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J-Pole coax center to short or long element?

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conve36

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May 5, 2008
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Menifee/Lake Elsinore, Ca
I have seen different designs for the j-pole and cant understand why they are all basically the same EXCEPT some designs specify to attach the center of the coax to the short stub and some say to attach it to the longer part of the antenna?? Comments?
 

hertzian

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May 28, 2009
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For most people, attaching the center conductor to the "long" side is the way to go. The elevation angle is lower than if you attach it to the short side. Matching is typically the same either way, so the issue is elevation angle.

Yet, there might be cases where you actually want a higher elevation angle - if you are in a canyon, have a mountain in your backyard etc. In this case, having the main lobe higher to catch knife-edge refraction off the top might be desired. In some cases, I've actually pointed yagis upwards to get this on VHF.

But typically, most need the lower angle, so the center conductor to the long side is the way to go.

You may also want to investigate choking near the feedpoint with ferrites to help ensure that you are indeed getting the lowest angle possible by not having the common-mode of the coax becoming part of the antenna.
 
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