Cecil Moore wrote:
Mark Keith wrote:
Why the 3/4 wave example?
In order to illustrate higher current at the top of the coil than
at the bottom, of course.
You should be able to find a configuration that provides max current
at the top of the coil, if what you claim is true.
I just did in the 3/4WL example. One cannot get higher current at
the top of the coil in a 1/4WL electrically long antenna. For a
1/4WL antenna, the maximum current is at the feedpoint and tapers
down to the tip.
uh huh.....
I want to see max current at the top of the coil in the SHORT
loaded 8ft mobile whip for 80m.
Well, good luck on that one. I think it's impossible. Blood out
of a turnip comes to mind. If you think I ever said or implied
that I could do that, you are as mistaken as you can possibly be.
What has all this been about? Bugcatchers and other short loaded mobile
antennas. All shorter than 1/4 wave.
Good grief....I rest my case.
My theory? I still think the current across the coil is *fairly*
constant.
I'm *still* of the opinion that the *apparent* radical taper across the
coil is more due to the presence of the capacitance above the coil. I
think Roy described this in more accurate terms, but I have to reread
the thread.
I'm *still* of the opinion that if you could measure the current INSIDE
the windings of the coil, a couple or three turns in from each end, you
would not see near the difference you all do. I do think it's quite
normal to have a slight taper, as you would with any other radiator that
is shorter than 1/4 wave. So what? But these are just my gut instincts
using my built in BS filter. I'm absolutely certain than any error in
modeling a short mobile antenna using lumped coils is not worth worrying
about. This was the main gist of the argument by Yuri. It was the bottom
line. He claimed we were modeling in fairly gross error due to this new
found revelation of coil current taper. He promised a new revelation in
coil positioning that would turn the mobile antenna world on it's head.
Or at least the hype seemed to imply this. But I'm afraid many beat him
to it years ago. As far as phasing coils, yep, you might have an issue
there. But it appears you may have been enlightened to a workaround even
in that case. Isn't life grand? MK
--
http://web.wt.net/~nm5k