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Author Topic: 80m verticle Delta Loop help needed  (Read 526 times)
EI2GLB
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Posts: 591




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« on: August 02, 2008, 12:48:45 PM »

Hi all

i hope to install a 80m delta to try work some dx in the comming winter season.

what im not to sure of is the feed arangement i know i feed it at one on the bottom corners

but do i just connect the center of the coax to the loop and earth the braid

or do i break the loop and feed the center to one side and the braid to another through a balun.

and is 1005/freq (mhz) a good formula to work with.


thanks

Trevor
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KB3XE
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Posts: 22




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« Reply #1 on: August 02, 2008, 01:58:25 PM »

I have a loop just like you want to build. You put an insulator at one corner and attach the braid to one side and attach the center conductor to the other side.

I used the same formula and had to do a bit of trimming to get the SWR down where I wanted.

I feed mine with a quarter wave section of RG 11 (75 ohm) to RG8. With this feed arrangement I was able to get a 1.1:1 SWR.

You could also feed the loop with open wire feedline directy to a tuner. I've done that also with a "home brew link coupled transmatch"...works great, but getting open wire feeders into the shack sometimes presents a problem.

If you just feed the loop with RG8 you probably will not be able to get the SWR down to 1.1:1, but even when I done that the auto tuner in my IC 761 was able to handle the slight mismatch.

Loops are a great antenna. I also have one up for 160, but it's a "cloud burner" It's a square about 50 feet above the ground.

Let me know how you make out.
73
Jerry  KB3XE
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K4SAV
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Posts: 1851




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« Reply #2 on: August 02, 2008, 02:11:53 PM »

If all the sides of the delta are of equal length, then feeding it about 25% from the bottom on one of the sides will give better gain and a more omni-directional pattern.  

Yes, you break the loop and insert the balun.  It should be a good match for a 4 to 1 balun.  

The feedpoint impedance and resonant frequency varies a little with the shape of the loop and height and exactly where you feed it, but if all the sides are equal, bare wire is used, and the bottom wire is close to the ground (maybe 10 ft) then 1028/f should be closer.

Jerry, K4SAV
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