Subj : Looking into HAMing...
To   : Frank
From : Angus McLeod
Date : Sat Aug 20 2005 09:28 am

  Re: Looking into HAMing...
  By: Frank to Deuce on Sat Aug 20 2005 01:40:00

 >     On the type I have built (1/2" copper pipe) the biggest problem is makin
 >   a strong/weather proof connection across the J. This may be an advantage t
 >   building one like Angus mentioned.

I use thin copper brake-pipe.  Or thick solid copper wire, like old coax 
inner.  I find a strip of wood that is a good fit inside my PVC pipe.  Cut 
a couple curved sections out of the two edges to nake a connection point:

	+---+
	|. .|
	|. .|
	|. .|
	|. .|
	|. .|
	 ) (
	|. .|
	|. .|
	+---+

I drill some holed near the edge and 'lace' the wire on to the two edges 
of the strip.  (If I had one to build now, I'd route a slot/groove in the 
edge and use an adhesive like epoxy to attach the wire.)  Run the wire 
down one side, across the bottom and partway up the other side, to make 
the J.  Clean and tin the bits of copper that run past the curved 
cut-outs.

Get your PVC tube and two end-caps.  Drill and attach a small eye-bolt in 
one and your SO-239 (or whatever connector) to the other.  Glue the 
eye-bolt end-cap to one end of the PVC.  Run a short section of coax from 
the inside of the SO-239 to the two tinned points, and tack-solder into 
place at the computed dimention, and mark on the wood alongside this 
point.

Slip the strip into the PVC, push-fit the SO-239 end, hoist up by the 
eye-bolt and measure the SWR.  Lower, remove end-cap and partially slide 
elements out, write SWR next to the mark made previously.  Desolder, move 
as apropriate, tack-join feed, mark again, reassemble, hoist and recheck 
SWR.  If you do this a few times you will have a series of marks on the 
wood strip labelled with the SWR at the frequency of interest (or the 
frequency at which the best SWR is given for this position of the feed).  

When you have found the spot that suits you, giving the best SWR at the 
band of interest, remove the bottom cap one more time, beef up the 
tack-join, and reattach the bottom cap with PVC adhesive.  

	http://www.anjo.com/misc/j-pole.jpg

This is one that I built about 15 years ago, and apart from a little 
discoloration is still going strong.  A lick of paint would improve 
appearances, if I thought that mattered...

Note the eye-bolt in the top cap.  This J-pole is intended to be hung from 
a line thrown over a tree branch or similar.  The doubled, back-to-back 
end caps in the base add a measure of rain-proofing for the So-239.  If 
the antenna looks a little tall, it's because this antenna is a 
two-element colinear J-pole, but the same construction works just as well 
on a single-element J.  If you want, you can replace the lowest end-cap 
with something that has a thread on it.  That would allow you to screw it 
on to the top of another length of PVC and raise it that way.

Whaddya think?


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