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Tom Bruhns wrote:
If you measure the voltage drop along the wire, it's essentially zero, so along the wire the voltage between the end points of the dipole is essentially the same as the voltage across the feedpoint. Brain fart? The feedpoint impedance is the ratio of voltage to current. The feedpoint impedance of a halfwave centerfed is low, around 70 ohms. The feedpoint impedance of a halfwave endfed is high, thousands of ohms. The voltage at the middle of a dipole is low and the current is high. The same holds true for a 1/4WL monopole feedpoint fed against ground. The voltage at the ends of a 1/2WL monopole is high and the current is low. The same is true for the open end of a 1/4WL monopole. The sum of the forward wave and reflected wave causes standing waves on an antenna like the above. The voltages, currents, and impedances vary somewhat akin to an SWR circle on a Smith Chart. -- 73, Cecil, W5DXP |
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