Many store-bought G5RV antennas come with the balun already attached 
at the end of the twin lead.

Most of the others tell you to simply roll about 15 turns of the coax 
into a coil with an 8 or 10 inch diameter at the point where the coax 
attaches to the 300 ohm or 450 ohm line.

In that case, "building the balun" is as simple as making the coil of 
coax, and wrapping it up with cable ties and tape so that it stays 
coiled.

In other words, if you can count to 15, and gestimate a circle with an 
8 to 10 inch diameter, you can build the balun by using part of the 
100 feet of coax that is the feed line.

As for the MFJ doublet, I suspect they recommend a 4 to 1 balun.

The general tendency is to use a 4 to 1 balun with a doublet that is 
fed with 450 ohm ladder line. However, if you want some interesting 
reading as to why a 4 to 1 balun and 450 ohm line are not always the 
best choices, go to dx engineering .com, open their wire antennas 
page, and read their article about choosing the best balun.

It is an info-mercial of sorts for their doublet and their balun, but 
what they say makes plenty of sense, and reads well with speech.


Mike Duke, K5XU
American Council of Blind Radio Amateurs