I built one of Kent Britain's "Cheap LEO Antennas" as a handheld antenna, and I have a question.
I built mine on a 3/4 inch ID PVC boom. works great!. Anyway, there are a good number of designs out there that use a folded dipole for the driven element, Kent's is of course "half" folded. However each of these folded elements I see, it is folded perpendicular to the plane of the antenna. (in otherwords, if the antenna lays flat on the floor, the element fold is vertical) I have a small 2 meter antenna that uses one and its perpendicular also. My question is, to simplify mounting to a small diameter insulated boom, could such an element be placed "laying down", so the element could be better supported by drilling 2 holes in the boom? In a normal folded element, balanced, I would assume the radiation center would be located at the center between the 2 parallel rods. The thoery that Kent uses for his states that the "j" portion of his, the J is the matching section, and the half wavelength rod, I would then assume to be the radiator.
I'm building this one to replace a "permanent" station antenna, which uses tee matches for the drivens. Kent's is easier to build, and would be easier to do if the element could be laid down on its side. Would like to get your thoughts on the thoery. I wouldnt think it would matter, as either way, its a dipole, and they all radiate 360 degrees around the element. Just trying to figure out why theyre all designed in the orientation that they are. Michael Heim ARS KD0AR
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On Sep 21, 2008, at 5:22 AM, Michael Heim wrote:
My question is, to simplify mounting to a small diameter insulated boom, could such an element be placed "laying down", so the element could be better supported by drilling 2 holes in the boom?
Michael - W7ZOI built one of the WA5VJB Yagi antennas for 2M using a driven element oriented just as you describe. He said it worked just fine.
I think you want the long part of the driven element to be in the same position in both antennas, but you may want to model it to verify this. The position is not too critical for 2M.
In Kent's antennas, the position of the driver from the reflector largely determines the impedance of the antenna, and the position of the first director from the driven element largely drives the SWR bandwidth. The gain sort of comes along from these positions for the three element beam and when there are more than one directors, these pretty much determine the gain.
They are nice antennas aren't they. I have built and used a half dozen for various bands and they all work great as built. I use them at the home station for terrestrial and satellite use, and in the rover. Now if Kent would only make some longer boom designs available. - Duffey -- KK6MC James Duffey Cedar Crest NM
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Michael Heim