Saturday, October 5, 2013

W8JK Antenna

The W8JK antenna design is a clever beast. Invented by Dr. John D. Kraus, W8JK, in 1937, it uses two dipoles, both driven and out of phase with each other, to create a directional antenna (no front to back ratio, though) that works on six bands (20-17-15-12-10-6 meters) and as a top loaded vertical on 40 meters (with a counterpoise ground). I used one of these at two locations and had excellent luck with it. The wire beam version, as shown in the top photo, is the cheap method (which I used) and you generally pick the direction that you want to work, which in WA is towards Europe, of course. In real practice it straddles the house so mine always pointed north-south and north over the pole to Europe worked for me. You need a balanced antenna tuner with this antenna and open wire or a low loss twinlead feedline. Here is a good article on the W8JK antenna by ZR6TXA. Dr John D. Kraus was an amazing physicist, inventing antennas for radio astronomy, building cyclotrons and working on anti-radar measures and ship de-gaussing during WWII.

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