Jason Winningham wrote:
On Jul 1, 2007, at 4:23 PM, Ray Wells wrote:
Given that a J-pole is only a dipole with an alternative feed method
(i.e. at the end rather than the centre), I have to wonder where
this gain comes from.
beats me, but when we fly 'em on the balloons, the J-pole has a
better range. Could be that the lack of a balun isn't so bad with a
J-pole than with a dipole. Could be some other construction issue, too.
-Jason
kg4wsv
Was it a very old (about 35 years ago) QST article that headlined "My
Dipole Has A Gain Of 79dB"?
The crux of the article was that you need to know what you're comparing
with. In the magazine article the comparison was with a dummy load!!
When you run them in a balloon, do you hang the J-pole down from the
balloon?
The reason I ask is that a dipole has maximum radiation at right angle
to the element. An end-fed dipole is no different, providing the pattern
isn't being disturbed by "something". The J-pole, being an end-fed
dipole "should" be the same.
Here's the "but". If the feed section of a J-pole radiates (and it often
does), it radiates out of phase with the dipole element, causing the
radiation pattern to move away from being at right angles to the
element. With an inverted J-pole, i.e. one hanging down from the ballon,
the antenna pattern would have downward tilt, a desirable characteristic
given the height a balloon can achieve.
This could be a case of having the antenna pattern where you want it
rather than the absolute gain of the antenna, a case where your
particular antenna does indeed work better than some others.
Ray vk2tv
_______________________________________________
Xastir mailing list
Xastir@xastir.org
http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
