Last week, we wrote about how to build a 10m antenna. Today, we’re going to talk about how to build a 2m, J-pole antenna. The J-pole is a great antenna for 2m FM operation. In addition, it’s very simple to build one, too! That makes it a great choice for your first VHF antenna.
The J-pole antenna is basically an end-fed, half-wave antenna. Instead of the matching network used on HF end-fed antennas, J-pole antennas are fed via a quarter-wave matching stub. There are several good Web pages on the theory of J-pole antennas, so I’m going to leave it up to you if you really want to know how they work:
Make a portable J-pole
One way to make a J-pole is with 450-ohm ladder line, as shown in Figure 1. These plans were published by the Douglas and Elbert Counties (CO) ARES group.
Simply cut the ladder line to the dimensions shown and solder a length of 50-ohm where shown. If you have a VHF SWR meter, you can check the SWR. I’ve made several of these, though, and I’ve never had to adjust the tuning.
Not shown is how to secure the coax. What I do is to punch two small holes in one rung of the ladder. Then, I thread a tie wrap through the holes and fasten it around the coax. That provides a nice strain relief for the coax.
Use copper for base installations
The link above also has plans for a version made with copper tubing. This antenna would be a good choice for a base station. Note that the dimensions are slightly different. That’s because radio waves travel more slowly in 450-ohm ladder line than they do in copper pipe
Also note that this antenna has a coax connector. This makes it more convenient to use a pre-made coax cable for base installations. If your coax cable has a PL-259 connector, use an SO-239 connector on the antenna instead of the BNC jack.