A 50-ohm cable?
Early in my explorations of electricity, I came across a length of coaxial cable with the label "50 ohms" printed along its outer sheath. (Figure below) Now, coaxial cable is a two-conductor cable made...
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Circuits and the Speed of Light
Suppose we had a simple one-battery, one-lamp circuit controlled by a switch. When the switch is closed, the lamp immediately lights. When the switch is opened, the lamp immediately darkens: (Figure...
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Characteristic Impedance
Suppose, though, that we had a set of parallel wires of infinite length, with no lamp at the end. What would happen when we close the switch? Being that there is no longer a load at the end of the...
View ArticleFinite-Length Transmission Lines
A transmission line of infinite length is an interesting abstraction, but physically impossible. All transmission lines have some finite length, and as such do not behave precisely the same as an...
View Article"Long" and "Short" Transmission Lines
In DC and low-frequency AC circuits, the characteristic impedance of parallel wires is usually ignored. This includes the use of coaxial cables in instrument circuits, often employed to protect weak...
View ArticleStanding Waves and Resonance
Whenever there is a mismatch of impedance between transmission line and load, reflections will occur. If the incident signal is a continuous AC waveform, these reflections will mix with more of the...
View ArticleImpedance Transformation
Standing waves at the resonant frequency points of an open- or short-circuited transmission line produce unusual effects. When the signal frequency is such that exactly 1/2 wave or some multiple...
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Waveguides
A waveguide is a special form of transmission line consisting of a hollow, metal tube. The tube wall provides distributed inductance, while the empty space between the tube walls provide distributed...
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