Not quite. Look closer - http://www.arrowantennas.com/j-pole.html
You assume it should result in common-mode currents.
And you know what happens when you Ass u me.

But....Common mode current on the feedline can't be avoided
no matter how the antenna is fed. I agree that the antenna is
quite usable without decoupling, and I've found that the 1/2 WL
ringo's usual "gamma loop" feed is also fairly good as far as that.
But there is no way to totally avoid all currents, without some form
of decoupling. If you believe you can, try some tests adding decoupling
sections. If you don't see an increase in performance, I would
be *very* surprised. In some cases, it's possible for the currents
to add, and produce a gain at low angles, but it's fairly unlikely.
Most of the time, the pattern is skewed upwards. It takes at least
two decoupling sections to fully decouple an elevated vertical.
To me, you have none, although maybe you could argue that your
feed of feeding qualifies as a first decoupling section...Lets say
you win, and this is the case...You still need one more, if you
want to be fully decoupled... If you believe you are now, I'd be
willing to bet you are deluding yourself.
Thats not to say the antenna doesn't work ok as is...I'm sure it
probably does, except the most retentive of users...I've used
loads of halfwaves with no decoupling...But those were all on 10m,
where it's not so critical. BTW...The results of adding decoupling
sections will vary from user to user, depending on their lines.
But if the antenna is totally decoupled, the amount of current will
be the appx same for any user, no matter feed length.
When I say total, I mean as much as practical. I don't believe you
can totally eliminate all current. There will always be a small
amount.
I doubt I would change the antenna....Would make it cost more...
I'd consider a super deluxe version for a higher price, if they wanted
full 2 section decoupling...:/ And if I went that far, I'd use a dual
5/8 design to get more gain. You'd be reinventing the isopole...:/
MK