80 Meter NVIS Antenna

80 Meter NVIS Antenna – Don’t Get Hung Up on Theory

Watch the following video to see how to build and erect a basic 80-meter NVIS antenna. After watching the video, please read the field test stories below the video as this design flies in the face of theoretical 80-meter NVIS antenna design.

I’m the Chief of Communications for the New England Forest Rally and we need to rely on NVIS to solve a tough comms problem. CLICK or TAP HERE to read about it.

CLICK or TAP HERE to download a simple plan and material list of this antenna.

Field Testing Tales

I was first introduced to this simplistic antenna five years ago when I first started to learn CW. My mentor Jim Cluett, W1PID told me about his discovery of this low-to-the-ground antenna because he used it to get onto the NH-VT traffic net each night from his home in Sanbornton, NH.

I’m the Chief of Communications for the New England Forest Rally and we have a very difficult communications issue on one of our stages in South Arm, Maine. CLICK or TAP HERE to read about this tough comms problem. This year, 2019, was my second year in the job and I decided to do an experiment with 80 NVIS with two other operators.

I set up this same antenna as you see in the video above, but it was even more wretched. It averaged just 18 inches above the ground. I was transmitting at 13 watts on my Elecraft KX3 and two other operators heard me crystal clear ten miles away. It’s very likely the success was due to ground wave.

However, during the same test, my mentor 100 miles away was monitoring the test out of general interest and he heard me just fine. I had a conversation with him while I was waiting for my fellow operators in Maine to set up their 80-meter NVIS antennas just 10 miles away.

We were operating phone (SSB) because that’s how the comms would happen during the race. I’m doubtful my meager 13-watt signal would travel 100+ miles via ground wave over some semi-mountainous terrain, but I could be wrong. It absolutely might be why the other two operators were able to hear me and I hear them just ten miles away.

A week prior to the test at South Arm during July of 2019, I did a similar test with this antenna design in my backyard. That antenna was probably only 30 inches above the ground. I had successful SSB communications with my mentor who was 8 miles away and another old friend, Dave Benson, K1SWL, who was about 40 miles away. Once again, I was fairly low power, 10 watts, and I don’t believe that ground wave would make it 40 miles.

If you’re an antenna expert and can point me to a document that really shows how far an 80-meter ground wave can travel at different power levels, I’d be forever grateful. Please add those links in the comments below. 73 Tim Carter – W3ATB

9 thoughts on “80 Meter NVIS Antenna

  1. Your height above ground for a NVIS antenna flies in the face of engineering theory for an NVIS antenna. In short, an NVIS needs to be .15 to .25 wavelengths above ground for good performance. Yes, one will work just a few feet above ground and will be quieter than one higher up, but at what cost? Quieter simply because of ground losses.
    About the time I built my inverted V modeled on the Mil AS-2259 I studied (including consultation with RF engineers) the why’s and wherefore’s of NVIS height above ground. ALL verified the optimal height at .15-.25 lambda above ground

    There are numerous references re NVIS engineering including this one as a starter:
    Military HF Radio Communications and Near Vertical Incidence Skywave Propagation
    https://www.youtube.com/watch?v=4EadY6eDKhs&t=2s

    Jus’ sayin’

    • Jim,

      You’re absolutely correct about the theory. I decided to add much more content above AFTER you posted your comment. The content helps explain the context of the antenna and how well it actually performs.

      One of my projects with HF comms, as crazy as this sounds, is to put up the most wretched antenna configurations possible to see what works. Who knows, I may write a short book about it.

      Wretched Antennas You’d Never Think Would Work
      by: Tim Carter W3ATB

  2. Some folks in Silicon Valley who like to play with Mil equipment set up and NVIS similar to what you have and got excited because they proved it would work when they were able to contact colleagues 10 miles away.

    I worked with an engineer “back in the day” who was a also a ham. He told me a tale of soaking his Mom’s cotton clothes line in salt water, then loading ’em up and made HF contacts until the “element” resistance dried up the moisture. I saw a YouTube video once upon a time where a couple of guys loaded two 50’s vintage Buicks parked nose to nose, making contacts afterwards. Radio is PFM (pure frickin’ magic) where wierd stuff can sometimes work.

    I noted the distance of the folks you contacted with your NVIS, all approx 100 miles away and less. You probably know that max theoretical reach for NVIS to be 400-500 miles. I’ve gotten good reception and S9 reports from stations at 400 miles (Sacramento area and Truckee, CA area to Tehachapi, CA. While camping a few miles north of Truckee with another ham, we experimented with the performance difference between my inverted V AS-2259 (elements cut for 40M) and a 40M horizontal dipole almost colocated. Feed point for my NVIS was 15′ (very close to the .15 lamda for 7MHz) and elements sloping at 45 deg. Feedpoint to my friends dipole was similarly at 15′. Expectation was the horizontal dipole would outperform my inverted V connecting to the Tehachipi station. Nope. My antenna had a report of S9, my friends antenna S7.

    Another occasion I set up for 40M connections to Winlink HF (40M) gateways while in the Sierra for an equestrian event. Had a perfect, <1.5:1 VSWR with the NVIS over grass in a local park. In the Sierra, over dry, rocky ground, the VSWR was crap.

    Just goes to show that under varying conditions up to and beyond standing on your left foot and putting your right pinky into your left ear can get good results. However, for reliable results, one goes with what the engineers say, else the AS-2259 (admittedly, a compromise antenna for use in a combat theatre) would be strung out a few feet off the ground to trip sappers as they tried to sneak into an HQ camp 😉

    • Well, I have to respectfully disagree with your last sentence. The antenna you see in this video is reliable. Perhaps you overlooked the part of the story where my mentor used the antenna to check in repeatedly with the NH-VT traffic net.

      No worries, you do what’s best for you and for our NEFR rally where we need an antenna we can deploy in minutes, we’ll use this antenna. Believe me, I’ll report back next year after the 2020 NEFR where eight HF operators will be on that South Arm stage using NVIS, ground wave, or pure magic.

  3. Great article and simple set up. I live in a place where I have lots of space but I have few optimal places to string antennas. My 40/75m trapped dipole is strung from about 25 feet up at one end with the other end trap being at 10 or so feet with the 75m stub down to about 3 feet. I call it the “dog leg dipole” and I’ve worked all over the world with the configuration on 40m and a significant number of countries on 75.

    All of my antennas would be considered compromised designs due to simple things like not having a tower, large trees or natural structures in convenient places. But I’ve strung verticals, dipoles, deltas and quads in strange configurations and gotten very good results. So although the “rules say”, at the end of the day if it works, don’t knock it.

    • John,

      Exactly. There are the purists like Jim above, and then there are the rapscallion antenna stringers like us. INSERT Happy face emoticon here.

  4. I worked on a deep ground penetrating radar project at the Air Force Research Lab in Rome, NY for a number of years. A lot of fiddling went into making MW to UHF antennas that effectively radiated into the ground. And wideband, portable, and a few other things. The important thing to understand about antennas over a dielectric half-space is that the dielectric constant of rock might be 4-8, and that of water is 80. So, your tuning changes drastically as you change the height, and above different soils or rock. Sitting on top of the surface, you can use the equations for stripline, but above that, there’s too many terms to figure on the back of an envelope. If you point a VHF yagi into the ground, the directors “lengthen” into directors somewhere less than a wavelength away.
    It looks like you didn’t use a balun anywhere, so it would be interesting to see what happens when you run the coax through some ferrites. Also, how about the polarization between xmit & rcv?
    You probably have a lot of ground wave propagation, because your antenna looks a lot like the Navy’s VLF setup in Cutler, Maine. Except you don’t have a megawatt transmitter and aren’t at 24 KHz.

    • I run that antenna into my Elecraft KX3 that has an internal tuner. Since it’s a balanced dipole, the small tuner has no issues giving me a 1:1 or 1:1.5 SWR. Great story you shared! TNX for doing that!

  5. Loved all the ham talk here although I come here most for building. I do have a warm place in my heart for ham radio and the people who practice it. It reminds me of a Dave Barry quote: “Guys like to do stuff! That explains everything from mailbox vandalism to the space shuttle.” Ham has a much deeper purpose in mind but I thing the analogy still works. Keep on sharing!

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