balun for extended double zepp


Dan Earhart:
I have just constructed an EDZ and need the balun to coax feed from the balanced line. Can I construct one, presumably 4:1, from coax, such as a coil of coax? This seems to be one of those things done frequently in past years. Can you bring me up to date? Thanks 73

Steve Katz:
The "coil of coax" cannot create a 4:1 balun.  It's just an RF-choke type balun which helps isolate the transmission line from the antenna by choking off RF current flowing on the outer surface of the coaxial cable's outer (braid) conductor.  It provides no impedance transformation.

To make an impedance-transforming balun, one can certainly be constructed of coaxial cable, but the intended transformation will occur only at one frequency, because this is a tuned transformer (tuned by the coaxial cable length).  As such, a coaxial 4:1 balun, which can be constructed of 1/2-wavelength (in coax, using the Vf formula) connected as a phase shifting network between the balanced sides of the antenna (and not as a coil in the transmission line), is normally used for monoband yagis and such, and not for any antenna intended for multiple band operation.

A 4:1 "wideband" balun is most easily constructed of wire windings on a heavy-duty ferrite toroid core.  If you haven't made one before, great information is in the ARRL Antenna Book; Walt Maxwell's (W2DU) book on Baluns and Ununs; and other texts.  However, commercially made and readily available wideband, high-power 4:1 baluns for HF operation are also a good choice: They don't cost much and are normally weather-sealed and convenient to use.

I've used the Radioworks 4:1 baluns <>, type B4-2K, with great success.

Of course another option with an EDZ is to just bring the open-wire or ladder line directly into your antenna tuner, eliminating the need for a balun or coax altogether!

73 de Steve WB2WIK/6


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