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.
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
Here are some SWR Shots. I don’t have state of the art equipment so this will do for now
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.
EDIT (5/2/11): I’ve Also built a “Adjustable” version of the Open Stub ( OSJ ) J-Pole as seen HERE.
EDIT (10/20/2011): Someone let me use a MFJ Antenna analyzer so here is a reading from the VHF side of the Antenna.
@ 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.
Here is another reading on the VHF side of the antenna
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.
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.
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.
F6KCZ’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.