J-pole Antenna

J-Pole Antenna

J-pole Antenna - Everybody says keep one in your bag, nobody seems to make one work right. Here's the straight scoop on WHY the J-pole is NOT an easy antenna to duplicate! Just to make my position on the J-pole clear, I hate them. I don't use them. I don't make them.

I don't like antennas that are difficult to duplicate (see my dipole, it's easy). The J-pole has so many variations on the web that I'm not going to link to any of them. Even the twinlead dipole from ARRL has been questioned.

So you wonder why I bother with this. It's because of the easy portability of the twinlead version of the J-pole and it's recommended use by some ARES groups.

Henry - KM4O (sk) and I spent a couple of hours looking over the different antennas on the web and seeing so many variations decided that we were just going to have to build one that the group could duplicate. Now I'm not selling this as a good antenna, or an antenna for you to duplicate. Rather it is just the product of our efforts to make one work for the ARES Ready Bag.

Below are the dimensions we came up with using the Radio Shack twinlead. We experimented with the length of the antenna as well as the position of the feedline connection point. We achieved a SWR of 1.7:1 at the operating frequency of 146.625 MHz and didn't see a wide variation from that plus or minus 1 MHz. The antenna seemed to perform okay so it wasn't just a matched dummy load.

Have fun if you choose to make one of these. If you come up with one that REALLY works, please make one for me!

73,

Tony - W4ZT (ex WA4UPE) and Henry - KM4O

Gary O'Neil, N3GO, sent me an email with a wealth of info on the J-pole antenna design. He may have the answer on a usable j-pole. You can find his info at http://snow.prohosting.com/~w0rcy/Jpole/jpole.html

This is a simplified diagram of the J-pole. on the bottom end (right in this picture) the two conductors of the twinlead are twisted together and soldered. See the photo below.

The connection point of the coax on the twinlead was found experimentally. We just stripped the insulation off of the side of the twinlead and moved our coax connection point until it made us happy.

Here you can see the coax connection point covered with heat shrink tubing and you can also see the 1/4 inch notch in the twinlead.

This is the completed J-pole with about ten feet of coax attached.

Last update March 28, 2005