On Oct 12, 7:02*pm, Owen Duffy wrote:
"Peter" wrote :

I can't see that it makes much difference, but is there any deference
which way the coax is connected to a J pole antenna. Is it better to
have the centre of the coax connected to the main element or the stub?
I notice that most if not all J pole designs on the net have the
centre of the coax connected to the main element, however when I refer
to a 1977 ARRL antenna book it has it connected the other way.

Is there any difference?

It is doubtful that one is better than the other, though the various
proponents are usually adamant that there is only one 'correct' way.

A better method is to feed the coax inside the tube at the centre /
bottom of the U section, and have it emerge at the feedpoint where you
bond the shield to tube at the emergence, and take the centre conductor
directly to the other side and connect it. Not as adjustable, but this
method incorporates a balun.

You can get nearly the same effect by strapping the coax to the outside
of the tube and bonding the shield at the bottom of the U section (as
well as at the 'feed point' of course)... but no one seems to do it. Not
surprising, as it is a measure to reduce common mode current which most J
pole devotees pretend does not exist.

Owen

Owen
Every set of instructions I found when I was building my collinear J-
pole included a BalUn in the design. Some of the users of these
antennas are not fanatics but simply find it easier to use six turns
of coax as the the BalUn. And as to why it is simply easier to
apply. Since I am getting to the place were I don't like the
inelegance of the coax BalUn I will soon be changing over to a ferrite
bead BalUn for the sake of it's lesser ice collecting properties, it's
improved appearance, and smaller visual profile. Not everyone
believes that the antenna that they are using is magic. Many have
other reasons for not doing it in a particular way. Other than the No
BalUn voodoo are there other reasons that you don't like J-poles?
--
Tom Horne, W3TDH