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Author Topic: SLOPING DIPOLE  (Read 2747 times)
N8CDN
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Posts: 20




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« on: March 30, 2002, 09:30:49 PM »

I am looking to install a dipole that will slope from approx: 30 ft down to approx: 10'. The over all lenght of the wire will be approx : 115' (if my math is correct!) the antenna will be fed with 450 ohm ladder line. My question is, will my radiation pattern be much different than a horizontal dipole? also would I be better off trimming the antenna to 102' to make it into a G5RV? Any advise would sure be appreciated.

Thanks and 73 de Terry
N8CDN
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KF4ZGZ
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Posts: 288


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« Reply #1 on: April 01, 2002, 06:38:55 AM »

I am going to answer this from experience, and without firing up EZNEC.
Being a sloper the antenna should show some gain in the direction of the lowest end. But.... with the high end only being 30 ft. this will compromise the gain on the lower bands. Most likely, there won't be any gain on 75/80m, and you should have some when you get to 15-10m. As a dipole, the pattern will depend greatly on the height above ground. the only place you will be a 1/4 wavelength from the ground will be the higher bands.
If you want the gain, try feeding the antenna at the high end and grounding the coax there. Either ground it to a tower, mast, or just drop a ground wire down to a couple on radials (60 ft. minimum) on the ground.
If you add a 90 turn coil of wire on 1 3/4 inch PVC pipe at the feedpoint, the antenna will tune 160m, but will be narrow banded. Also , for 160m you NEED three 60ft. radials...more would be better.

Actually I had better performance on the G5RV by adding wire...I know, it's now a zepp... but I went with 130 ft. and it worked great, except not 160m.
 
Good luck de Matt, kf4zgz

" The best antenna is the one you build yourself."
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WB2WIK
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Posts: 20633




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« Reply #2 on: April 01, 2002, 12:31:55 PM »

This is a far less than ideal installation, being so terribly low.  The average height of your "sloping" doublet, which is hardly sloping at all, is only 20 feet above ground.  Such close coupling to earth will tend to eliminate calculable resonances, so whether it's 102 feet or 115 feet or any other length won't matter much.

I'd feed it with ladder line all the way to the tuner to minimize line loss and just use it!  Theoretically, a 115' doublet will be resonant at about 4.1 MHz; however in your case, it will not be, because it's far too low to achieve such resonance.  It will be reactive pretty much everywhere.  That won't prevent you from making contacts with it!

WB2WIK/6
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