RadioBanter - View Single Post - Current in antenna loading coils controversy

October 31st 03, 02:50 AM

oSaddam (Yuri Blanarovich) wrote in message ...

I could buy that to an extent I guess. But say if you had a top loaded
vertical, with linear current distribution, the current across the
coil should be appx equal no matter where the coil is placed. But if
no top loading, maybe so.. MK

Top loaded vertical does not have LINEAR current distribution, that is another
simplification, fallacy. Current in the radiator has cosine distribution.

It's still fairly constant. But the degree would depend on the height
of the vertical vs the length of the top hat wires. If the hat is too
small, I doubt you would see as steady a distribution up the radiator.

At
the base, there is not much difference, just like in cosine of the angle
corresponding to the electrical length of radiator at that point.

I'm not sure what you mean by this. Do you mean the current across the
coil would be more steady than if the coil were higher? Does this
include using the top loading wires?

Again, this subject of current distribution is important in optimizing the
antenna design by fine tuning the position of the loading coil in the antenna,
combination with top loading etc. Morew current flowing in the radiating part
of the antenna - the stronger the field and louder signal.

Sure. But this is old news. I beat Reg's vertload program to death
finding the best overall coil height for my mobile antenna. Basically
I ended up putting it as high as I could. Which ended up a center load
at 5 ft up, with a 10 ft whip. Or 8 ft up on a 13 ft whip when parked,
and using the "Super" mode...

The "linear" current distribution mentioned in ARRL Compendium and Antenna Book
is the simplification propagated from Belrose's 1955 QST article. It is close,
but not exact and introduces confusion as it is demonstrated by the flat earth
society.

Dunno, I've never read it. Maybe calling the distribution as "linear"
is the wrong term, but the current is still fairly steady along the
radiator in the case of the vertical with the large top hat. I'm
looking at a model of one now. The current distribution is almost like
a twin tower standing next to the vertical. There is a slight decrease
from bottom to top, but it's very small. It's still my view that the
difference in current at each end of the coil used in such a case is
fairly small. No matter where the coil was mounted.
I've never said they would be exactly the same. Seems to me I started
off by saying they could vary a bit depending on the antenna. So if
you are saying they would be close, but not exact, you seem to be
saying the same thing I said to begin with, which seems to be the same
thing Cecil is saying. ??? Crap, I'm becoming confused.... I'm not
good at playing these type games. That's why I didn't even bother
reading the "current war" over on e-ham. *Sounds* like a 598 thread
nit pick contest just judging from what I've heard... It's not "that"
important to me, being I don't see what it would do for me, even if I
found there to be a fairly large difference from each end. If you have
pertinent info which shows the current is not even close to being
constant across the coil, please enlighten us. "I guess you are
attempting to" But at this point, I think everyone is starting to
chase their tales and bark at the moon.
I'm not really seeing the point, being the art of improving current
distribution in short verticals using coil placement is old news. MK