03-13-2012, 02:35 PM
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Join Date: Dec 2008
Location: Silicon Valley CA, Storm Lake IA
Originally Posted by hammer0630
Damn, I wish I could understand this graph. It looks like some one transmitting at the North Pole and the signal is being sent east against it's will.
That graph is not a radiation plot of a vertical antenna; looks like the plot of a Yagi beam to me.
First of all, let's understand that each color is the antenna radiating at a different height above ground.
30, 35, and 40 ft
Look at this radiation plot as if you were standing and looking at a Yagi beam antenna pointed twards the East, and you are South of that beam antenna. Those two larger lobes are the angles of radiation relative to the horizon. There are two main lobes, and these will both 'shoot' RF radiation twards the ionosphere at those same two different angles. The longer lobe is 15 degrees to the horizon and stronger, and the shorter lobe isn't quite as strong and is approximately 45 degrees to the horizon. The longer lobe is at a lower angle and throws the radiation potentially farther.
When you were a kid and threw small, flat stones across a pond - you had to throw them at a low angle at that pond if you wanted that rock to skip across the pond as many times as it could. Perhaps a poor analogy; but fair enough . . .
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Last edited by Robb; 03-13-2012 at 05:23 PM.