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#11
February 12th 10, 01:39 AM
posted to rec.radio.amateur.antenna
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Transmission line stuff 5
K7ITM wrote:
On Feb 11, 8:02 am, phaedrus wrote: I seem to recall that ladder/open-wire feeders are relatively high impedance ~500 ohms. Is it possible to construct 50 ohm open wire feeder and if so, what would the spacing be? Thanks! Oh, and to more directly answer your question, the formula generally given for accurate description of the impedance of two parallel, round conductors of the same diameter, in air, is: Zo = 120 * invcosh(D/d) where D/d is the center-center distance and d is the conductor diameter. So... D/d for 50 ohms = cosh(50/120) = 1.088 For 1" diameter wires, you'd have to space them 0.088 inches apart, which is tough to maintain unless you embed them in a solid dielectric. or you go away from round wires... |
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