Tom Horne wrote in
:

....
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?

It is not that I "don't like J-Poles", but that they have certain
characteristics that should be considered in their design and
implementation.

They are an 'end fed' antenna, and there is necessarily some common mode
current excited on the feed line / supporting mast structure. A balun
helps to reduce that, and I described an integrated balun that is an
elegant construction, though a further ferrite current mode choke would
be of benefit.

The plumber's delight construction which is often hailed as an advantage
is actually a frustration when trying to reduce common mode current.

Though the J-Pole is often promoted as a easy thing to implement, they
figure disproportionately in online forums with questions like "I
adjusted my SWR real good in the shop, and when I raise the thing, the
SWR changes". The common sensitivity of measured SWR to antenna position
and line placement is a sure sign of high common mode current.

The common mode current doesn't necessarily stop them working, but it
does frustrate setup, a trap for the inexperienced.

BTW, J-Poles are not popular commercially in this country, I cannot
recall ever seeing a commercial J-Pole for non-amateur use. Perhaps there
is a message there about convenience and predictability for the
installers.

If a J-Pole suits your requirement, go for it. They warrant an effective
common mode choke, if for no other reason than to make VSWR less
dependent on the layout below the feed point.

Owen