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Author Topic: Loop As Top Loaded Vertical  (Read 1310 times)
K3ZL
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Posts: 124




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« on: March 04, 2011, 11:05:26 AM »

I am experimenting with a 80 meter full wave loop. It works well, but as an experiment I have fed it by connecting both conductors of the window line together connected to the Plus side of my 4:1 balun in my shack.  I connect the Negative side of the balun to my ground system.  It works pretty well also. Am thinking about putting a ground radial system under the loop which may be useful when using it as described as a vertical.  As a loop it would be an ungrounded antenna, but as a vertical I am wondering of this could be useful? The feed point of the loop is at the top of a fiberglass mast.  My question is, when making this radial system, should I tie it into my station ground system, or just lay out the radials under the loop?
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WB6BYU
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« Reply #1 on: March 04, 2011, 11:58:23 AM »

In that case you are using the feedline as a vertical radiator.  The input impedance will depend
on the length, but radials are a good idea.  Since the feedpoint in that case is at the bottom
of the feeder (in the shack it sounds like) that is where the radials should be connected.


The radiation from the resulting antenna is not entirely vertical, however.  There will be a
high impedance at the loop feedpoint when the loop is used as a top hat, and the current
distribution in the loop will be the same as if the loop were feed in a normal manner 90 degrees
around the perimeter.  (In this regard it is rather like using a half wave end-fed wire as a top
hat.)  The horizontally polarized radiation will be a significant part of the total.  The input
impedance at the feedpoint (in the shack) will be fairly low unless the ladder line is over
3/8 wave long so radials are important to keep losses low.

DX performance is somewhat better than the loop itself, but probably not as good as
using just the feedline alone without the loop, since the loop as a top loading structure
will add pickup of high angle signals that may interfere with receiving DX.
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W4VR
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« Reply #2 on: March 06, 2011, 08:32:28 AM »

I had a vertically mounted delta loop on 80 meters many years ago.  The base of the triangle was about 8 feet above ground.  I installed forty 60-foot radials centered under the horizontal section.  I would short out the loop and feed it on 160 meters with an L network at ground level where the coax came in...worked very well.  I don't remember having any connection between the radial center and the electric mains entrance ground and never had any problems.
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K3ZL
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Posts: 124




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« Reply #3 on: March 07, 2011, 08:30:00 AM »

I had a vertically mounted delta loop on 80 meters many years ago.  The base of the triangle was about 8 feet above ground.  I installed forty 60-foot radials centered under the horizontal section.  I would short out the loop and feed it on 160 meters with an L network at ground level where the coax came in...worked very well.  I don't remember having any connection between the radial center and the electric mains entrance ground and never had any problems.

That sounds right.  Since mine is horizontal I believe I will center my radials  below the feedpoint, as suggested by WB6BYU,  and lay them out on the ground underneath the entire plane of the loop.  Will take data on it before and after and let you know how it does. Tnx for the suggestions.
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WX7G
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Posts: 5920




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« Reply #4 on: March 09, 2011, 07:54:25 AM »

Remove the balun and feed it directly to the tuner.
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