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Buck wrote:
Is this a single band or multiband antenna? If I recall correctly, you can use a different impedance feedline if it is a multiple of a half wave. At the half wave points, the impedance is the same as the beginning of the feed. i.e. at the antenna. You're right, neglecting losses, the antenna impedance is repeated every half wavelength. Neglecting losses, that 100 ohm antenna feedpoint impedance will be repeated at half- wavelength intervals for *any* feedline Z0, including 50 ohm coax. Cecil or others here will correct the length error if I am incorrect. But I learned about a year ago that the impedance can be corrected by the multi-fraction length feedline of a different impedance. Maybe this is the principal of Cecil's feedline matching system. The principal of the feedline matching system that I use is that every SWR circle crosses the purely low resistive point at a current maximum point. For dipoles that are 1/2WL on the lowest frequency of operation, the current maximum point is the ideal point at which to feed the antenna system. Adjust the length of the feedline until the current maximum point is at the transmitter and you will usually not need a tuner at all. -- 73, Cecil http://www.qsl.net/w5dxp |
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