OCF Masters have spent years designing, building and writing about Off-Center-Fed Dipole Antennas.Through that time, we have used many different commercial and home-brewed baluns for our antennas.We learned a great deal about the idiosyncrasies of OCFs and the Baluns needed to make them work properly.
To start, OCF antennas are by their nature unbalanced making them particularly prone to common mode current, which causes feedline radiation. In fact, the Carolina Windom uses the feedline as part of the antenna providing some vertical radiation.This feedline radiation is then stopped from causing chaos in the shack by placing a 1:1 Current Balun 25 feet down the coax leaving a 25-foot vertical element as part of the antenna.
But, OCF antennas are tuned for proper resonances with no feedline radiation. For proper operation, the feed line radiation must be blocked at the source, the conjunction of the radiating wires and the coax feed line.
This is accomplished by using the combination of a Guanella 4:1 Balun and a robust 1:1 Current Balun/Choke properly isolated to minimized coupling of the two cores.Through our testing we found that many commercial baluns are lacking sufficient choking. Insufficient choking causes feedline radiation on the antenna’s lower frequency bands, which lowers their resonant frequencies.
Our kits have the difficult to find components needed to make an excellent balun for OCF antennas.