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Art, KB9MZ wrote:
"I can up my efficiency to 50 per cent by hanging a wire down from the dipole ends which I am not comfortable about---." Why would Art be uncomfortable about improving efficiency by hanging a wire down? Maybe he does not believe his model is correct. Maybe he doesn`t want some directivity change that comes with hanging a wire down. Maybe there is some physical problem with hanging a wire down. The problem with a loading coil is increased loss. Capacitance is usually low loss. As Yuri, K3BU has noted, there is much to be learned from reading ON4UN`s Chapter 9 about antenna loading even though everything regarding vertical antennas doesn`t translate readily to horizontal antennas. ON4UN includes horizontally polarized antennas in "Low-Band DXing". It`s easy to read, well illustrated, and full of good references. It helps if you want to design your own antenna because it tells why as well as how. Best regards, Richard Harrison, KB5WZI |
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Art, KB9MZ wrote:
"Are you suggesting using a capacitive coupling instead of an inductor?" The dipole is about the simplest standing wave antenna. Its system must be resonant to allow full current in the antenna. The best arrangement for a dipole is a centerfed balanced pair of wires in a straight line that is self-resonant but this is only possible at discrete frequencies. If an antenna is too short to be resonant, it may be resonated by adding to its inductance or its capacitance, or both, if the antenna can`t be lengthened. My remark was only a reiteration of common knowledge. Coils are lossy and capacitors tend to be nearly lossless. Cecil has shown how an all-wave system with small losses can be made that doesn`t even require a tuner. He uses a variety of selected ladder line lengths to maximize antenna current. Another option is to use a balanced dipole with a balanced line connected with the transmitter through a tuner. Bill Orr, W6SAI has a suggestion for reducing the range of impedances the tuner must handle. It is to make the sum of the dipole length and the feedline length into preferred sums. These are 110, 133, 177, or 212 feet. He shows how to make the dipole, balanced line, and tuner in his book "Wire Antennas". He calls the dipole, line, and tuner: "A Universal H-F Antenna System", to cover 3.5 to 29.7 MHz with one antenna. Best regards, Richard Harrison, KB5WZI |
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