On 11/28/2011 10:40 AM, Ralph Mowery wrote:
"Tom wrote in message
...
Can anyone direct me to the dimensions to build a six meter J-pole
that is patterned after the Arrow Antenna two meter design that had
the feed point at the bottom of one of the elements rather than at a
point part way up the height of the matching stub.

The reason that I would like to use that design is that I would like
to use Rigid Aluminum Conduit to build the antenna. There not being a
lot of simple inexpensive fittings for Conduit the way there is for
copper pipe a mechanically simpler design would be easier to build.

Replies are welcome on or off list. Let me say that I would rather
not be subjected to any tirades about the inferiority of the J-pole
approach or the superiority of some other antenna design. That does
not mean that I am not open to suggestions for a better approach as
long as it is civilly stated and I am spared the application of Rant
Mode.

--
Tom Horne, W3TDH

If you have not found anything by now, you may go here for a 2 meter
version. Then divide the 150 mhz frequency by the 50 mhz frequency and get
a number near 3. Then multiply ALL the dimensions by that number. That is
the lengths, diameter of the elements and spacing.
http://www.w4cll.com/ijpole.html


Tom,
how concerned are you about the "match"? What length of coax are you
feeding it with? Do you care if the coax radiates? What bandwidth do
you need? (fat elements have broader bandwidth, for instance). How
rugged does it need to be?

You're looking at something with an overall length around 3 meters/10 feet?


If the j-pole is being done so you have a mechanical support, there are
other ways to approach the problem. I assume you want something that is
"feedline comes out at the bottom", so why not something like a dipole
with the feedline going up inside the bottom half of the dipole? You'd
need something mechanically strong enough to hold the two pieces of
aluminum together that's an insulator. Hose clamps would work to both
make the wiring connection and hold the tubing to the insulator. (I'd
look at a piece of fiberglass or plastic rod of appropriate diameter.)
Since you want to use conduit kinds of things, what about using standard
plastic electrical things. Perhaps a plastic conduit outlet body?
(Cantex PVC conduit body, type C, 1/2" hub, Grainger part #4FYP5, about $5)

Just screw the threaded end of the conduit into the body and you're
done. (If you get the stuff with a removable coupling, especially easy..
10ft stick, saw it in half, and you're almost done)


Do you have test equipment for tuning? Or are you looking for a
cookbook design that you can just build and know it will work as long as
the dimensions match the recipe?