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CDT,

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Well a simple answer is that there are two parts to Impedance. One part is the resistance that can be measured by your ohm meter. That is DC resistance. When you apply an ac signal to the device, then if there is some magnetic materials that would create magnetic fields an Inductive component along with the static electric fields (an Inductive component) then you get some components that impede the flow of electricity, hence impedance. The reason that is important is that if impedances are matched then the signal flows through the circuit without much loss (loss due to the dc resistance).? They call that impedance matching.? You can see some of those effects with waves on the water. If the waves hit a barrier then the waves are reflected back. If they don't hit a barrier they just keep going.?

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fIf you have a rope tied to wall and shake the rope, the wave goes to the wall and is reflected back. But if you have a thin rope tied to a much thicker rope that is then connected to the wall then when you shake the rope, when the wave hits the junction of the thin and the thick rope, some physics magic happens, some of the wave moves into the thick rope but some of the wave is reflected back to the thin rope (as though it kind of hit a wall) this is what is called an Impedance Missmatch.? The original wave will continue on the thick rope until it hits the wall on the thick rope and the wave will reflect back along the thick rope (Impedance mismatch between the thick rope and the wall).

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So what we see now is a wave traveling back along the thin rope (first reflection from the impedance mismatch between the thick and thin ropes) and we see the original wave starting to travel back from the wall along the thick rope.?

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When that reflected wave of the original signal on the thick rope that is traveling back from the wall hits the junction with the thin rope, some of that wave will move onto the thin rope and some of that wave will reflect back towards the wall (because of the Impedance mismatch between the two ropes).

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So what we see now (depending on the length of the thin rope compared to the thick rope) is a reflection of the original wave from the junction of the two ropes traveling back at you, and a smaller reflection of the original wave traveling back to you that bounced off the wall and crossed the rope junction, and a reflection of that from the rope junction traveling back towards the wall on the thick rope.

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The space between the two impedance matches will have reflections sloshing back and forth diminishing over time.??

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Lets say you gave the original signal one sine wave, (one up down back to center flip), and you listened to the rope, you would first see a small reflection back from the rope junction, then a larger (depending on all the impedance mismatches) from the signal that reflected back from the wall, then you would continue to see smaller and smaller signals coming from the ringing in the thick rope that escaped over the rope junction.

There is more technical detail with phase changes and such but that can get in the way of understanding the fundamental effects of Impedance mismatches.

So Impedance matches are important to limit reflections which is another way of saying resistance to your signal getting to the antenna or back from the antenna. The SWR? Standing Wave Ratio is a measure of the transmitted energy to the reflected energy and is a measure of how much of your signal makes it through to the antenna. So devices that have an impedance rating like 50 ohms are geared to connect to other 50 ohm devices and not reflect much energy. So readings should be more accurate because nothing is lost in the connection between devices.

Hope this narrative helps you understand some of those issues on a very coarse level. But good and important information esp. for low power operations like the ubitx and other QRP rigs.?

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? ?---John AC9UV