NVIS Antennas for 75/60/40 Meters By Stephen Reynolds W4CNG A.R.E.S. DEC Metro-Atlanta Ga. This article describes an antenna support mast, and a 3 band antenna system just right for A.R.E.S. or other In-Field Deployment. The existing 75 and 40 meter HF frequencies currently utilized for A.R.E.S. - N.V.I.S. dictated that a simple antenna design to support the new 60 meter band was necessary. There are lots of articles and designs on N.V.I.S. antennas that use a tuner and ground connection. This system is band resonant, does not need a tuner to work, and is much more efficient in use. This mount assembly breaks down into sections of 1.5 inch schedule 40 PVC that are all 34 inches long. The length was chosen so that it would fit into a commonly available 36 inch duffle bag, and 3 sections of pipe could be cut from one 10 ft section of pipe with a small amount of excess left over. The picture below shows the pipe sections and center mount assembly. 
The top section of the antenna is seen on the left with 4 additional 34 inch supports. The bottom frame assembly is to the right of the carry bag, with the 4 ground supports to the right. Simplicity in design was the first thing, with a cost of less than $20 for the PVC pipe, and $4 worth of #14 stranded wire. Add 6 white end insulators (dog-bones), a center insulator (Alpha Delta), 4 Double Coat Hangers and you are ready to go at under $40 for a three band Resonant N.V.I.S. antenna. Add a carry bag at $15 if you do not already have a suitable way to transport the antenna. Red wire was chosen so that it would be easy to see, plus you may want to add yellow flags in a couple of places depending on where the antenna is deployed and whether ground traffic will go by it. The next picture is of the center mast support assembly. I used 2 short 2.5 inch sections of excess pipe to join the T and 2 4-way joints. There are actually 6 different places the 4 ground supports can attach to. You chose the 4 you want to use. The two 4 way's need to be in line with each other and the T connection needs to be 90 degrees straight up. 
I used end caps on the 4 ground supports, and 4 in line splices for the mast supports. This mount may be assembled (friction fit) using up to 4 center supports. This would have the center of the dipole at 15 feet above ground. The 4/6 dipole elements deployed will provide guying of the center support. You can deploy any two of the three dipoles or all three. Two dipoles will run at 90 degree spacing to each other. With all 3 dipoles deployed, they are at 60 degree intervals. Yes you can leave one dipole coiled on the center support without affecting the tuning of the others deployed. Standard dipole lengths worked. An antenna bridge was used to check resonance. 75 meters came out to be 63 feet on each end, 60 meters came out to be 42 feet on each end, and 40 meters was 31 feet on each end. Your lengths may vary with local conditions. I left 18 inches of fold back on each end of the dipole at the end insulators so that on site tuning could be done if necessary. 
This is the completed mast assembly with one vertical support installed. If you are installing the system with 3-4 mast supports under it, you will want to unwind the dipoles you are deploying and have one person stand with the center mast while the ends are tied down. I use 3/16 inch black nylon rope for the end ties from the end insulators to whatever is being used to tie to. You can set it between trees, or in a small field and use tent stakes for tie down points. Remember to check tuning after installation. My antenna has +/- 75Khz on 75 meters, +/- 100Khz on 60 meters, and +/- 140Khz on 40 meters. Your mileage will vary. Using 100 watts on 75/40 and 50 watts on 60 meters, this antenna will work very well with very good efficiency because it is a tuned dipole. | 
