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Author Topic: 450 Ohm Line, what balun to use  (Read 2037 times)
K8KAS
Member

Posts: 569




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« Reply #30 on: August 06, 2007, 10:19:33 AM »

Your 80 dipole can be feed with balanced line either 300 or 450, really won't matter to the shack. The balun can be a 4:1 or 6:1 but ground the center tap
of the balun to a good RF ground at the entrance. I use 30---50 foot radials for this RF shack ground ground. I have NO RF in the shack even running 1500 watts.
Your really lost on your 160 meter antenna, a 1/4 wave will with a good RF ground shows around 20 to 25 ohms feed point resistance, your can match this with  25 ohm/50 ohm
unbalanced balun or an auto-transformer matching device. This is a coil with the coax tapped up 3 to 5 turns from the bottem and then tap above to resonate to freq. The bottom of the coil goes to the ground system. A quarter wave is a CURRENT fed antenna and shows a low feed point impedance. keep the antenna less than 120 feet and it will match very EZ with the Auto Trans match.
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N0LOH
Member

Posts: 31




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« Reply #31 on: August 08, 2007, 10:54:56 AM »

I am so glad someone posted the link to DxEngineering. I just purchased a 1:1 balun for a 40-meter dipole fed with 450-ohm line and when I came upon this thread, I thought I had done wrong.

I'm an advanced class, too, but I can't remember everything from when I studied for my exam.

Thanks eHam.net for such a wonderful free service! My Elmer, K0SVZ has been a Silent Key for many years.

I'm thankful to everyone who contributes in a positive manner to this forum.

"If you can't say something nice about someone, don't say anything at all." - Thumper's father.
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KC8OJU
Member

Posts: 31




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« Reply #32 on: June 01, 2008, 09:27:50 AM »

I just finished off a 128 feet folded dipole, fed with 32 feet of homebrew ladder line, 300 ohm. I used a 4:1 FT240 toroid balun using 17 turns of bifilar wire. The 4:1 balun into a 3 feet RG8X into a loaner TS850 Kenwood.

 I got a 1:1 match across the expected frequency 3.6Mhz to 3.69Mhz. So a 300 ohm antenna and 300 ohm feed line with a 4:1 balun should be 75 ohms and a 1.5:1 match.

Now if you are really sharp you know where the 1.5:1 match got transposed to 1:1

73
N8ZU
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