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David wrote:
RF transmitter output has impedance of 50 ohms and is connected to dipole with a feedpoint impedance of 50 ohms via feeder with characteristic impedance of 50 ohms. System is perfectly matched. I expect SWR meter to show perfect match of 1:1. Dipole has a standing wave on it. Ends of dipole are at high voltage. Dipole is centre-fed with centre being high current point. Standing wave means that a reflected wave exists. Wave is reflected from open ends of dipole. What happens to the reflected wave? How does it vanish at centre of dipole? Why does reflected wave not go along feeder into transmitter output? There cannot be a reflected wave on feeder because SWR is 1:1. If the reflection is exactly in phase with the next wave arriving through the feed line, then it just raises the impedance the line sees. In other words, the reflection acts as a large part of the feed energy for the next cycle. It doesn't bounce into and out of the feed line, it bounces back and forth from end to end of the dipole. Actually there are two reflected waves going in opposite directions, end to end, simultaneously. |
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