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

November 14th 03, 05:28 PM

oSaddam (Yuri Blanarovich) wrote in message

Mike,
to put in perspective, and I tried to point out in the course of threading this
thread, the significance is this:

1. Impact on effciency - efficiency is roughly proportional to the area under
the current curve over the radiator. When the current drop across the coil is
significant, that "eats" the portion of the curve and the curve above the coil
is much smaller (cosine or triangle shape), less efficiency

Sure, it's called varying stinger heights, or varying capacitance. The
less stinger you have, the less current will be pulled through the
coil. Thats the way I see it anyway. If you noticed a taper across a
coil, what would you do about it? How are you going to improve the
antenna, if #1 , the coil is already as high as you can place it, and
#2, the stinger is as long as you can make it.

2. Understanding the effect allows to better optimize the antenna performance,
be it through modeling or experimenting and measuring.

How? I don't see how we can improve over what we are using. We are
already using the optimum coil placement if we want that. Vertload can
tell you that very quickly.

That's why top hats look
so good. We are not talking just fraction of dB, on low bands that shows as 10s of dBs on signal.

Huh? Top hats work well, because of a current taper across the coil?
Top hats don't model properly because of a current taper across a
coil? I'm confused...

3. Proper modeling in software will allow better design and optimization. See
case of linear loaded 80m KLM beam vs. modified with loading coils, big
difference in pattern and gain and performance.

Where would I see this? Normally, I would expect the lumped coil
version to be the most efficient if quality coils are used...

4. If the modeling software can not capture the effect, than your designs of
multielement loaded antennas are off.

Thats a big if though...I've already shown that the likely error from
this "taper" would most likely be so small to be unnoticed. So far, no
one has shown it to be otherwise.

This exercise already opened my eyes wider and after I test the designs, I will
hopefully come up with some better mobile antennas.

Yuri

Thats the bottom line. But I still feel I'm already building mine as
well as they can be. MK