Very descriptive and understandable Ron.
Thanks.
Pat, K9JAUAt 07:49 PM 8/27/2012, you wrote:
>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.=20
>
>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 =3D 73
>inches...or
>58 plus 20 inches =3D 78 inches.
>=20
>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=9D
>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. =20
>
>Ron, AC4HM