I like the 75 ohm because it is a good match to the dipole. If you do
the 300 ohm line and make the driven element a folded dipole out of
the same twin lead, it will also be a good match.

Usually I have found it works well even without a good match on a
dipole because the twin lead is generally a low loss line and the
radiation from the feed line does not really reduce the usability of
the antenna.

A poor match will be inclined to generate TVI and sometime get RF back
into the shack. Also, some of the newer radios will not drive anything
other than 50 ohms.

Most likely you have a tuner or you would not be considering a
balanced line anyway.

If you go with the 75 ohm scheme and feed it directly from a "modern"
transceiver it will probably still work pretty well but it will be
likely to generate TVI.

If luck is on your side, the 300 ohm feed MIGHT work too, but not as
you intended.

Whatever you choose, start at low power & work your way up.

I cannot figure out what you said that generated so many juvenile
responses. It sounds like a reasonable question to me.

On Tue, 26 Jul 2005 15:40:38 -0400, Eric Delongchamp
wrote:





Hi !



I want to put up a 40m dipole antenna and my question is what a
transmission line to use, I have two defferent type of twin lead to
choose from, one is 75 ohm and a TV 300 ohm line. I'm using Yeasu 747
GX and MFJ 949 E for equiment. Thanks



Eric D.