The J-Antenna is an end-fed 1/2 wave with a 1/4 wave matching section.
The bottom is tied together forming a "hairpin". The coax is moved up
from the bottom to reach the 50 ohm point and secured. The feedpoint is
actually balanced so there can be some issues feeding the antenna with
coax, which is by design is unbalanced. As a matter of convention, the
shield is tied to the short piece and the center conductor is tied to
the long side.
The matching section does not do much radiating because the signals are
cancelled out, leaving the 1/2 wave section in the clear to do the
radiating as vertical dipole. This antenna does have some gain
associated with it over a ground plane antenna and it is a great way to
start an argument. The nice thing about the J is that you do not need a
ground or ground plane to work against.
Ray Wells wrote:
Jason Winningham wrote:
On Jul 1, 2007, at 7:59 AM, Richard Polivka, N6NKO wrote:
I have just now created a vertical 1/2 wave dipole. I tune it with
an MFJ box.
A roll-up J-pole is slightly more complex to build (but not much!)
and doesn't need a tuner. A J-pole has noticeably more gain than a
dipole, too.
-Jason
kg4wsv
Given that a J-pole is only a dipole with an alternative feed method
(i.e. at the end rather than the centre), I have to wonder where this
gain comes from.
Ray vk2tv
_______________________________________________
Xastir mailing list
Xastir@xastir.org
http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
_______________________________________________
Xastir mailing list
Xastir@xastir.org
http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
