Topband: Choke baluns

[Larry Molitor]

There is NO reason to use choke baluns, coils of coax, or ferrite cores on coax when feeding a RX antenna. Beverages, Flags, Pennants, K9AY's, EWE's, all have the same requirement, although the purists may elect to consider the actual feedpoint 
 impedances enough different to be significant.

All anybody needs is the proper matching transformer properly installed at the feed point. The proper matcing transformer is wound on a binocular core. Examples are shown in ON4UN 4th edition, W8JI's web page and my web page (under rotatable Flag topic). Using a so called "UN-UN" is the very worst thing you can do to a RX antenna. You might just as well run your coax over to the nearest power pole and hook up to the ground wire.

The winding to winding capacitance of a properly constructed isolation type transformer averages 5 pF depending on wire size and number of turns. For those of you that can't or won't do the math, this is equal to about 17,000 ohms at 1.8 MHz. That's a whole lot more than you can get from any magical arrangement of toroids and coax.

Use the proper transformer and isolate your grounds and your RX antenna will work as well as possible in the environment it's installed in.

Larry - W7IUV
DN07dg - central WA
http://w7iuv.com