RadioBanter - View Single Post

May 10th 06, 03:03 PM posted to rec.radio.amateur.antenna

wrote:
I once made a J-pole from 300-ohm twinlead and tweaked it until it worked
OK while hanging from the ceiling, but when I moved it over next to a
wood-framed picture window (hung it from the window casing), the SWR went
to pot. Did I do something wrong?

What kind of metal was behind the window frame?

The house was old enuf that I'm sure it was made of wood, and
since it was a PICTURE window, there were no sash weights, either.

So the question remains: are J-poles sensitive to nearby materials?

My limited experience with three J-Poles indicates that they are very
sensitive to nearby materials. I tried tuning in my shop which is
fairly cluttered and in the basement of a stucco finished townhouse. I
used thin rope to hang the J-Poles from an overhead floor joist.
Changing the location by only several inches changed the SWR. I found
a spot about four feet from the nearest object which gave the lowest
SWR. A ladder line J-pole was still very difficult to tune and it
changed significantly when it was moved to the attic. A copper J-Pole
was easier to tune but it also changed when it was moved to the attic.
The Arrow end fed was "store bought" so I didn't make any adjustments
in the basement. It had a reasonable SWR in the basement and it didn't
change when it was moved to the attic.

I did some more tuning of the copper J-Pole on my deck. SWR changed
with location, even though the deck is fairly open. The best SWR was
with the J-Pole in a 5 gallon pickle crock sitting near the center of
the deck.

jimbo