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"Tom Sedlack" wrote What kind of voltages and currents are present at the
ends of dipoles assuming 100W of RF and the antenna being close to resonant? ----------------------------------------------- A half-wave dipole is a resonant L & C tuned circuit. Its lumped equivalent is a series L and C circuit across the feedpoint. It has a Q value like any other resonant circuit. As is usual, Q = Inductive reactance of wire divided by resistance. In the case of a dipole the resistance is the radiation resistance at its centre, typically around 70 ohms. Inductance gets smaller as wire diameter increases. So a 2-meter dipole with 1" diameter tubes has a lower Q (about 4) than a 160-meter dipole made with 18 gauge wire. (about 12). Q controls bandwidth. A 40 meter dipole may have a Q around 9. If it is fed at its centre with 100 watts then the feeding voltage is 84 volts. So the voltage difference between the ends of the dipole is Q times 84 = 756 volts. Relative to ground, the voltage at one end of the dipole is half of this, equal to 378 volts. This would burn a nice little hole at the tip of your right forefinger if you touched it. Electrical burns take a long time to heal because the surrounding flesh is electrocuted. Do not confuse this with 'skin effect'. ---- Reg, G4FGQ |
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