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Say you have a 1 kHz signal source with an impedance of 50 ohms and then connect a 100 ohm resistor between the terminals. Is the power that is reflected calculated in the same way as transmission lines (i.e reflection coefficient)?

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I know that in the case of an open circuit that all the power is reflected (even for low frequency circuits) which can be measured by a directional coupler.

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  • \$\begingroup\$ Yes, all the equations hold right down to DC, if you want to use them, and interpret them correctly. \$\endgroup\$
    – Neil_UK
    Commented Aug 9, 2022 at 16:16

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In short: yes. Your resistor actually has an impedance of 100 Ω. (For 1 kHz, that's not only theoretically, but also practically true. For 10 GHz, the parasitics/geometry of the resistor means it's not actually a 100Ω termination, but that's a different story.)

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Yes, it applies. It's just not used because it's more complicated than just using lumped-constant analysis.

Note that you can't assume that you don't have to pay attention at 1kHz: a 1kHz signal in free space has a wavelength of 300km or so, and that distance only goes down when you send it out on a real transmission line. You'll start seeing transmission line effects from one edge of a big city to another at 1kHz, and you'll definitely see them from city to city.

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