"Editor's Note: Due to the popularity of some of eHam's older articles, many of which you may not have read, the eHam.net team has decided to rerun some of the best articles that we have received since eHam's inception. These articles will be reprinted to add to the quality of eHam's content and in a show of appreciation to the authors of these articles." This article was originally published on: 11/18/2002
N.V.I.S. Portable Antenna
By Stephen T. Reynolds W4CNG
A.R.E.S. DEC Metro-Atlanta
There are several articles describing the N.V.I.S. antenna theory and a few ways to build them. Portable and Mobile operation using this style of antenna produces a good path of communications in the 100-250 mile range. Adapting a mobile station quickly and easily is the main feature of this article, plus low cost and ease of construction. Here is how to do two bands really easy for about $20. First is the hardware list.
Home Depot 100ft 12Ga Stranded RED wire. ($11.00)
2 #12 Wire Ring-Lugs with 3/8 inch holes. (.30)
2 3/8x24
4 3/8 inch flat washers (.20)
2 Quick Disconnect antenna bases ($6.00) HRO/other Mail order house.
2 Dog bone end insulators and 40 ft nylon rope. Junk box
Take the wire and cut at 33ft. This gives you 33ft for 40 meters, and 67 feet for 75 meters, the two most popular N.V.I.S. bands for A.R.E.S. use. Crimp and solder one of the ring-lugs to one end of each piece of wire. Using the 3/8x24 fine thread bolt and two flat washers, bolt the ring lug to the quick disconnect base (one flat on top and one on bottom of lug). You can have an option here. Use one quick disconnect for both sets of wire lugs (dual band antenna) or build 2 separate antennas and deploy the one you will be using. I built two separate antennas. The quick disconnect was chosen as lot's of us use singleband mobile HF antennas with quick disconnects. For portable operation, remove the mobile vertical antenna, connect the N.V.I.S. antenna and quick disconnect to your antenna base on your vehicle.
The picture below shows how the finished product looks connected ready to test. This is one of the one piece 3/8x24 single hole to SO-239 mounts (solid brass center pin, no pressed fitting).

Here is the testing of the antenna. The ground side of the antenna is your mobile. String out the antenna away from your mobile to a fixed structure further than the 33/66 ft of antenna you have. Red wire was chosen, as it is easy to see when strung at 3-5 ft above the ground. You do not want the antenna higher than 5 ft. The testing and tuning here is in the authors' deed restricted neighborhood front yard. The antenna wire is strung across the front lawn at about 3 ft above the ground and tied to the tree in the far left of the picture.

Tuning/trimming of the antenna is then done for resonance in the part of the band you will be operating. I allow an extra 12 inches of wire folded over at the end of the wire for future adjustments. There is no substitute for a good antenna bridge to get an antenna resonant. The antenna shows a near perfect match at 47ohms. No tuner will be needed here.

The #12 stranded wire gives +/- 80Khz on 40 meters and +/- 60Khz on 75 meters for less than 1.7:1 VSWR. Not bad for a simple wire antenna that took 30 minutes to build and 15 minutes to tune.

Both antennas coiled up and ready to put into the ready bag for deployment.
Good Luck
| W6JAK | 2022-10-27 | |
|---|---|---|
| Re: N.V.I.S. Portable Antenna | ||
| HA7WX, I agree with everything you say. The point of my brief post is that readers should know this antenna will work but it is not optimal. To your point, many hams throughout the years have used sub-optimal antennas with great enjoyment and no one should be discouraged from doing so. 73 Jack Reply to a comment by : HA7WX on 2022-10-07 While you are right about the height, it's not always convenient to reach, the military isn't either using such a height, yet it's still possible to make contacts and I would not discourage folks to experiment, which is the true essence of HAM radio, answering that question: what sort of contacts can I get with a particular setup? My last experiments on 80m NVIS were with a dipole with its max height at 20 feet, ends at sg like 6 feet. I had signals of s9 to s9+10 @ 10W LSB and I did steady contacts on a 0-150 mi radius. Now my craziest setup has been a non tuned 'dipole' with the feed-point at ground level, one half on the ground and the other half at a maximum of 12 feet, did regular AM contacts on 80m with a station 75 mi away. Having fun with antenna experiments is what is left to the most of us as I'd have no time nor the necessary tech background to build my own TRX. Reply to a comment by : W6JAK on 2022-09-21 Will this work? Yes. Well? No. Most of the RF energy will be absorbed by the ground. NVIS antennas work most efficiently between 30 and 40 feet depending on frequency. | ||
| HA7WX | 2022-10-07 | |
|---|---|---|
| Re: N.V.I.S. Portable Antenna | ||
| While you are right about the height, it's not always convenient to reach, the military isn't either using such a height, yet it's still possible to make contacts and I would not discourage folks to experiment, which is the true essence of HAM radio, answering that question: what sort of contacts can I get with a particular setup? My last experiments on 80m NVIS were with a dipole with its max height at 20 feet, ends at sg like 6 feet. I had signals of s9 to s9+10 @ 10W LSB and I did steady contacts on a 0-150 mi radius. Now my craziest setup has been a non tuned 'dipole' with the feed-point at ground level, one half on the ground and the other half at a maximum of 12 feet, did regular AM contacts on 80m with a station 75 mi away. Having fun with antenna experiments is what is left to the most of us as I'd have no time nor the necessary tech background to build my own TRX. Reply to a comment by : W6JAK on 2022-09-21 Will this work? Yes. Well? No. Most of the RF energy will be absorbed by the ground. NVIS antennas work most efficiently between 30 and 40 feet depending on frequency. | ||
| W6JAK | 2022-09-21 | |
|---|---|---|
| N.V.I.S. Portable Antenna | ||
| Will this work? Yes. Well? No. Most of the RF energy will be absorbed by the ground. NVIS antennas work most efficiently between 30 and 40 feet depending on frequency. | ||