the maximum frequency will decrease as the incidence angle is increased. The “critical frequency” will be quite low, much below the Maximum Useable Frequency (MUF) that is more commonly reported for radio communications. The critical frequency may not reach 7 MHz at the low part of the sunspot cycle, even during the day. For emergency communications one for the 75 meter band might be more reliable than one for 40 meters. Mine was made for 40 meters since that is the band I typically operate for Field Day.
I found the NVIS antenna to be a useful addition for FD. My normal FD antenna farm consists of a dipole at about 30’ (still consider fairly low with a high take off angle) and a vertical with raised radials. In one case I made signal strength comparisons with a known station about 90 miles away. I could not copy him on the vertical. He was about S6 on the regular dipole and a good S7 on the NVIS antenna. I also found that the NVIS antenna is very quiet and often helped produce solid copy when the other antennas had difficult copy. It would definitely not be the only antenna I bring to Field Day, but is a valuable addition, especially considering how easy it is to put up and take down.