Regarding your question about Tom's reply, a ground screen is not
"seen" by a yagi. However, the height of the yagi is an important factor
for the TO angle because of the "mirrow" image formed under the ground.
I would not have used the word "null" but it is basically correct.
Now that we have the TO angle established, another factor comes into
being, called the "fresnel ( hope I spelled that right ) zone". This is
( oversimplification ) an area many hundreds of feet away where the
"mirror" and actual antenna match up. If you got the angle low enough,
it could in fact be miles away. Ever wonder why that antenna seems to
better in some directions? Take a look and see what's out there.
This really becomes an important if you have a ridge or such within a
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