Post by s***@hotmail.comSo, if coax is kept inside the tubing, there is no stray rf and
therefore a choke or balun is not needed?
Gary did a good job of answering your questions, but I am reinforcing what
he said.
By design, the J-Pole may allow feedline radiation: None, a little, or a
lot, depending on the users unique configurations of feedline length, design
frequency, and accuracy of matching-stub construction, etc. Therefore an
isolating 1:1 Balun or coils of feedline (choke) at the feedpoint of the
antenna are highly recommended. Routing the coax inside the variable lenth
of the main antenna length to get to the shorting (matching) stub would have
little or no effect on preventing feedline radiation, if your design was
subject to it in the first place.
Post by s***@hotmail.comAre you saying the shield must be grounded to a surge supressor to
prevent lightening stikes?
Not everyone is subject to lightning, and for some it is rare enough that
they choose not to worry about it. But if lightning protection design is
used, it requires shield-grounding. Coax shield (braid, solid, any kind)
must be grounded, and at several points depending on the tower height, mast,
length of feedline, etc. In order for lightning arrestors (more commonly
called SPD or Surge Protection Device) to work properly, the coax shield
must be well grounded *before* it is connected to the arrestor/surge device.
That's another whole subject and we have explained your J-pole doesn't
"need" grounding several times. A copper J-Pole however, is about as
attractive a point for lightning attachment as you could offer. It is also
subject to the same levels of static electricity that any airborne antenna
picks up. Act according to your individual desire for survival there.
Post by s***@hotmail.comMy ideas was to run the wire inside and even make the coaxle
connections inside the tubing with wire terminals and screws, so as to
keep everything neat and weath proof.
That would be a really neat and pretty wx-proof design, but a lot of work.
There might be an easier way to wx-proof it, mentioned later.
Post by s***@hotmail.comWhat if you used a non insulated pvc type pipe to connect the stub and
verticle element?
The cross-connector is a shorting, matching "bar", as Gary warned you
against using the word "stub" if that was going to confuse anyone because it
is not a waveguide or filter or anything else the word stub is normally used
to describe. Therefore it could never be made of an insulating dialectric
such as PVC. You could however hot-dip coat the whole antenna in plastic or
rubber if you wanted to really wx-proof it, and this would eliminate the
difficult inside-assembly of coax in the tubing that your proposed.
One final note: the J-Pole is no miracle antenna. It's has zero gain when
compared to any vertical antenna, and its entire attraction is it "fairly"
easy construction, and very inexpensive construction materials. To get as
*reliable* a vertical antenna for marine use that I required, might have
cost well over $100. At or above that level the vertical antennas of 5/8
wavelength can normally provide gain of 6-10 dbi, and I do not want to get
into what that is compared to as it has been hashed over a million times. I
would leave it at "there will be considerable gain possible in vertical
designs over the J-Pole". You have to be willing to pay for that. Most users
are happy with J-Pole performance so it's record stands pretty well on its
own.
73,
Jack Painter
Virginia Beach, Virginia