VHF J-Pole
Tried to build a 146MHz J-Pole using wire, following some of the online guides. It seems simple enough: stick a half wavelength vertical on top of a quarter wavelength matching section. The ends of the matching section have very high impedence, while the bottom is very low. So, somewhere on that path is 50 Ohms. I must admit my ability to construct isn’t the best, so the joints and connections are probably shoddy at best. Ended up using a 150 cm jumper coax bought from a local supplier. Cut one end off and connected alligator clips, one to the braid, one to the center conductor. Made few loops of coax about 4 cm in diameter as an RF choke. Alas, I’ve been told I have a hum in my transmission. Not having an antenna analyser for VHF, I can’t *really* tell where the 50 Ohm feed point should be, but even just a few millimeters off shouldn’t add a hum. I’m a bit baffled. I guess the best explanation is not enough RF choking, and the microphone or IF stage in the radio are picking up a bit of stray RF. Next will be to add a ferrous material to try and increase this.
Eventually, I hope to build a larger J-Pole for 14MHz. This isn’t a very conventional antenna, but will be the easiest for our situation. Having access to a large tree will allow me to put the ~15 meter tall antenna up rather high. It will have a feedpoint close to the shack, at the bottom of the tree. Best of all, it won’t require a huge amount of radials to get a bit of low-take off radiation happening. Hopefully this will work for a bit of DX on 14MHz.