When I got started with ham radio I only used hand held radios but I soon wanted a bigger radio to act as a base station at my home. As I was looking at antenna’s online and seeing the prices a friend suggested I build my own J-pole. So I started researching them and I feel in love with the idea.
How Do J-poles Work
J-poles are neat. They look interesting and they don’t need to be grounded. I’m not sure I can really explain them very well. But basically the short side of the J and the long side of the J react with each other electromagnetically like a transmission line. Then the magnetic waves are broadcast out the top half of the long J as radio waves.
The length and spacing of the elements of a j-pole determine the frequency range it resonates with. Most people make them for the 2-meter or 70-centimeter bands.
I found this video helpful when I was trying to understand them.
Is a J-pole Antenna Directional
No they are not directional. But there when looking at radiation pattern simulations online they are not exactly the same all the way around. So I suspect there might be a very small directional property to them. But this is beyond my knowledge level at this point so I’ll leave you to research that more.
Building a J-pole Antenna
The first thing you need to do is figure out what frequency you want to use the j-pole on. This will determine how you build it. I looked up a j-pole calculator and tuned mine to 146Mhz. The site I used seems to be down but they are easy to find. Like this one.
Getting the Parts
As a side note I picked up Type L copper pipe. It’s a bit thicker then Type M so I thought it might hold up better outside.
Putting it together
The first thing I did was cut out some scrap wood to the size that the spacing needed to be between the pipes. This way I could solder everything together without worrying about anything slipping out of place.
Next I had to attach the wires. This is were the hose clamps come in. The wires need to be attached at the right spot in order to get good performance. With the hose clamps I can test and change the attach point if needed. Refer to your j-pole calculator results to figure out how far up the wires need to be attached.
The core or center of the coaxial cable attaches to the long pipe. The shielding of the coaxial cable attaches to the short pipe.
I hooked up a radio to it and it worked very good for receiving. But I need to test the SWR before I try to broadcast anything.
Testing the SWR
I’m proud to say the J-Pole SWR was low and everything seem to be really good without me having to make any changes! I’ve also been told over the radio that it sounds very good.
A side note: It’s not show in my images but when you hook your cable to your j-pole it is recommended to loop it 4-5 times in a 4 inch diameter circle. This acts as a RF choke or balun near the feed point. You can also use ferrite beads if your cable is too stiff to loop. The purpose is the limit the amount of energy coming back down the line into the radio when broadcasting thus increasing your SWR and limiting sensitivity.
The next thing I want to do is replace the hose clamps with a SO-239 hook up. I think that would look a lot nicer and I can attempt to water proof it. But for now it works really well and it was a lot cheaper and more fun to build then buying a premade antenna.