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"Richard Clark" wrote in message ... On Tue, 28 Sep 2004 13:52:05 GMT, "John Smith" wrote: Suppose I construct the antenna as shown except put a Tee at the bottom for convenience. What will be the impedance at that point? After all, that would now be the feed point, yes? No. The feed point is at the inner conductor connection to the outer conductor. The bend in the line (where you would put the tee) is merely a bend in the line. You could choose any point in the line, would that qualify it as a feed point? No. Your eye is merely drawn to it through the magic of an illustration's symmetry. As a practical matter, yes you could insert a tee there (provided you open one leg, you see? even here we have to maintain the continuity out to the true feed point). I think you misunderstand, but that is most likely because I have a hard time conveying what's in my mind. Especially in print and expecially at my age. I didn't used to have that problem... I take a half-wave (at 1.0 velocity factor) length of RG58 with a BNC connector on one end and make a hairpin loop. This is the left side of the folded dipole. The BNC connector is at the bottom center. I take another half-wave piece of RG58 with a BNC connector connected to the shield only, and make a hairpin loop for the right side of the folded dipole. Now I install a T at the bottom between the left and right sides. As for the upper element, I attach the center wire of the left half to the shield of the right half. I repeat, the center conductor of the coax on the right side is not used. Now I have an antenna completely constructed with a feedpoint at the bottom center via the T. What is the impedance at the T? I must add that my analysis on the Z transformation may be at fault. Again, my focus is in larger antennas where these kind of machinations would be prohibitive. Others should have chimed in by now, but they seem transfixed with my postings on politics or bored altogether. It seems to me that you already have the text description before you. Certainly in a 800+ page tome Kraus isn't mute on the subject? Almost mute, yes. The only discussion for this particular arrangement is beneath the figure where it says "(a) A folded dipole has zero potential at the midpoint of the lower dipole half at all frequencies. Thus, this point is ideal to attache a coaxial cable." On the other hand, you have the instrumentation and the scale of construction is not so demanding that you couldn't resolve this yourself at the bench in an evening. We have too many dream weavers here already and I have pleaded with them to perform simple tests that apparently befuddle them. Imagine me posing the task of taking several SWR measurements being responded to with 100 posting threads of confusion as to how! I recently got some of the instruments I now have. Owning them, however, does not mean I know what I'm doing with them. This is my first foray into UHF and the instruments and techniques are new to me. Yes, I can handle complex arithmetic, but that doesn't mean I know how to set up a test properly at 440 MHz. Resolve this in an evening? I first have to learn how to make the measurements with some accuracy and repeatability before I can get meaningful results. At this frequency, I've learned, even getting a true short circuit takes care. Also, I have nobody to work with me as I try all this new stuff. This group is the only resource I have with people who are knowledgeable enough to answer such questions. I'm doing the best I can. 73, John |