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Author Topic: Feeding Horizontal Loop  (Read 1002 times)
EI2HPB
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Posts: 39




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« on: December 28, 2012, 01:23:58 PM »

I'm sure this is answered on here hundreds of times so apologies in advance... I want to put up a 40m loop and due to the small size of my yard/garden it will have to be horizontal to fit the space... I know vertical is better for DX but I cant get the height to hang it that way... my question is, when the feed point and the legs are all the same height from the ground and the loop is horizontal does the same rule still apply regarding the feed point as when its vertical, ie fed from corner, side, apex etc to determine the polarization or does it matter as much when all the sides are equal height from the ground? many thanks.. EI2HPB
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K3VAT
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« Reply #1 on: December 28, 2012, 01:48:18 PM »

I'm sure this is answered on here hundreds of times so apologies in advance... I want to put up a 40m loop and due to the small size of my yard/garden it will have to be horizontal to fit the space... I know vertical is better for DX but I cant get the height to hang it that way... my question is, when the feed point and the legs are all the same height from the ground and the loop is horizontal does the same rule still apply regarding the feed point as when its vertical, ie fed from corner, side, apex etc to determine the polarization or does it matter as much when all the sides are equal height from the ground? many thanks.. EI2HPB

HNY, I didn't see how high up the four corners will be - that will determine alot on how the loop performs.  Generally, the horizontal loop will be horizontally polarized and as such does good to quite good if the lowest operating band is approaching 1/2 wave above average terrain.  Additionally, tell us if you can construct a 142' loop (approx 35' each side) - that will make it a full wave on 40 and will be quite beneficial.  Generally, you can position the feedpoint anywhere along the loop, but being more specific on the loop typology (and where the shack is located) will help to optimize.  

For additional notes, see the "Horizontal Fullwave Loop, Weird SWR Curve" by AK4SK (just updated).

GL 73, Rich, K3VAT

PS: feel free to use the search engine for this Forum  Grin
« Last Edit: December 28, 2012, 02:27:18 PM by K3VAT » Logged
WX7G
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Posts: 5985




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« Reply #2 on: December 28, 2012, 03:29:23 PM »

No matter where you feed a horizontal loop the radiation is horizontally polarized.

I would feed it where it is mechanically convenient.
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EI2HPB
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Posts: 39




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« Reply #3 on: December 28, 2012, 05:41:59 PM »

No matter where you feed a horizontal loop the radiation is horizontally polarized.

I would feed it where it is mechanically convenient.

Thank you that is exactly the answer I was looking for Smiley

Due again to mechanical restrictions the loop will be no more than about 28ft from the ground suspended from some poles at each corner of the garden, I plan to make it a full wave (142ft) on 40m... I'm sure the low height wont help but I'm gonna give it a whirl anyway... worse case it sucks and I take it back down... God loves a trier Grin
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WB6BYU
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« Reply #4 on: December 28, 2012, 07:40:38 PM »

While you're experimenting, you need one or more vertical wires (or at least wires with
a vertical component) to get vertical polarization.  If you have 4 posts around your
garden you could use them to support a short vertical loop.

For example, a loop with the top wire at 28' and the bottom wire at 10' would be
54' long for 40m, and would give low angle radiation if fed in the middle of one
of the vertical wires.  Feedpoint impedance is about 50 ohms.

[Typically such a loop is close to 50 ohms when it is twice as wide as it is tall, but
in this case it is shorter and longer because the ground losses raise the impedance.
If the resistance is too high, make it shorter and longer; if to low, make it taller
and shorter in length.]

If your posts form a square big enough for a horizontal 40m loop (say 36' on a side)
you can anchor the antenna from one post, run it towards an adjacent corner and
then bend it towards the next one around.  It will take up less than 2 sides of the
garden.  (It also may require a bit more wire than for the straight version.)  Maximum
radiation will be broadside to the two vertical ends.
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K3VAT
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« Reply #5 on: December 29, 2012, 06:20:44 AM »

No matter where you feed a horizontal loop the radiation is horizontally polarized.

I would feed it where it is mechanically convenient.

That's indeed correct, but only part of the equation.  As was pointed out by G3TXQ in the Topic "Tuning a horizontal quad ..." where he notes, "You can lower the SWR by adjusting the ladderline length as I suggested in my first posting - the ladderline is part of the antenna system! But if you use coax all the way from the loop, the size of loop is the only available adjustment."  So knowing a bit about loop typology, method of feed, and observed SWR, one may have an opportunity to optimize the system.  GL, K3VAT.
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N1CX
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Posts: 121




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« Reply #6 on: December 30, 2012, 06:06:36 AM »

If you can't get the height for a full vertical loop then make it a triangle. Get the center as high as you can then feed it with a balun at the 1/3 up point from one bottom corner. It will be one of the best antennas you would ever have.
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