| Author |
Message |
    
Apocolypse400
| | Posted on Thursday, October 10, 2002 - 10:33 pm: | 
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Whats the diffrence between a vertical dipole and a fiberglass 102" whip with a 102" piece of wire attached to the grounded side. Used as base antenna?
Steve |
Ryan
| | Posted on Monday, December 02, 2002 - 7:54 pm: |
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not a thing
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Apocolypse400
| | Posted on Tuesday, December 03, 2002 - 12:23 am: |
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Well I did figure that one out on my own, but thanks anyway. I found a old arrl antenna book and am slowly workin my way through it. I am up to Simple quads and phasing. Whew...... The physics is kinda rough though. I have a hard time understanding the effects of Reflectors and Directors, and how many of them work in conjunction, but I am getting it, I think.
Steve |
Tech833
| | Posted on Tuesday, December 03, 2002 - 11:58 am: |
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Think of directors as lenses like on a camera. The effect a director has is very similar to focusing a lens in that you are 'focusing' the magnetic field (through phase vectors) of the driven element.
That makes it easier for most people to understand. |
Apocolypse400
| | Posted on Tuesday, December 03, 2002 - 10:30 pm: |
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With a Yagi I see a 2D plane, but when the magnetic field is emitted you have a 3D lobe??? The directors would only effect the horizontal lobe and not the vertical component of the field?? So you have a vertical field that is uneffected by the director and is emitted 360 degrees around the antenna???? If I am right up to this point, you would see reflected energy in the horizontal plane caused by the omni-directional field? I just dont see how a horizontal reflector and director keeps the polarization constant.
My head hurts. |
Tech833
| | Posted on Wednesday, December 04, 2002 - 11:42 am: |
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I'll try to simplify this, I hope I succeed.
Don't think of it as a vertical field and a horizontal field, that's where you are complicating this. You need to understand that the electrical field and magnetic field are opposite poles of one another. Let me explain:
If you could magically 'see' a radio signal coming at you, it would look like a large grid, like a tic-tac-toe board. If the antenna was vertically polarized, the vertical lines would be the electrical field and the horizontal lines would be the magnetic field.
Now assume the magnetic field is radiating away from a vertical antenna element. If you were looking 'down' on it (so the antenna element was a dot), the magnetic field would form the 'ripples in the water' effect around that radiating element. The vertical field would look like straight lines flying away from the element like a spider web in all directions.
Got it so far? O.K., now if you add a director in that field in phase with the driven element (the pebble in the water) then which field would be the most affected? The ripples, right? O.K., now remembering that the electrical and magnetic fields are in proper phase in a resonant antenna element, the director 'skews' the magnetic field, and naturally, the electrical field changes with it.
Did that help or make your head hurt worse? |
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