[50mhz] Fw: Antenna gain? j-pole

[Ray Brown]

  For those of us debating about building and putting up a home-made
6m j-pole (like I did, but not quite like this)...


----- Original Message ----- 
From: "Dexter McIntyre" <dmcintyre@att.net>


> The J-pole is probably the most discussed and cussed VHF antenna ever
> conceived.  I've built my share most of which I was never pleased with. 
> One day while looking at some old ham publications, 50's vintage I
> believe, I saw a j-pole fed with a 4:1 coaxial balun. This probably was
> a Bill Orr article.  Anything wrote by Bill Orr I read.
> 
> Since I had tried every other possible method of connecting a feed line
> to a j-pole I figured I would give this a try.  First I built a 6 meter
> all copper j-pole and fed it directly with coax in all the know
> methods.  Every feed I tried showed lots of feed line radiation.  This
> was evident because the tuning would change just by moving the feed line
> or placing a hand on the line anywhere within a few feet below the
> antenna.  This feed line radiation is what makes the antenna such an
> unpredictable performer.
> 
> I then connected a coaxial 4:1 balun to the antenna.  After tuning the
> feed point a little a perfect match was obtained and there was
> absolutely no feed line radiation.  Since this type of balun leaves the
> shield of the coax ungrounded at the feed point I experimented with
> grounding it.  No change was measured by adding a ground from the coax
> shield to the center of the 1/4 wave horizontal support.  Out the top of
> a tower, rotating this antenna shows it to have a perfect
> omni-directional pattern.  I had never seen this before with a j-pole.
> 
> So my opinion of this antenna has changed.  Feed it properly, as a
> balanced fed antenna, and it will perform well.  I haven't tried it side
> mounted but I suspect it's performance would be equal to a side mounted
> dipole.  But if one wants a side mounted half wave antenna why not just
> use a dipole which would be at least 1/4 wave shorter than a j-pole.
> 
> A few pictures of the balanced fed 6 meter j-pole can be seen at:
> 
> http://www.w4dex.com/6mjpole.htm
> 
> Dexter, W4DEX
>