Adding a Director to a ¼ wave 40M HF vertical antenna [复制链接]

http://www.ve1zacradio.antserve.org/40M%20director.htm
点击图片看大图

图片:b.jpg

图片:c.jpg

图片:d.jpg

我英文不好，我大概看了一下，他的意思如果把原来反射器做成他图中的结构后，原来长的部分（反射器）居然变成了引向器了。
图中的结构是反射器也接入到馈电点后，变成引向器，而原来的振子阻抗下降，而且下降很严重，基本为原来的25%，所以他在振子加了一个1：4阻抗变换。
引向器长度比振子长，长度这里没有理论基础，就给出一个参考，但一定比振子长！
这个引向器的形状一个大的箭头。
点击图片看大图。

图片:1.jpg

图片:2.jpg

图片:3.jpg

图片:4.jpg

图片:5.jpg

发夹能提高阻抗不？


算是比较详细的介绍了
Soooooo… a quick revisit to my old 20M rotating parasitic array was in order. Turns out there is mention of this sort of thing in John Devoldere’s new book as well ( Low Band DXing).  A quick model session.. and voila ! We have a simple ( VERY simple) director for this antenna, and about 3 dB of gain !

Here it is:  a simple wire that is attached at the base and held up by a fishing line halyard to the top of the mast, and another piece of fish line to hold the apex out from the base. This is a director, so it points in the direction you want to steer… like a big arrow!

Since the feedpoint impedance will drop precipitously when the coupling occurs properly, it is easy to adjust this thing by putting an impedance meter at the feedpoint and pulling the bottom leg around until you get a nice low reading. Worked like a charm. My model dimensions were just about right on.  Even better, the new feedpoint impedance was about 25% of the original. Why is that a good thing ? Makes matching easy, as I will explain  further on.

图片:a.jpg

阻抗部分的说明
Of course the feedpoint impedance is going to drop with a parasitic element. My model showed it to be about 25% or so, and that’s what it turned out to be. Well, if that’s the case, then a 4:1 UNUN transformer should match the thing handily to coax. Turns out I already had a 1:1 UNUN out there to isolate the coax feed line, so it turned out to be easy to add a simple switch at the base to allow me to switch the transformer from 1:1 to 4:1   This isn’t a very sophisticated UNUN, but it works fine for this job. In my case, I had a nice coax connector under the weather shield, and it was easy to insert this thing in series with the coax. I just reach under and flick that switch to change the impedance

内容来自Android手机客户端

      

天文看不懂。