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Feed-Line Mismatch Mechanical Analogy

June 20th Fact-of-the-Day

If a mechanical wave was induced into one end of an infinite length rope, the wave would propagate down the rope to infinity and would never return. However, imagine what would happen if the far-end of a finite-length rope, for example a 15-meter rope, was attached to a solid object, such as a large tree trunk, and a mechanical wave was induced into the other end by whipping it up and down sinusoidally. Mechanical waves would propagate down the rope just as in the infinite-length case until they reached the tree trunk. If the tree trunk had the same mechanical impedance as the rope, it would move up and down with the rope and no energy would be reflected. However, a large tree trunk is much more difficult to move than rope and therefore has a different mechanical-impedance. The impedance mismatch would cause waves propagating down the rope to reflect back toward the sending end, just as electrical waves reflect back from a transmission-line impedance mismatch. ©2005 Martek International All rights reserved.

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