Home Brew – NVIS Antenna

This is a down and dirty, under 1,500-word DIY article on how to build a NVIS (Near Vertical Incident Skywave) Antenna. There are several dozen articles on doing this available via the ineterwiz however hopefully this write-up simplifies the build for you. Might as well learn from my mistakes.

If you do not know what a NVIS antenna is and why it is a great addition to your antenna farm, go and read these four articles. The first being from NC Scout titled, Near Vertical Incidence Skywave – Simplified, then NVIS I, NVIS II, and NVIS III authored by Key Pounder and published on NC Scout’s site, Brushbeater.

At a 100,000-foot level though, a NVIS antenna is a dipole antenna that has a steeper transmit angle than a traditional horizontal flat-top dipole antenna and is located closer to the ground at between 8 to 15-feet Vs. a traditional 1/4λ height; let’s say 30 to 60-feet over tera firma. This allows you to transmit to other stations closer to your AO that you may skip over using a flat-top horizontal dipole antenna. Think of the skip bounced off the ‘F’ layer of the ionosphere being 25 to 50-miles Vs. 200 to 300-miles. The German Army developed this procedure during WW II to communicate with troops via the airwaves closer to the transmitting station.

Traditional dipole antenna radiation Vs. NVIS radiation

I started out building my NVIS antenna using the directions posted on the DX Engineering site as my blue-prints for the project. Although you can buy a kit from DX Engineering, I had plenty of hardware around the redoubt so I decided to save a few bucks. Below is my Mise en place for this build. Hams are the true scroungers of this earth.

PVC Schedule 40 pipe. Three sizes 3″, 2 1/2″, & 1 1/2″ On hand
Green 14-gauge, stranded, insulated wire From Home Depot
100-feet of Green Para cord From Tractor Supply
4-dog bones (Insulators) Ham Radio Outlet
Can of Camo Green Paint Local Hardware store
Misc. nuts, bolts, self-taping screws, PL-259 connectors, wire ring connectors, Self-amalgamating tape, etc. Local Hardware store
PVC Schedule 40 reducing couplers, 3″ to 2 1/2″ and 2 1/2″ to 1 1 1/2″ Local Hardware store

Here are the steps of my build:

1) Cut the three pieces of Schedule 40 pipe to 5-feet and joined them together using PVC reducing couplers. In the end the pole was just over 16-feet long.

2) Once this was accomplished, I pre-drilled the upper end (smaller neck) on the two reducing couplers then inserted three, #8 x 1” self-tapping stainless steel screws into each collar to secure the section of pipe into the reducer.

3) Once assembled and fastened I stood the 16-foot pole up. The rigidity of the pole was less than satisfactory so I took it down to stiffen. To stiffen up the poll I inserted 1” x 3-foot section of PVC Pipe into the 1 1/2—2” section/joint and secured the stiffening pipe with one 3” x 5/16 stainless steel bolt. Then took a 1 1/2” x 3’ section of the pipe and inserted it into the 2” – 1 1/2” joint. Secured with one 4” x 5/16 stainless steel bolt.

4) Happy with the stiffness of the pole now I wiped down the pole with isopropyl alcohol. Once that was accomplished, I took some 150-grit sandpaper and ruffed up the pole. After another wipe down with isopropyl alcohol I hit the pole with camo spray paint. Let it dry for two hours then hit it again with another coat of the paint.

5) With this all accomplished I cut 8-inches off the top of the antenna. At the 15-foot mark I drilled a 5/16” hole through the top of the mast for the bolts that will be used for the antenna wire connections.

6) I measured out two lengths of insulated stranded 14—gauge wire in 65-foot lengths (63-feet plus 2-feet). Once laid out I then measure 26-feet from one end and marked with tape. Then from the other end I measured out 39-feet. In theory you should end up close (within an inch) of where you marked the wire earlier. At that point take off 3-inches of the insulated cover. Once done duplicate another length of wire for the other side of the dipole antenna.

7) Inserted a 1 1/4” x 5/16” stainless steel machine screws from the inside out of the holes you drilled at the 15-foot mark. Then wrap the bare part of the aforementioned wire around one of the bolts once, soldered the wrapped wire around the bolt for security. Once soldered I secured the wire between two washers and a wing nut.

8) By now you should have one wire attached to one bolt with one end 26-feet long and the other end 39-feet long.
Similarly I attached to the other bolt the other length of wire. Now I had the 40-meter and 80-meter wire attached to
each bolt.

9) With that done, I measured from the bitter ends of the wires 1-foot and attached the dog bones by wrapping on its self (Not soldered, for future length adjustment if needed) to all four bitter ends. Then attached 25-feet of para cord to each 40-meter wire (25-foot section of wire) dog-bone and 9-feet of para cord to the 80-meter (38-foot sections of wire) dog-bones. After the para cord was attached to the dog-bones on the 40-meter lengths I measured back from the dog-bone 20-feet and marked the length. Similarly, on the 80-meter lengths I measured seven feet back on the para cord and made a mark. The reason for this is you want the marks on the para cord to be at the stakes you insert into the ground, so the wires are at the proper angle which in part makes it a NVIS antenna. These angles will give the antenna the optimal angle for transmitting.

10) To attach the coax to the antenna I made a ‘Y’ pigtail with a 12-inch piece of coax. One end of the coax I separated the inner core from the outer woven shield about 3-inches long. Tinned the core and then the shield. Then affixed one, 10/12-gauge 5/16th-inch ring wire connectors to the tinned core and the other ring wire connector to the woven shield. Often, I see folks just clamp down on a ring wire connector with pliers however I used solder for double security as this is a weak point of the antenna. The other end of the coax ‘Y’ I fastened a PL-259 connector. Once the pigtail was done, I fastened one of the ring wire connectors to one of the bolts that supported one side of the antenna wire and then the other one to the other bolt. You can see this in the next picture at the top of the frame.

11) To the PL-259 side of the pigtail I screwed in a SO-239 female to female barrel connector for a PL-259 male plug. Then attached 75-feet of coax cable to the pigtail. Last, I wrapped this three-joint connection with self-adhering amalgamated tape to try and keep moisture out.

With the help of my neighbor (A 14-year old General licensed ham operator) we Iwo Jima’d the antenna up, set the para cord guide lines with tent stakes. Once the antenna shaft was supported, we pulled out the antenna wires and set the stakes using the previously marked para cord. Fed the coax into my shack and then to my Kenwood, TS-590S transceiver. Fired her up, tuned up the antenna using the Kenwood’s internal auto-tuner and…Well… It would not tune. DAMN!

At this point the sun was setting so I called it a night. Headed to my computer and started searching for an answer.

After several days of scratching my dome, I ran across an article on the ineterwiz from Shawn T. Donley N3AE and Steven O. Urquiza N3IDX, who had similar poor results when they built their NVIS antenna. It came down to the fact, that they, as I, were using a longer coax cable than what the military typically uses by 50’ or so. The article went on to state that if you installed coils about 7-inches along each wire from the top of the pole it would tune up. In the article there were formulas for wrapping the wire around specific sized PVC pipe which is located on page 3 of the article.

I followed the instructions and wrapped my coils. Added an additional three or so feet to each length as the wound coils shortened each leg-wire of the antenna (with coil in place 40-meter length still needs to be 25-feet and 80-meter with coil in place still needs to be 38-feet in length). Put the antenna back together, hooked up the coax, and my neighbor and I raised the antenna once again. Re-staked out the guide lines and antenna wires. Ran inside to the shack, fired up the power supply, then the radio. Hit the auto-tune button on the TS-590S… VIOLA, the antenna tuned up on 40 & 75/80-meters. Literally, several minutes later I made my first QSO with a gentleman in Cuba. An unusual long distance for a NVIS antenna but I will take it.

Since that antenna build, I have used the antenna at this past year’s (2018) June Field Day weekend and countless other events. I really experienced the NVIS antenna’s value in this past Octobers (2018) Pennsylvania QSO contest. While it was easy to hit the far-flung counties of the state, with a traditional dipole antenna and its height, I couldn’t hit the more local counties without the NVIS antenna. When I switched to the NVIS antenna and called CQ, I was inundated by QSO requests. HAVE FUN!

Freedom Through Self–Reliance©

References:

https://brushbeater.wordpress.com/2015/10/19/near-vertical-incidence-skywave-simplified/

https://brushbeater.wordpress.com/2016/08/15/nvis-explained-i/

https://brushbeater.wordpress.com/2016/08/15/nvis-explained-ii/

https://brushbeater.wordpress.com/2016/08/15/nvis-explained-iii/

DX Engineering

Shawn T. Donley N3AE and Steven O. Urquiza N3IDX

 

 

By Published On: May 18, 2019Categories: Comms25 Comments on Home Brew – NVIS Antenna

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25 Comments

  1. Wynn May 18, 2019 at 08:44

    I have been using a NVIS antenna as my primary for a little over 3 years. I hsed the kit and plans from DX Engineering and for the pole I used a 3 section painters pole from Lowe’s. It has been through multiplehurricanes and wind storms with no issues. I have had excellent performance on digital modes with this antenna. I haven’t really tried Voice much due to the band contitions as of late and running barefoot makes voice tough. Great write up JMac!

    • johnyMac May 18, 2019 at 09:07

      Thank you Wynn! The kit is a really good one and probably would make the build I described a bit less involved. \”/ With that written, my heritage is Scottish, so I tend to be frugal. MrsMac claims I am cheap.

      I know you are probably in the midst “planting season” however, don’t be a stranger Brother. Doing a net this coming Sunday night if any like minded subscriber to AP would like to join in.

      73 & God Bless

      • Homer May 18, 2019 at 09:54

        What time and freq is the net?

        • johnyMac May 18, 2019 at 10:59

          Homer,
          Go to my site, Unchainedpreppers.com (You can view as a guest) scroll down the home page list of Boards till you come to RADIO. Click on that Board and look for Sunday May 19, 2019 PACE (Primary, Alternate, Contingency, Emergency) subject. I invite folks to join in or just listen on a Short Wave Radio as long as that radio has a SSB (Single Side band) feature. If you do not have a SSB feature, you will most likely only hear one side of the conversation.

          Thanks for asking Brother.

      • Wynn May 18, 2019 at 10:45

        JMac I must say the DX Engineering kit is well worth the money! It’s been out in the weather since March of 2017 and still going strong. Feel free to email me with your bet schedule and I will see if I can make contact! Thaks JMac!

  2. Anonymous May 18, 2019 at 08:53

    5

  3. Homer May 18, 2019 at 09:49

    When u made the close in nvis contacts during the Pa qso party was you on 40m or 80m? In my experience 40m goes way to long to be useful for nvis due to the current solar cycle. 80m in the day works awesome for CLOSE nvis. I recently made two contacts about 35-40 miles away using 80m and a low antenna. Great article as usual.

    • johnyMac May 18, 2019 at 10:52

      Homer, I do not remember whether it was 40 or 80-meters. LOL. I forget what I had for dinner last night. Oh wait it was steak.

      This antenna is a great addition to anyone’s antenna farm. Again, I routinely take it down and travel with it to use in the field. I really like Wynn’s suggestion to use an extendable painters stick.

      Thanks for sharing your experience Homer.

      73 Brother!

  4. Bryce Sharper May 18, 2019 at 14:02

    Johnny Mac,

    Great article. I clicked through the link on the NVIS matching network then read about a similar antenna system on Harris’ website. The Harris NVIS system uses a tuner to transform from the coaxial feed to the mast/dipole system with a matching impedence. The tuner was designed for ALE and can match to the next frequency in the sequence in 200 ms. I’m not sure if the length of the coax had too much to do with the inability to match other than the 2-way path loss of the wave reflected off the antenna feed would be 4 dB. The spec for RG-8X is 2 dB/100 feet at 30 MHz. I think you’ve designed a good transformer (balun) and matching network with these series inductors allowing you to transform and match the single-ended input from your pigtail to the dipoles.

    I need to get my general and try some NVIS. Great article.

    • johnyMac May 18, 2019 at 16:01

      Thanks Bryce for the additional link. I will definitely check it out.

      Now you getting your General Ticket…I know, I know it does take time however my now 15-year old neighbor got his General when he was 13. Just poken the bear. \”/

      This is what I tell everyone who asks, “How do I get my Ticket?”
      1) Get the ARRL study book for Technical level,
      2) Set up a ARRL account (Free by the way) and as you progress through the book take the practice exams, and
      3) Go to your ‘type of phone’ app store and download the Technical exam questions.

      Okay, read one chapter a week and take the exam questions in back of the book as you do the chapter. When waiting in line at the DMV, sitting in a Doctors waiting room, sitting at a red light; pull your phone out and answer the questions for the chapters you have completed. Last, starting about half way through the text book, sign on to the ARRL site and take a practice exam. When you consistently get a 80% or better on the practice exams it is time to take the exam.

      73 Brother

      • Bryce Sharper May 19, 2019 at 22:51

        Thanks Johnny. This article prompted me to re-read some of NC Scout’s articles on NVIS. This reminded me I have HF privileges using CW and I can buy an HF transceiver for $40 while I save for a fancy CommRadio CTX-10. I have no excuses!

        I also re-read parts of Peter Parker’s Hand Carried QRP Antennas which contained a lot of suggestions for squid-pole HF rigs with end-fed antennas diagrams of cheap DIY antenna couplers. I have a lot to try.

        ’73
        Bryce

        • johnyMac May 20, 2019 at 11:48

          LOL Bryce, every time I start learning code I get distracted – Bummer.

          Although the CTX-10 is a great QRP radio, do not hesitate picking up a standard 10-160-meter transceiver rig that has power up to 100-watts. Quality second hand units like the Icom 735 can be purchases for under $300-. A good indication if a used IC-735 is in good condition is if it still has the front plastic plate intact. I found a IC-735 for Patriotman that was in very good condition and the cost was around $250-.

          All good stuff! 73

          • Bryce Sharper May 21, 2019 at 00:43

            Thanks. Do you think learning Morse code is worth it? I think I found a good learning resource but I don’t want to waste the time and effort on a single-band, CW-only rig if there’s no one on the other end within NVIS range. It seems like guys are doing Morse to make round-the-world contacts. Do I have this wrong?

          • johnyMac May 21, 2019 at 12:28

            Mmmmm, learning CW, is it worth it? My first inclination is yes. My second thought is there are other things needed to be accomplished before CW. They are:

            > Although it is ‘nice to have’ the Extra ticket the General will suffice. I have learned so much with my General it isn’t even funny.
            > With that written; learn phone first, then digital, and then last CW. It is one of my goals to get above 15-words a minute on CW so if you know a good
            program please share it with the group.
            > The great thing with CW is, it is a code within itself. The pun is intended. ;-) I know hundreds of hams between the ages on 15 & 93 years old and
            nobody less than 50 years-old is proficient in CW. It would be a great skill to have in a grid down situation. Add to this statement, many hams who
            use CW have their own code/abbreviations that they only use among themselves. Think Brevity Matrix.

            The best part of CW is that it is easier to make contacts, especially in the current poor propagation situation we are currently in, on the other side of the globe. The second best part of CW is you can throw a QRP antenna in a tree, hook up to a QRP radio and with CW make contacts around the globe under 10 watts. QRP radios tend to be light and small as you know.

            When MrsMac and I moved off our boat to dry land. I needed some additional land based tools. I went to my big box hardware store and was amazed by the selection of hammers. Hammers that have a specific purpose for the job at hand. In my opinion, communication is similar.

            Sorry for the long response. I am procrastinating from going out and tilling the garden. \”/

          • Bryce Sharper May 23, 2019 at 21:49

            I ordered this program. It was kind of a bait-and-switch. It turns out to be 12 hours of practice to 5 WPM and 30 hours to 20 WPM. While it would be cool to “Work the world” on a 9 v battery, I want reliable regional comms. I can’t verify that anyone in the EMS monitors HF ham bands for emergency CW transmissions either to bail me out hiking or hunting, so I can’t see how it would be a better investment of my time than studying for my General and buying an HF radio.

            I’m coveting the Comm Radio CTX-10 if for no other reason than it has the most readable data sheet I’ve seen.

          • johnyMac May 23, 2019 at 22:14

            The CTX-10 is a great radio. Size, weight, internal tuner, battery life, it goes on and on. And yes a EMS monitor will not know code. LOL.

            Because we are hams it is in our blood to want to help when needed. With that written if while using phone you can only hit Bill not the 911/EOC center, Bill will be glad to help out.

            All good stuff Brother!

  5. mikrat May 18, 2019 at 15:03

    I too have used NVIS many times and great results.

    What I’m not understanding on the DX Engineering site as well as the http://arrl-ohio.org/SEC/nvis/Modified%20AS-2259%20NVIS%20Antenna.pdf – is why try to use the Military wire lengths for the Ham 40 & 75/80 meter bands?

    They both use:
    25 feet each leg (50′ Total) is good around 4.5 mHz +/- , and 38 feet each leg (76′ total) is good around 2.92 Mhz (buy using 234 / Mhz = 1/4 wave Length} – Both of these put you outside the ham band from the start.

    Why not use the correct wire length for the bands:
    For the 75/80 and 40 meter bands – When 234 / 7.2 Mhz = 15.44′ per side for 40m, and 234 / 3.82 Mhz = 29.1′ per side for the 75m band.

    This should negate the need for added coils.

    And for a short mast – this is a compact option that can even be back-packed:
    https://mgs4u.com/product/mk-2-series-14-ft-2-in-masts/

    • johnyMac May 18, 2019 at 16:19

      milkrat interesting question. I am sure there are dozens of ways to make the same antenna not unlike there are dozens of ways to make an apple pie. Staying with the apple pie analogy; the first time I made an apple pie I stayed with the recipe. When I make another NVIS antenna, I am sure things will change on that build too. After-all, you can never have too many antennas at your disposal…Right?

      Thanks for the link to the fiberglass mast. I am just too Scottish to pay out $129.95 for a mast though. LOL!

      73 Brother!

    • Bryce Sharper May 21, 2019 at 00:45

      How much power were you using?

      Even if you use the correct length for the coils, you still need to transform from 50 ohm single-ended coax to differential 377 ohms for the dipole. A matching network (antenna coupler) is still needed.

      • Bryce Sharper May 21, 2019 at 10:07

        Typos: I meant to say, “Even if you use the correct length for the dipoles, you still need to transform from 50 ohm single-ended coax to differential input impedance of the antenna terminals. The input resistance of a resonant half-wave dipole is about 70 ohms[1]

        [1]Stutzman and Thiele, “Antenna Theory and Design (2nd)”, pg 171 and 179

  6. Lima Sierra 08 May 19, 2019 at 08:52

    I’ve made a couple of dipoles that worked very well on NVIS that are very portable.
    https://wirenutcomms.wordpress.com/2017/09/17/new-dipole/

    • johnyMac May 20, 2019 at 11:50

      Thanks for sharing LS08.

      I love the extension cord wraps for the antenna wire. All good stuff.

      73 Brother

  7. MW PREPPER May 19, 2019 at 16:35

    Thanks for the info on the NVIS antenna. A great weekend project, no doubt. Just got back from the Dayton Hamvention. Checked out all the antenna manufacturers & most were offering some good deals on their products. Now going through all that literature I picked up! Checked out your web site & info about the net. Just keep hammering out more good stuff is all I can say.
    73

    • johnyMac May 20, 2019 at 12:02

      Thank you MW Prepper for your positive comments.

      MrsMac and I went to the Dayton/Xenia Ham Fest in 2017. Picked up a few great deals at the flea market and got a smoken deal from HRO on a new Yaesu 817. MrsMac loved watching the people and food. We shared a picnic table with an Amish ham operator and his family for lunch one day. That man sure knew his radio equipment. LOL. I forgot what rig he had but he ran it off of several 12-volt batteries in parallel. He charged the batteries while running a small steam engine that he used to make home made ice cream.

      This ham convention should be on everyone’s bucket-list to visit at least once in their lives.

      73 Brother…

  8. Patriotman May 21, 2019 at 22:30

    Sounds like we have yet another project to complete on my next trip to the Redoubt, brother! Hope the Mrs is doing well! God bless.

    For all others reading, we tested his setup on my used Icom-735 and got contacts from Texas to Slovakia. So, can confirm it worked beautifully.

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