Howard,

several days ago you asked if one of us could describe a J Pole antenna to
you in enough detail so you could build one.  Well, I will try.  Here it
goes...


construction for a 2 meter J Pole :

First, imagine the print letter J . This represents the shape of the
antenna. It has one long side and one short side all connected at the
bottom or said another way, one continuous length of conductor shaped into
a J.

Now turn or flip the J backwards as if you were writing it with the short
side on the right rather than on the left.  I say this simply because this
is the way it is usually shown in the ham mags and on most web pages.

The J is one single "conductor" in the shape of a J.
From the top of the long side of the J to the bottom, for 2 meters, is
about 58 inches long before it turns horizontally a couple of inches and
then goes vertical for about 19 1/4 inches. So you have a total length of
about 77 1/4 inches forming a single J shape.

The center conductor of the coaxial feedline is attached to The long
section of the J Pole and the braid or shield of the feedline is attached
to the short section.  These feed points for the coax are spaced up from
the bottom of the J or antenna about two inches, and they need to be,
initially, adjustable , until you find the optimum tap or feedpoint that
gives minimum SWR. So, do not make a permanent feedline connection yet.
Once you have these feedpoints adjusted to produce minimum SWR, you can
solder them for a permanent connection.

Again, the shield of the 50 ohm coax is attached to the short section about
2 inches up from the bottom.
The center conductor of the 50 ohm coax is attached to the long section
about 2 inches up from the bottom. Both the center conductor and the shield
should now be side by side on the vertical elements equal distance from the
bottom. One on one vertical side and the other on the other vertical side.
BOTH are connected equal distance from the bottom of the antenna and are
adjusted up or down equally for lowest swr. This is the tricky part. Some
method of making temporary connections for tuning will be needed or they
can just be tack soldered for testing and tuning. 

For tuning, you can mount the J Pole on top of a short pole, a length of
PVC, a push-pole, etc., or you can mount it on a temporary support like a
wooden ladder.

Then, once you have it tuned, you will need some method of mounting the
antenna to a mast, pole, etc in your final installation.

Most builders just add about 15 to 20 inches to the long side at the bottom
for mounting.
This extra length becomes invisible to the operation of the antenna; thus,
not effecting its operation.  So, it can be metal tubing for a J pole.
Adding this length would make the long side about 58 plus 15 inches = 73
inches...or
58 plus 20 inches = 78 inches.
 
Of course, you want to mount the antenna in a location about 1/2 wave
length away from any metal surface near the antenna in any direction except
the bottom of the antenna.

 The lengths and spacing of the J element is not very critical due to the
variable tuning section. The main thing is to get the final swr down as low
as possible.

Also, it is recommended to add about 4 or 5 turns of coax in a neat coil
with coils side by side at the bottom of the antenna making an air choke�
out of it to keep stray rf off of the coax outer conductor.

It is a challenge to describe something like this, but there you have it.
I hope you are able to visualize it well enough to take a shot at actually
building one.  Alternatively, they are available to purchase either fully
assembled or the parts that you can put together yourself.  

Ron, AC4HM