0 Members and 1 Guest are viewing this topic.
CORE TYPE CURRENT BALUNHighly recommended. This is a very low loss balun and ideal for use with a tuner.This balun works by controlling currents. THERE IS NO TRANSFORMER ACTION. The two windings must be in the same sense (dots at the same end). The magnetic fields of opposing balanced working currents will cancel each other out and so present very little impedance (other than the resistance of the wires) to these currents. On the other hand, common mode currents will produce a mutually inductive magnetic field and face a high impedance.This means the more turns the better, up to a point. In this case, the windings are a transmission line that has losses but these are much lower than the losses transfering energy from one winding to another through a core.Design considerations are really very minimal. Since the losses of balanced lines are low compared to coax, you aren't losing much except for the resistance of the wires which is very low compared to radiating resistance anyway.The current balun shown here, wound around a steel bolt, is probably a little crude but why not? Steel or iron is not normally used for RF because there are too many eddys making it too inefficient for transformers. In this application, since there is no magnetic effect for the desired currents, it doesn't matter. For common mode currents on the other hand, inefficiency is an advantage. Not only is a high impedance presented to common mode currents, the energy from them is absorbed by the bolt.