Why Open Wire Fed Dipoles Need To Be Balanced

It is important, if you’re using a dipole antenna fed with open wire line feeders, to try and keep the antenna balanced. The first rule is to make sure both sides of the antenna are the same physical length. Sometimes, even when doing that, the antenna will not be balanced due to the asymmetrical issue. If one end of the antenna is not the same distance above ground as the opposite side, that may cause an electrical imbalance. Objects that are close to the antenna can cause some imbalance. Some of this we have control of and some of these physical issues causing an imbalance we have no control over. First off, make sure you have the same amount of wire each side of the center insulator.

In a well designed open wire line fed antenna that is balanced, the feedline will not radiate! The open wire line feedline, should not radiate! When the antenna is balanced, the current in each leg of the feedline will be equal, but 180 degrees out of phase. It’s the equal amplitude and 180 degrees out of phase that keeps the feedline from radiating. Feedline radiation in or near the shack can cause all sorts of issues, including RF in the audio of your HF rig. In a smaller way, it will cause the radiation pattern of the antenna to deviate from the text book model due to feedline radiation, although, that in my eyes is no big deal.

One comment

  1. I like seeing write ups like this one. Not sure who the author is but I will guess and say either Joe or Chuck. It was Joe W3GMS who convinced me to use ladder line. (At least for 60 meter to 160 meter) Anyway since then I had built a home brew ladder line feed line from the rig to the tuner. I have also built a balance tuner and it’s not likely I will go back to coax for a multi band antenna again. The tuner was built so that the roller inductors would use one gear assy/crank handle to turn the inductors together. I have now gather new parts to build another tuner, but in this one, the roller inductors will have their own individual gear assy/crank handle for each individual roller inductor. Why one may ask? For the reason mentioned in the this article about the antenna height on one side may be higher or lower and in case the antenna or the ladder line may be longer or shorter on one side. Having the capability to Tune To Balance the antenna by means of individual inductors while watching two individual ammeter inline to achieve the same current on both sides of the ladder-line. This will also achieve confidence in your antenna system! Again I have to give credit to Joe, W3GMS on teaching me these practices.
    Thank you Joe.
    Ken WB4AM

    Like

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