I’ve constructed a 144/440 Dual band Open Stub J-Pole Antenna.
I saw the plans for this on the internet (link to plans) by Allen Lowe (N0IMW). Since I had a Metal Fabrication background, I thought this would be an easy build.
I understand that everyone else in the world uses Metric, You can convert these numbers to MM and use 10mm aluminum rod and thread for the elements.
However I am not sure about the SO-239 adapter. I’ve read that it can be difficult to obtain the adapter in Europe. Any EU/Metric users, please help me out and give me details on what you did.
(Update 12/2018) Radio-Shack has since closed and the SO-239 adapter I listed on my blueprints are no longer in stock. You can find equivalents on ebay, amazon and other amateur radio or CB supply shops. It’s known as a “SO-239 to 3/8″-24 Adapter”. There are some variants so please make sure it appears the same as the one in my blueprint. You will need to check the diameter of shoulder on the insulation washer and adjust the size of the large to to make sure it fits.
Here is a Step-By-Step video with me stammering on. Getting a little bit better every time I make a video.
I did some minor changes from the above. Instead of using nuts I used pressed “PEM” nut on the underside and used thread protecting vinyl caps on the tips
It was a really fun and quick build. Plus it works okay. It’s no Diamond X510. What else do you expect for around $20 in parts? I love it.
If for whatever reason you can not build this. It is manufactured by the designer of this antenna and has them for sale on his website for a reasonable price. So check out ARROWANTENNAS.COM for the OSJ and other quality crafted antennas.
Due to many e-mails, I just want to state that I do not and will not manufacture these antennas for sale. I think those sold at Arrow Antennas are well worth price.
Antenna Gain, Pattern and NEC data
Some people were curious as to what the gain and pattern is of this antenna is. Arrow Antenna basically said they weren’t posting figures as competitors use gain as a marketing ploy and inflate numbers. However they did publish the patterns. I’ve tried to model the antenna in 4NEC2 without much luck. What I was inputting into NEC was nothing near comparable to what I and some others have measured. Thankfully I wasn’t the only one who was having issues modeling a J-Pole. C Bronson Crothers (AA1ZB) has talked about modeling the J-Pole and wrote quite a bit about it. Carol Milazzo (KP4MD) took it a step further and modeled the Open stub J-pole.
She modeled the antenna in various situations (mounted to mast, free space, free space with ground) and even published the NEC files for all to see. I’d strongly suggest to check out her website for the NEC files and other information that has helped me along in the hobby.
I took the files and messed around to see what happens.
Depending on the height about ground, your looking at anywhere between 3-7dBi (or .85dbd-4.85dBd) gain according to NEC Data. In the perfect world, if that antenna was fed with 50 watts, it would effectively radiate anywhere from 60 to 150watts. But that is in the perfect world which we are not in. Things like the type and length of coax used, connectors used, nearby structures, type of ground and a bunch of many other variables factor into how well an antenna performs.
In the antenna gain world you will see dBi and dBd depending on the manufacturer. You just don’t measure Decibels. In this case it’s used as a reference against either an isotropic antenna (dBi) or against a dipole (dBd). So if you see antenna readings in dBi, it’s in reference to a theoretical perfect antenna that radiates evenly in every direction. If you see dBd, the antenna is being compared against a half-wave dipole antenna. The difference between dBi and dBd is 2.15. dBd is comparison against an actual antenna. Some hams confuse dBi and dBd and some manufacturers confuse the buyer by not telling you the reference (It has 9dB of gain!!). Most manufacturers use dBi as it’s a bigger looking number. Just subtract 2.15 and you will know the gain compared to a half-wave dipole.
I bring up dBi vs. dBd gain for the reasons why Arrow Antenna doesn’t want to talk about it. An antenna shouldn’t be just about gain. It should factor in your shopping but you honestly won’t really know how an antenna will perform until you get it in the at. There are times I hear that the J-pole is no different than a dipole or even a ground plane which is not true. This particular antenna has some gain. It’s not as high when compared to the claims of large scale antenna manufacturers but considering the materials used, ease of assembly and use, I think this is a really good antenna. Okay, now that I am done ranting… let’s look at the pattern
This is a 3-d wireframe of the pattern (in gray) with an outline of the vertical polarization. The antenna is pretty much Omni-directional Horizontally. Vertically, the focus of energy is between 15 and 85 degrees. It would be ideal to mount the antenna above the roof line or at least 10ft off the ground as the signal radiates more from the side. This antenna wouldn’t really be ideal for Sat use as there is a huge null and less gain when looking towards the sky.
SWR and analyzer results
SWR plays an important role as well. If the antenna is not correct, some of the power sent to the antenna will come back to the radio. Modern rigs can see this and if too much power is coming back, the rig will step down in power to prevent damage to the finals. This usually happens if the SWR is above 2:1 or 3:1 depending on the rig. We need to get the SWR of this antenna down to 1:0 as possible. If this antenna is fabricated and assembled correctly, there should be little concern about SWR but it’s safe to make sure and check before using or even installing it
Here is what 4NEC2 Predicted On the VHF Side. By looking at the blue line towards the top of the image, you will see that it has excellent SWR throughout the 2M band. Looking at the green line, you will see that the impedance is also decent.
The UHF Side of the antenna doesn’t look so great when compared to the VHF side of the antenna. But it’s still useable. Once again these are predictions from the software. It’s doesn’t mean that’s how the antenna is going to exactly perform. But it will give you an idea of what’s going to happen. Let’s do some real measurements.
Someone let me borrow their Antenna Analyzer a few years back. You will see at 145.98Mhz I got a reading of 1.0SWR with a 51ohm impedance. The antenna was resting on a wooden chair so I am not sure what the value would be when fully installed but I don’t think it would change that much since it doesn’t need grounding. But coupling to nearby fixtures
After making various antennas, I felt I needed some kind of analyzer of my own. I purchased a mRS MiniVNA PRO. It covers HF/VHF only but it give me a better idea of how the antenna is performing throughout the band.
Here is a plot of the antenna installed. You will see that the antenna is usable from 135MHz to around 155MHz. It’s a nice wide band antenna and you will see how it differs from what 4NEC2 Predicted. But it’s not far off
Thanks to Jon (KI6RT), he provided some SWR plots from the VNA. What’s great is that he measured the UHF side of the antenna which I’m un-able to measure with the equipment I have. According to Jon, this was measure with the antenna installed at height
VHF Side
UHF Side.
Mounting:
Many people have asked “How do you mount this?” and “Could I mount this to a metal pole”.
I did not go into mounting because there are so many different ways you can mount this antenna that I couldn’t list it.
If you are mounting it to a metal pole, care must be taken that the pole does not extend past (above) the aluminum angle. If it does then it will become part of the antenna. I’m also not sure how the antenna would interact with other nearby metallic objects (fence, tower, other antennas).
Most people will mount this antenna to the top of a pole.
Known Issues:
Even though I did not design this antenna, I often get e-mails from people who had trouble with this particular antenna. I helped troubleshoot a lot of the issues and found out that the majority of problems were in result of the person not following the instructions as listed on either my or Mr. Lowe’s prints. Most common mistakes were people cutting the lengths short or people substituting the materials called with others. For those living in the rest of the world, I know you might have trouble trying to find SAE/Imperial material and will substitute 3/8″ with 10mm rod and hardware. I am not sure if they make a Metric SO-239 to 10MM adapter. But I’ve heard from multiple people that it work with 10mm.
Another common mistake is when it comes to testing. Testing should be done with the antenna installed or at least mounted to a pole to simulate an installation. Some people were laying the antenna on the ground, holding it with their hand or placing it against large metallic items (like a car) which will produce different readings. You won’t know how it performs SWR wise until you have it installed. Even though it’s rare, be prepared to install and remove the antenna multiple times while taking readings.
There is an issue which I haven’t touched on. Much care should be taken to prevent water from getting into the threads of the SO-239 adapter or in the adapter itself. Even more so if you live in colder climates where water can freeze and expand.
If you are unsure about cutting the elements to the proper length, it’s best to cut it a little longer and grind or re-cut the elements. It’s better to have elements that are too long instead of being too short. If you happened to cut it too short, it’s possible to use a coupler to adjust the length of the antenna but I would suggest re-making the element in question.
(Update: 3/29/2021) I’m now known as NT1K. I’ve made these prints when I was N1BMX. When I changed my callsign I kept the domain name (web address) for a few years and let it go. However, someone purchased it, tried getting money from me and decided to link it to an adult graphic website instead. I have nothing to do with the site and will be replacing any images/documents with the new domain. Thanks to K7NJO for the new images for this project.
Others who built the OSJ-Pole
I like when people send me their creations. Some follow instructions exactly while others are creative and use what they have to make a working antenna. Here are some links to those who also made the antenna. Maybe they can provide some insight into things I forgot.
F6FZU’s OSJ-Pole – French reader who managed to make the antenna using metric tubing as well as different materials while getting decent results on the analyzer. The one thing that stands out is that the angle he using to mount the elements is made from Galvanized dipped steal. I would avoid using steel at all costs. It appears he is taking steps to weather proof the steel.
Michigan Amateur Radio Alliance (MARA) – Couple of their club members (KD8PVS & KD8UCP) decided to build the OSJ-Pole using my prints. They did a very nice job and they also found another source for the vinyl caps and provided clamping and installation photos of their antenna. Nice job!
KI6RT’s QRZ.com Profile – In Jon’s profile, he built the OSJ-Pole. He manged to run the antenna through a high end analyzer showing SWR results of both the VHF and UHF portions of the antenna. It shows that at least the SWR is decent in both the bands.
Wonderful build was able to hit many repeaters with it attached to a pole stuck in a sleave in my front yard. Can’t wait until I get it up on the roof.
Thanks
thanks for the antenna plans and your contributions.
Wonderful work!
Thanks.
73 from Spain,Europe
Hello there….
Can I use a (10 millimeter) aluminum rod instead of [3/8″(9.5 millimeter)]….????
and if there is a very minimal variation in the length will that affect the efficiency of the antenna???
Thanks a lot.
I purchased one of these from my local LDS HAM guy, works wonders.
I was wondering if the antenna poles could be covered with electrical tape or any other kind of tape for camouflage?
I am currently looking to build this antenna but have run into a problem locating the aluminum rod in the length needed. I live in Toledo, Ohio if anyone has any idea where I can locate it please post in the comments. BTW. Home Depot does not sell it in 8 ft long pieces.
Amazon has many lengths to choose from. I ordered 2 rods, 72 inches in length, 0.375 diameter. Worked great for me and I had plenty left over for other projects.
McMaster-Carr is where I bought mine.
McMaster-Carr is where I bought mine.
Fastenal, Grainger, Metals Supermarket. The latter will cut to size at no additional cost.
My local Menards had 96″ 3/8 rods in stock.
Menards sells 8′ lengths of 3/8″ aluminum rod. See: https://www.menards.com/main/hardware/sheet-metal-rods/hillman-reg-aluminum-solid-round-rod/11276/p-1444432406795-c-9215.htm
Take two smaller pieces, using a die cut threads on it and use a coupler nut. This can also help in any adjustments.
i would like to have one just like a arrow antenna but collinear i think it would work grate i have no skills as far as antenna building so i am not even going to try lol
Wow cool antenna! I’ve seen this antenna a few places on the web and its construction plans. Is there a patent on it? If so, makes me wonder why the plans are so freely distributed. Any ideas on this?
Might just have to try and build one. TNX!
Hi!
Thank you for the complete and useful explanation of this antenna.
I’ve build this antenna with the exact measures, but from hollow rods, with outer diameter of 101mm.
I’ve modify the rods support manner, putting a rivet screw bolt in each rod. Anyway I mount the antenna above the roof of my building and connect it with a feeder line of 20 meter, 8d-fb-50 ohm coax cable. A ferrite ring is placed near the connecting point. At this point I have no SWR meter to analyze the coefficient.The antenna is working just fine with my Baofeng UV-5R, hitting most of the repeaters in the range and ensure very clear connections . It’s curious though, a more distant repeater in the UHF-band, which I open with the standard gummy-duck antenna from the same height can’t be open with this OSJ antenna after the feeder line. Any suggestions about this case?
Hi, I just got all the parts together today. It only took me about 2hours to build. You are correct the hardest part is tapping the threads on the rods. After that it all went together just fine. I test it just with outgoing SWR and it is running me 1:1.3 SWRs. Assume little antenna and really an easy Build.
A couple question.
The length of each element is given from the aluminum angle base to the tip, do I need to adjust for the length extending through and below the aluminum angle?
If I shortened the elements, drilled and thread a hole at the top, the added at brass bolt to adjust overall length. Would this allow for fine tuning?
Thank you for your time.
I built one of these antennas. I have it on a 6 1/2 ft PVC pipe inside the garage. Just for giggles, I hooked a Baofeng UV-5R and made contacts on a 440 repeater about 30 miles from my QTH. I tried another homebrew, dual band j-pole dipole, at the same height, could not even key the repeater. This one works very well. This was the best money spent for the “bang for the buck”. Thanks for the he help and instructions.
73- God bless
Allen KM4GNY
I built one, have it mounted to a 6.5 ft PVC inside the shop and can hit repearter 30+ miles away. Have not put it up any higher, but why. I have good weather, lightning protection with it inside.
I am a new HAM and have decide to give a try for better SWR with my homemade OSJ- pole antenna. I’ve surprised that when double-lengthen the short stub( for the70cm band) up to 37 cm (about 14.5”) the SWR lowers to under 1,2 and 1,1 for the 144 Mhz band at the same time. It seems also this change has improve the reach of a particular distant local 70 cm-band repeater .
My question is – does this re-design spoils the hall performance of this antenna regardless of the low SWR ?
I made one and I have 1.0 swr on 146 and 2.7 on 440,can you help?
Hi, Manuel!
When I constructed this antenna, I measured similar SWR readings. Then I experimented with a longer, near double sized short stub (for 440 Mhz). This made the SWR much better. But I can’t prove that it radiates better. Somewhere I’ve read about this antenna, originally made successfully for 144 Mhz with two stubs only, is a compromise for 440 with the third stub. Anyway, you can try my experiment for yourself and test it.
LZ1MFA
For me, this antenna transmits great but I don’t receive very well. I’ve been able to hit my 3 friends in the next town over (about 6 miles away) with fair clarity (there’s also a hill in-between), using my little Baofeng UV5R. However, I can’t receive any of their signals at all. Two of them are using the very common home-built copper J-Pole, one on a UV5R, the other on a Yaesu HT. I also can’t receive my other friend who is on a Yaesu mobile (with a car roof antenna) using 60 watts tx, until he gets about a mile away.
I suspect the problem is the wide receiver front end in the radio. The radio is being desensitized by the greater amount of non amateur radio signals being sent to the radio by the antenna. I had thist problem with a different antenna and resolved it by adding a filter that blocked the commercial FM band, 88 to 108 MHz. The filter was intended for received only operation but is seems to survive low power transmitting from a hand held radio.
Question:
I noticed in the first drawing it is indicated 1-1/2″ x 1-1/2 x 3/16″ angle aluminum is used at the top of the page under “Materials Needed”. Yet in the “parts list” at the bottom of this drawing, it is indicated 1-1/2″ x 1-1/2″ x 1/8″ angle aluminum is specified. Which thickness is used? I noticed in the video 3/16″ is used. Or does it make any difference?
Use the stronger one
I used a smaller size angle aluminum. Since it is just supporting the piece, I don’t think it matters too much. I didn’t have any trouble threading the rod. I did bevel the end first though, to help it get started. Maybe try that?
Yes
Another Question:
I mananged to thread the rods with 3/8-16 NC treads. But, I am having difficulty treading the 3/8 -24 NF thread for the SO-239 adapter. How did you manage to thread the rod with a find tread die?
I’ve use oil, cutting oil, grease, WD40 and none of it seems to help.
You do not have to tred the bracket,just drill holes to fit
You might need a die guide/holder when cutting fine tread like tpi24,
check out youtube
https://youtu.be/4LeoleetzMM
I have used this type of adaptor and its easy to cut a good tread with it – you get a near perfect read every time.
I had to reduce the diameter of the rod where I was going to thread it and also taper the very end so I could get the die started.. i used a belt sander and rotated the aluminum rod as I sanded material off. You want to make sure you are keeping the rod round as you sand. For the longer piece I rotated it by hand, but for the shorter pieces you can chuck them in a drill and rotate them with the drill as you sand the end to slightly reduce the diameter.
can you please email me the details, construction, calculation of the open stub open jpole dual band.. i have search the internet for the correct calculation but found none or maybe i just can’t find one.. i want to build my own for a 140 to 150 Mhz.. could that be possible?
Thanks for taking the time to publish this and the video!!
I built one, but found the SWR and the impedance to be pretty poor on both bands. I built a second version with longer rods, threaded the bracket, then twist the rods to tune them and lock with nuts when better. I threaded the top of the “driven” element and use a coupler to tune it.
A few observations, the UHF element performs very well once lengthened. 1.1 – 1.3 across the band. The VHF, despite all of my efforts never gets under 1.3 and the impedance is 35 – 75 ohms. Very unstable. When the “driven” element was extended all the way, the resonate frequency was obviously off, but, the SWR was 1.0 – 1.2 across a very large area with impedance in the 50’s for all of it.
So, with that, do you think the velocity factor of my particular batch of aluminum is changing the dynamics of this design? I was thinking about cutting a long groove instead of a hole for one or all of the elements so they could be adjusted side to as well as the length adjusted. Do you think this would help?
FYI, I’m using a MFJ-269 with both UHF and VHF capabilities.
Thanks again!
Note: Some of the MFJ 269 Analyzers don’t work right. – – (eHam reviews on the MFJ269) – – The MJF 259B works Great.
Example from eHam Reviews
I have had my MFJ269 for about 5 years. It works ok. On VHF and HF it is dead on. But on UHF I do not trust it. I also have a Bird and I compared several antennas tuned with the MFJ269 and the Bird and the MFJ269 was wrong everytime on the UHF side. I killed one UHF final when I relied on the MFJ269 for tuning. This antenna was checked with the Bird after the finals died and was found to have an SWR of 5:1+. Yet when checked with the MFJ269 it showed fine. I now use the Bird for everything but HF tuning. The MFJ269 still seems to work ok in this range and is nice for tuning my Buddy Pole for portable ops. It will never see VHF or UHF antennas again.
HI..
i am a radio enthusiast and had built some antennas but not an OSJ.
i want to build a single band OSJ with frequency of 143MGHz. Can i use a hollow anodized (38/ or 1/2) element? solid aluminum is rarely found in our place also with the SO239. Can i fabricate it? Can someone give me any drawing of it? thank you..
I Just made one. Single band for to meter
i mean for 2 meter band. sorry
I need a Tri-Band version 144mhz/222mhz/440mhz. I just got the new Btech UV2501 + 220 and a Tri-Band version of the ant would work just fine.
Tks Ralph K1KOB
I have all of the parts cut, rods threaded, and the angle has 1/8″ pilot holes in it. I’m waiting for a “Q” size bit for tapping the holes in the angle.
Someone asked about sourcing the material. I used OnlineMetals.Com. The shortest piece was ordered random length but I tried their custom length ability with the two longer pieces. They did a great job. Cutting the aluminum rod is not hard to do, I just wanted to test their custom ordering accuracy. It was spot on and the same cost as the random length material.
American Radio Supply has the fitting (and it looks like they used the “design sheet” from this website to advertise the fitting.
73
NE5U
Mike
I used to be an engineering technician for Collins Radio, in the avionics division. One day my boss wanted to find out how well the various antennas worked, that is, the antennas that people used with our VHF comm radios (just below our 2m ham band). We x-rayed them, to see what kind of actual antenna aero-dynamic shape they were in, and then I made up a mock airframe fuselage. Then I mounted each one of them onto this aluminum shape, and proceeded to take measurements every 15 degrees around in a circle. I used a pretty expensive “field strength meter” (it was a vector phase meter / S-parameter test set) but I was able to make an azimuth plot for each of the antennas.
This was before the days of modeling antennas on a home PC, and I bet that if I could have modeled each of these, he still would have told me to measure it. He was one who believed that well-known quip, that “In theory, theory and practice are the same. In practice, they’re not.”
My point is, I suppose, that when hams are talking about which kind of antenna is better, I would really like to see the field strength measurements that he made, otherwise we are simply discussing software models, not antennas. And I don’t mean SWR measurements either. That’s important once you build and use the antenna, but for “gain over a reference antenna” which is what we are talking about here, let’s see some real numbers, OK?
Or not. But if not, then say so. And you might also volunteer to say why you never bothered to measure it. I was a 20-year-old know-it-all at the time, and if I could do it, then you can too. You might even learn something.
73,
Jeff
I am a new Ham and just beginning to build this type of antenna. But I am struggling with the cutting the threads on the 3/8″ rod with my tap/die set.
What brand is your tap/die set?
The one I got is older set and the 3/8-24 die is too small for the aluminum rod. The rod measures about .3880 instead of .375.
Help! Infinite SWR on UHF…
I purchased one if these recently from a swap meet. The measurements are dead on. Checked for shorts, opens, etc.
I’m using it with a dual-band 5W HT. I have pretty much 1:1 SWR on VHF but on UHF, it pegs my meter, (I have one of those meters you don’t calibrate…it has two needles, forward power and reflected power). For one thing, on UHF it shows the HT is putting out 20 watts. Secondly, the SWR needle is pegged all the way to the left.
Again, I’ve checked the dimensions, etc. It’s a very nice build! Any ideas where/what to look for? It’ll be a major disappointment if I can’t use it on UHF.
Did you put a choke balun just before the feed point of the antenna. It almost sounds like you have RF traveling down the shield. If you have the extra feed line, wrap a tight coil about 6 ti 7 turns, at 4 to 5 inches in diameter.
Dennis V
WA6ATI
I have the same problem but with the VHF too. Great reception, but terrible transmission. Added 5 coils at 5.5″ for a balun, but made no differece. Tried with 100′ RG8X cable and short RG58 cable, but also made no difference, still infinite SWR.
I have trouble finding the SM1 SO239 connector here in INDIA and the shipping cost is too high to be shipped to india from US. is there any way to use other connectors for the same job ? Can the so239 panel mount flange be used for the work ?
Another question
In the design the angle is the ground and the radiating element is directly connected to the centre of the so239 connector rite ? Please help
I tried building one but not the dual band type made by the Arrow. What was I constructed is an OSJ for 2 meter band only and it works really good. The Rx and Tx were amazing! Using this antenna 10 ft above the gound connected to my 4 watts Baofeng uv-5re I hit a repeater 7 miles away from QTH and the other station commented that my TX is loud and clear. I switched to Simplex mode and he said its loud and clear in an steady 1 bar on his uv-5r using a F23 Diamond antenna.
I dont have an antenna analyzer so I was just relying on the measurements of this antenna I made.
I used 3/8 aluminum tube 58 in. on the radiating element and 19 1/2 in. the tuning stub. I wrapped with an electrical tape the other end of the 1/4 wave tuning stub for isolation and inserted both to 1 inch aluminum square bar. I put SO239 to the tuning stub bottom.
It outperforms my Jpole and Slimjim!!!
Hi, I made myself this antenna using Plans for Dual Band J-Pole 2 on your website. I used a 10 mm diameter aluminum rod. I supplied the SO-239 to 3/8 connector and prepared the project with the most precise measurements, assembled and using Yaesu Ft2d handheld radio and Surecom swr-pwr meter. I set it to swr 1: 1.0 at 145,000 MHz. For 420,000 MHz, I set it to 1: 1.09 and smaller. I have made the antenna usable by using a 3 meter long aluminum frame profile directly. So far, no problem. When I connected the same month to my Yaesu Ftm 400d radio and made 20 watts and 50 watts of tx, I saw the swr rate increase. I’ve reviewed the project many times because I have a place I missed. But I couldn’t find a solution. Do you have any advice for me? thank you. TA5LVC, Veysal, Turkey, (https://www.qrz.com/db/TA5LVC)
Veysal, Not sure what could be wrong. I’ve seen other hams use 10mm without issue. I would double check your dimensions and make sure everything is tight. Also make sure your coax is good as well. It looks good on your QRZ page. Its be wide banded so SWR shouldn’t really be an issue. Good luck, keep us updated.
I think the problem was with the adjustable size of the J pole dual antenna. Everything seems normal these days. TA5LVC, Veysal, Turkey
Hope this forum is still active. I am building this antenna and so far it doesn’t seem to be a problem. I have one question. If I use the 2 inch angle I have on hand as opposed to the 1.5 inch called for, will that affect the lengths of the elements?
Stu Metcalfe VE6SBM, Canada
Does this need a 5 round 5″ loop of cable before the attachment? Excuse my ignorance, but others similar antennas have had this.
Anyone find a source for the SO-239 stud that is rated for 446MHz. I’ve only come across ones that are good up to 300 MHz? I can tune the VHF to 1.01:1 But not the UHF side. Using 40ft LMR240
I built in the vicinity of 200 of these antennas but I didn’t see your version before we constructed them. As I live in VK7 we have the metric materials here and I used mainly 10mm rod threaded 10×1.25mm and an entirely different feed adaptor that we manufactured and this made the antenna flexible to fit either SO239 socket or N type socket. That was many years ago and since then we made more antennas using the same adaptor that you have or the chinese equiv. We found we could use 12mm x 1mm tubing and tap the tube 10 x 1.25mm and use 10mm threaded SS as mounting threads for the passive rods with a nut either side of the angle for each tube. The radiator tube is tapped 3/8 24 and fitted to the feed adaptor. We have used 40mm x 40mm x 6mm angle for the bracket which is much more rigid. Performance and swr is very similar.
I am starting to build this antenna, but I do not have any 1.5″ aluminum angle. I do have 1.5″ stainless steel angle. Would replacing the 1.5″ angle with 1″ angle effect the lengths of the elements, or the spacing between the elements? Otherwise, would using stainless steel angle cause corrosion from the dissimilar metals?
I have been looking for the formula to calculate this antenna on other frequencies. Does anybody have the design info?
Hi, is it possible to drill and tap the ends of the rod rather than thread them externally? just thinking it might be easier for me to drill and tap and mount in the aluminium angle with a bolt rather than a nut top and bottom? I understand doing it this way there’ll be no adjustment on length unless i pack with washers?
Nothing wrong with drilling and tapping the ends. Typically if done correctly you shouldn’t have to adjust as it’s wide banded. If it’s a major concern, you can always leave the elements longer and cut them down to obtain optimal SWR.
Thank you for this article. I have built one of these and am very happy with it. I put together a shopping list using Menards for the hardware and a W5SWL’s ebay store for the connector here:
https://docs.google.com/spreadsheets/d/13H_xbqCW8KLHeurG8OLnVWGCj-q7jtL6tp2ab3-5oOE/edit?usp=sharing
The price per antenna come down to $34. each if you get a group of six builders.
I used 3/8-16 threads and nuts on the two resonating poles as 3/8-24 nuts were expensive in my location. It works fine, but if I were doing it again, I would just drill a 3/8 hole through the angle iron instead of threading them. The 16 pitch thread adds a bit of an angle when screwing the poles in. You can simply tighten down the nuts on both sides to keep it in position. It would probably be better to use 3/8-24 thread and nuts as the instructions show.
Thank you and 73,
Alex W9LEX
Took a chance and went completely simple with no special parts and it all worked as long as the spacing and lengths were the same. Used stainless steel threaded rod instead of aluminum since I wasn’t worried about weight – very close diameter. This meant not tapping needed. Also used stainless steel angle iron so not problems with different kinds of metals. Hard to find the “special” connector, so used SO-239 mounted on the “other” side of the angle iron right next to the 19.25″ rod, with .25 incd copper wire from center conducter to 19.25 fed element. Insulated that from angle iron with very short piece of PVC around pipe and 2 teflon washers top and bottom side. Wrapped 2 layers of teflon tape around that part of 19.25″ threaded rod. Worked great at first assembly with highest SWR on any band 1.5:1. Thanks MUCH for the clear instructions. OM1US
I purchased 3/8 aluminum rod at Home Depot. Tried to thread it using 3/8-24 die. It did not work. Rod is really 10mm even though sold as 3/8.
Used 10 mm die and 10 mm nuts. SWR less than 1.2 for both 2 meter and 70 cm bands