New Dipole with Common-mode Choke
After doing quite a bit of research I found that my “ugly balun” wasn’t helping me very much on the bands I primarily use. I was still getting quite a bit of RF back on the shield of my coax and it was wreaking havoc with other electronics in my shack. I found G3TXQ’s blog through a video by M0MCX titled 1:1 Baluns – Myths, Facts, and Fiction which contained a ton of useful information. Using this information from G3TXQ’s site I’ve built a new dipole that will eventually be an 80/40/20m fan configuration but at this time is just has the lengths for 40m.
Using his chart below I went with the 17-turns of RG-58 on an FT240-43 ferrite toroid. According to his research this should provide over 8000 ohms of resistance to RF on the shield for the 80m, 60m, 40m, 30m, and 20m bands and >4000 ohms all the way up to 10m.
The dipole has been installed and so far all of the negative effects I was having in the shack have disappeared. It’s still a little long on 40m but weather has prevented me from tuning it. I plan to add the 80m and 20m wires in the next few weeks.
Check out his site for all the details on how he measured each toroid configuration: http://www.karinya.net/g3txq/chokes/
