Flagpole Antenna – My Version

Those of us who live on small, urban lots, or live under the auspices of HOAs or CCRs, routinely lament the frustrations of a limited ability to get on HF with a good antenna system. In recent decades an entire subculture of ham radio has sprung up in the area of stealth/invisible antennas that can be put up either hiding in plain site, camouflaged to blend in, or both. One of the most unique, to me, is the “Flagpole” antenna. This article describes my experience designing and building my version. Obviously this isn’t the only way to build one, and it certainly has shortcomings. However, it works surprisingly well.

Let me pause a moment up front to say that I didn’t get pictures of all parts of this build. Where necessary I’ve tried to provide more detail or create drawings to aide in understanding my logic and methods. Comments and questions are certainly welcome, as long as they are constructive and genuine. Finally, this post was created for information and entertainment purposes only. I make no claim that this project will meet your needs or work in your situation. You are also solely responsible for any attempt to recreate this project and I’m in no way liable for injury (from your own actions or those of your spouse against you) should it happen. So with all that out of the way, let’s begin!

Why a Flagpole?

“I pledge allegiance to the flag, of the United States of America, and to the republic for which it stands, one nation, under God, indivisible, with liberty and justice for all.”

United States Pledge of Allegiance

First off, I’ve always wanted a flagpole in my yard that will let me fly the American flag 24/7 (lighted of course) and show my love of this country. I happen to be proud of what it represents, and even though we have our issues as a nation, we are still the greatest country on earth, in my opinion. I personally think every home should display the flag, but that’s me. And, don’t get me started on those with no respect for it. That would be 3 or 4 posts at least and would likely result in my being booted from every social media platform in existence so we will leave that one alone.

Second, although I’m not subject to the issues associated with HOAs or CCRs, I do live in a 100+ year old historic home, in a historic district, on a very small, corner, urban lot. In fact, my back yard is literally a 5′ wide strip that runs between my house and the neighbor’s driveway. That’s not a lot of room for an antenna of any sort, so that leaves two “side” yards and the front. The side away from the corner, where my patio is, has the added issue of being surrounded by power and service lines so that a permanent antenna of any height is also a no-go. What remains is the front and corner side of the lot. Since I also need the cooperation and approval of my wife (and the included WAF – Wife Acceptance Factor) whatever I put up would need to look good and not be an eyesore to her or the neighbors. That being said, I do have an understanding wife who also happens to be licensed as a ham (technician) so that does help.

Third, I didn’t want to go to the effort of installing a bunch of radials in the grass that would inevitably find their way to the shaft of my lawnmower blade. I know the grass is supposed to grow up and pull them down (so they say) but I also know my yard and my lawnmower. Since it’s mostly weeds, that perspective is likely suspect. Enough said.

So being retired Navy, and of a patriotic nature, I began looking for a flagpole antenna design and that’s when I experienced the sticker shock of ready made commercial offerings. Now don’t get me wrong, the products I looked at appear to be well made antennas and I think they are worth the price being asked. The testimonials look genuine and likely based on sound engineering, practical designs, and experience. However, being limited in funds (remember that 100+ year old houses also require periodic work) I needed a different solution. I also like to build things (this is of course the DIY Ham) so this looked like an interesting challenge and an opportunity to solve two issues in one build. After a good deal of searching, I ran across this YouTube video by John Portune, W6NBC, describing his experience with DIY flagpole antennas. Based on the information presented in John’s video, and the realization that I already had some of the materials he had used on hand, I began doing targeted research and came up with a design that would fit my needs, and pass the all important WAF.

The Design & Odd Parts

If you take the time to watch John’s video, you will probably note that one of his first versions was built from the aluminum poles used by the military to hold up camouflage netting. These have been a staple offering at hamfests for years, and are relatively cheap to obtain. It also happened that I had 11 of these that were given to me by my neighbor (the one with the driveway 5′ from the back of my house) when her husband passed away a few years ago. Having used these to put up a 40′ dipole support mast at our last field day in 2019, I knew they were pretty strong, but could be wobbly due to the flexibility of the slip joints between the poles. I also found that they would just barely slide into 2″ schedule 40 PVC plumbing pipe. Looking further in my material pile, I found a 5′ length of 2″ aluminum tubing, also schedule 40, and a plan started to come together. Figure 1 shows the basic sketch of the antenna I came up with. For the most part it was followed, with a few minor tweaks along the way.

Basically, it’s an Off-Center Fed Vertical Dipole antenna. Based on John’s information and my own research, I knew that putting the feed point off-center would yield an impedance of around 50 ohms and feeding the coax up the center of the lower, aluminum tubing section, would keep it from looking odd and be more like a flagpole. Also, since the camo poles (the green section in Figure 1) fit inside of 2″ pvc pipe, the pipe could act as a radome of sorts for the upper portion, and create a consistent 2″ pole from bottom to top.

Parts List

Here are the basic parts/materials needed to build a 20′ flagpole/antenna:

• 1 – 5′ section of 2″ schedule 40 aluminum tubing/conduit
• 2 – 10′ sections of 2″ schedule 40 pvc pipe
• 1 – 2″ pvc coupler
• 1 – 2″ pvc cap
• 1 – 5′ section of 1 1/2″ pvc pipe
• 1 – 48″ section of 1 1/2″ hardwood dowel
• 5 – aluminum camo net poles (approx 46″ in length)
• 30+ – 10-24 x 3/4″ stainless steel machine screws
• 8-10′ – RG8/LMR400 coax
• 1 – remote tuner
• 1 – 1:1 choke
• 1 – can of spray paint (in whatever color you desire, I used white)
• 1 – flagpole truck/pulley
• 1 – rope cleat
• 50′ – poly rope for use as the halyard
• 10″ – 3″ diameter heat shrink tubing

Figure 2 shows one of the camo net poles used to build my antenna. As you can see there is a joint collar at the bottom that is welded to the main tube and a tapered nipple at the top that fits neatly into the lower end of the next pole. They are also a butt ugly green, so hiding them inside the 2″ pvc will help the aesthetics as well. Those are the basics for the flagpole/antenna itself. Of course you will need some way to mount it and also a way to get the transmitter feed out to it. You will also need a selection of tools such as:

• Drill (cordless or wired)
• Drill bits (various sizes
• Tap for stainless steel screws
• Countersink bit for stainless steel screws
• Hacksaw
• Handsaw or miter saw
• Various other hand tools

Upper Section Build

The top section consists of the aluminum camo poles sleeved inside the 2″ pvc pipe. This is then capped by the 2″ cap after attaching the truck/pulley just below the line where the cap will seat itself. Start by assembling the camo poles as shown below:

Two sections should be held tightly together (and aligned straight) while drilling and tapping for the stainless steel screws (Figure 3). This will lock the two together and provide significant strength to the overall pole. Each screw must be countersunk below the level of the joint collar in order to clear the 2″ pvc later. Place two screws at each joint, 180 degrees apart. Also, the line of screws on each side of the assembly should form a straight line up opposite sides of the assembly. Although I didn’t do it in my assembly, you may want to add a product, such as Jet-Lube, to the joint to minimize corrosion and promote good electrical conductivity. Now would also be a good time to lightly sand the aluminum weld joints level with the joint collar. Continue this process with the remaining 4 poles and you will end up with a length of about 19′. Measure from the bottom (widest point of poles) up 16′, mark and trim using a hacksaw. This will give you the proper length for the upper section. Next you will need to sleeve the pole assembly with the 10′ sections of pvc pipe, starting at the bottom.

Begin with the first 10′ pvc pipe and before sliding it over the camo pole assembly, place it alongside with the bottom ends flush. Mark the pvc with either a sharpee or tape at each of the joint collars to allow additional fasteners to be used to connect the pvc to the assembly. Once the marks have been made, slide the pvc pipe over the camo pole assembly taking note of where the joint screws are in relation to the circumference of the collar and pipe. The bottom of the camo pole assembly and the bottom pvc pipe should be flush as shown in Figure 4. At each of the collar marks on the pvc, and at 90 degrees from the camo pole assembly screws, mark for another set of screws, 180 degrees apart, to lock the pvc to the internal poles. This will add more strength to the overall assembly and still remain flexible to sway gently with the breeze.

As discussed earlier, the joint collars are a tight fit, but as can be seen in Figure 5, there is a gap between the body of the poles and the pvc pipe. This is not an issue except at the point where the two pvc pipes come together and at the top of the last camo pole where you had to trim the length. You will need a spacer insert for these two places. Since the gap is approximately 1/8″, I was able to use the inner plastic ring I had saved from a kapton tape roll that was trimmed to fit. This makes up the gap and allows the two pvc pipes to be anchored at the transition point. A short section of pvc pipe with a section removed could also be used as long as the thickness is about 1/8″.

At the locations where you marked for the additional screws, drill, tap, countersink and install them. The depth of the countersink is not as critical for these screws, but should be somewhat even with the pvc pipe. Be sure to drill, tap, and countersink for screws at the transition ring as well leaving enough to engage the upper pvc pipe that is added next.

Once you complete the first 10′ section, measure from the top end of the pvc pipe to the top end of the inner camo pole assembly. This should be approximately 6′. To this measurement add an additional 6″. Use this total to mark and cut the upper pvc pipe before sliding it over the remaining camo pole assembly. The additional length is to allow for the installation of the truck/pulley assembly later on without making contact with the camo pole assembly. Once you have it cut, repeat the marking of the joint collars done for the lower section and then slide it into position. As you slide the two pvc pipe sections together, consider applying a small amount of sealant to the joint to keep water out of the interior of the antenna. Drill, tap, countersink, and install the holding screws, including through the lower transition ring and the upper shim ring between the top of the camo pole and the pvc pipe. Set the top section of the flagpole antenna aside for now.

Lower Section Build

The lower section of my antenna consists of a 4′ section of aluminum 2″ tubing cut from the 5′ piece listed in the materials list. The remaining 12″ will become the portion that mounts the overall assembly to the base. Since the antenna design is that of a vertical dipole, the upper and lower sections must remain electrically isolated from each other and the mount. To accomplish this the 4′ x 1 1/2″ hardwood dowel is cut into two equal pieces. One is used to connect the upper and lower antenna sections and the other to connect the lower section to the 12″ mounting tube. It turns out that the internal diameter of the camo poles is just over 1 1/2″ and with a couple of pieces of heat shrink tubing as shims, the dowel is a snug fit. For the 2″ aluminum tubing, a section of 1 1/2″ pvc pipe, with similar heat shrink shims makes up the difference for the dowel in that part (and the mount). The 5′ section of 1 1/2″ pvc should be cut into a 12″ section for the mounting tube, and the remaining 4′ for the lower antenna section.

Prior to installation, both dowel sections must be prepared by boring a hole through the center of the dowel between 13 and 14″ deep. This is then followed by a cross hole that intersects the end of the center hole to allow the coax to pass, up to the union between upper and lower sections and from the bottom of the lower assembly through to the upper dowel as shown in the details of Figure 6.

Once the interior holes have been drilled, feed the coax through both ends and slide into the 1 1/2″ pvc pipe and then into the aluminum tube. You should end up with 10-12″ of hardwood dowel protruding from both ends of the tube with coax extending out both as well. The lower end should be of sufficient length to reach the remote tuner output (12-24″) and the upper end should be trimmed and separated into the braid and center conductor. The braid will need to be connected to the lower tubing and the center conductor prepared to eventually connect to the upper section when the two are joined. The lower end will slide into the mounting tube with the 2″ pvc coupler used as an isolator between the two aluminum tubes. You will need to cut a slot in the upper part of the coupler to allow the coax to pass out. The hardwood dowels and pvc pipe will all need to be anchored in place using suitable screws. Take care, however, that you do not penetrate the drilled passages in the dowels that contain the coax to prevent damage. In my case I used screws commonly used to hang cement board (because that’s what I had on hand) and predrilled the aluminum tubing. The completed lower assembly should look something like Figure 7. Note the coax extending off to the right. (Incidentally, the other pvc item in the picture is the base of an experimental 6m center feed vertical dipole that happens to work very well and will likely be the subject of a future post.) At this point, all that remains is to assemble the upper and lower sections of the antenna, add the flagpole hardware, install it, connect it, and test it on the air.

Final Assembly

Assembling the final flagpole/antenna begins with joining the upper and lower sections together. In my case, I left the center conductor bare and sticking up along side the hardwood dowel that would slide into the upper section to make contact with the inner portion of the lowest camo pole. This friction fit appears to be working well. I also ended up with a gap (on purpose) between the upper and lower sections to prevent electrical contact between the two. This was covered with a 10″ section of 3″ diameter heat shrink tubing and is the small skinny section a little less than 1/4 the way up the finished pole in the opening picture.

As you can see it’s barely noticeable at a distance, and once painted, barely visible. Figure 8 provides a close up view of the heat shrink after it has been painted white. A word of advice, to minimize frustration slide the 3″ heat shrink on to one of the sections prior to joining them. This will make it easier to simply slide it into place and shrink it with a heat gun. You may also want to fill the space with dielectric grease to ward off water intrusion.

Once the two sections have been put together, take the time to paint the entire assembly. Once dry, the truck/pulley must be attached at the top as shown in Figure 9 (leave room for the cap), and the halyard cleat, shown in Figure 10, added at a convenient height (about 3-4′ above ground). I also fitted the top of my flagpole with a 2″ ball (also shown in Figure 9) . I scavenged this from a Harbor Freight telescoping flagpole I use as a temporary mast for portable work. I simply through bolted it to the 2″ pvc cap and friction fit the cap to the top. This will allow me to change out or service the truck/pulley, should I ever need to do so.

The last step to putting the flagpole/antenna in the air is installing a suitable base mount, preferably one that will allow the pole to be lowered to the ground for servicing and to prevent damage in severe weather. I built my mount from salvaged aluminum channel and thick walled square tubing and is shown in Figure 11. I’m hesitant, due to the stresses involved at the ground for a 22′, 2″ mast, and the potential liabilities associated with it, to share details of my own solution. Although mine is robust (in my opinion) I do not want to potentially lead someone astray in this particular area. DX Engineering is one source for ground antenna mounts that will work well with this build at reasonable prices. I’m not saying you can’t build your own mount. I actually encourage you to do so, if you have the knowledge or know someone who does and can help you. That is what this site is all about, doing it ourselves. However, you need to do your homework and fully understand the physics and forces involved before attempting a DIY mount. You also need to understand the liabilities you assume when you undertake such a project. Okay, off my soap box. On with the show.

Hooking it Up & Getting on the Air

Obviously, the main purpose for this exercise is to end up with a usable antenna. In order to do that it needs to be connected to your transceiver or transmitter/receiver. For this type of antenna that will require the use of a remote tuner, and I also highly recommend using a 1:1 choke (not a balun as it is routinely and mistakenly called) between the tuner and the coax feeding the shack to keep common mode currents out of the shack.

The tuner I’m using is the LDG RT-100 with the RC-100 Controller as shown in Figure 12. The RT-100 is mounted at the base of the antenna (in my case inside a plastic container) and the RC-100 sits in the shack next to the radio providing power to the tuner over the coax. As recommended, I also have a DIY choke that is wound on a FT-240-31 toroid to cover 80-6m (9 turns of RG-8X) and placed in a project box with SO-239 connectors on either end as shown in Figure 13. Both the tuner and the choke are in the plastic container with the coax coming up through the base via buried conduit. The signal then exits via a bulkhead SO-239 on the side facing the flagpole. Attached to the outside end of the bulkhead connector is a lightening arrestor followed by the antenna coax. The arrestor, the tuner, and the flagpole base are all connected to an 8′ copper ground rod driven in next to the base. All of this is shown in Figure 14, and before I get the comments about no wrap on the exposed connectors let me say that I’ve held off on that until my initial testing is complete. I will get to that soon, I promise.

The tuner is in the bottom of the box, held down with double sided tape, with the choke sitting on top. Also shown in the box, are a 14 gauge electrical wire and a cat6 cable, both running with the coax through the conduit back to the shack. The wire is an extension of the shack and station grounds to the antenna grounding system and the cat6 is for future expansion/projects.

Once everything is set up and verified working, it helps to add a little bit of landscaping to make the project look good and more like a flagpole. Obviously, that part is my wife’s area of expertise (although I did have to haul the pine bark, and dirt, the landscape stones…) and I’m happy to let her handle that part since she enjoys it so much and it shows in Figure 15.

Results

So, does it work? In a word, yes. Is it perfect? No, but I’ve made some decent contacts locally on 10m ssb and along the eastern seaboard (US) on 40m using FT8 and JS8Call. I’ll continue testing to see what the limits are, but it appears that it will work from 40m to 6m with about 1.6 tuned swr and 80m between 2 and 3 swr. I’ll update this post as I work more with it. Thank you for reading this far and please provide comments and feedback. We are always learning in this hobby, and we learn best when we share information and experience. God Bless.

WA4OPE – Dave Hewlett

Updates – Performance

Since I published this article I’ve been doing some testing and have also finally plotted the antenna in EZNEC (yes I know I probably should have done that first but, you know…).

Performance wise, the antenna tunes up on all bands from 80m up through 6m with no problem. I am considering adding the 4:1 balun back in to make it a little easier on the tuner. I’ve been able to make FT8 contacts through out a good portion of the US and the Caribbean on 80m, 40m, and 20m, and I’ve finally been able to check-in to Winlink Wednesday on HF for the first time. Overall, I’m pleased with the antenna and the flagpole as well.

Plots

Below are plots from EZNEC Demo v.6.0. The main reason I never plotted the antenna in the first place was the fact that I got a missing file error every time I tried to run, reload, etc. the program. After a little research, I determined that it was issues with the VB runtime module that had been installed last summer. After removing both and reinstalling the software, it finally works. So without further ado, here are the plots:

If you have any questions please let me know. Enjoy.