Building a Beam Antenna

[K0LDS]

I see lots of great ideas for 2 meter beam antenna construction out on the Internet, and I'm going to experiment with some shortly…..A question comes to mind that I'm not finding in my antenna books: Does it matter (or what is the effect) of the director, reflector and other antenna elements either touching or not touching the antenna boom as they are inserted through the boom of the antenna? I would imagine that the antenna resonant frequency would be changed, but are there any other effects one would need to consider, between a boom that conducts RF energy (metal), and one that doesn't (i.e. wood)?Thanks for the help, I'm not having any luck finding anything on this in the antenna literature I have searched in the last month.Ted K0LDS, Pueblo, CO.

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[VA7DH]

Hi, you must have not been fortunate in finding the right antenna literature. Yes, there is a difference at to whether the boom is conductibe (aluminum round or square tube) or whether it is made of fibreglass, PVC, or wood. If the elements are floated off the conductive beam they will still be affected by the proximity of the beam and so the lengths will be slightlly different. Wood makes a nice beam to support elements but you need to treat it so it doesn't rot. PVC can be used but it tends to get a little droopy especially in the heat so you need to support the ends. I just found an interesting web site at –http://www.mydarc.de/dk7zb/PVC-Yagis/PVC-details.htmYou can see some PVC boom Yagis there and how he has supported them. I find that filling the inside with a wood dowel helps stiffen them some. One article I read mentioned that metal beams can have the elements fastened to them but beware of corrosion products that can cause noise where the elements are fastened. This can be a real problem where I live and am enveloped with a sea side atmosphere, has salt in the air and rain. By insulating the elements he claims that problem doesn't exist. Another way would be to TIG weld the elements to the boom. If you are using a non conductive boom then that problem would not exist.

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