Half Wave End Fed Tuner
Dave Ottenberg, WA2DJN
I was recently interested in long wire, half wave antennas. I went to the internet and found several web sites, with very good information on the subject. One of the web sites was from Steve Yates, AA5TB there he described several different tuners, using Polycon and standard type capacitors. He also used Toroid type coils. I decided to build a tuner and see if it would work for my idea using a long wire antenna. I checked my parts boxes and found a 100PF variable capacitor and a T50-2 Red Toroid core, a BNC connector, a Binding Post and finally a plastic box to mount the circuit. (These plastic boxes come in several different sizes from Staples and are reasonable in cost.) I put together his circuit and tried it out with 5 watts of power and tried it out with a 65 foot long wire antenna on 20 meters and 40 meters. I then changed the power over to 50 watts and it worked ok except I got an RF burn on my finger! This led me to make an insulated plastic coupling and put it on the capacitor shaft. No more RF burns!
Steve Yates suggests that you use a 4.7K resistor ½ watt from the antenna to the ground terminal in place of the antenna and see how the tuner will load up using a small RF signal less than 5 watts. This checks the tuner setting and is about the same as the antenna load. Steve also uses a three-foot wire from the rotor of the capacitor as a counterpoise for the antenna.