The Smith chart, invented by Phillip H. Smith (1905-1987), is a graphical aid or nomogram designed for electrical and electronics engineers specializing in radio frequency (RF) engineering to assist in solving problems with transmission lines and matching circuits.
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The Smith chart, invented by Phillip H. Smith (1905-1987) http://en.wikipedia.org/wiki/Smith_chart#cite_note-0
http://en.wikipedia.org/wiki/Smith_chart#cite_note-1 is a graphical aid or nomogram designed for electrical and electronics engineers specializing in radio frequency (RF) engineering to assist in solving problems with transmission lines and matching circuits.
Transmission lines, and matching circuits have all to do about matching impedence (resistance).
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This is a Smith Chart.
The circles, all tangent to each other, represent different resistances. The one closest to the tangent represents an infinite resistance, and the one furthest out (largest circle) represents zero resistance. The curved lines represent reactances, from zero (the straight line) to shorter curved lines, the ones representing larger reactances.
The Smith Chart is used to do antenna calculations by drawing lines rather than using formulas.
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The Smith chart is plotted on the complex reflection coefficient plane in two dimensions and is scaled in normalised impedance (the most common), normalised admittance or both, using different colours to distinguish between them. These are often known as the Z, Y and YZ Smith charts respectively. Normalised scaling allows the Smith chart to be used for problems involving any characteristic or system impedance which is represented by the center point of the chart. The most commonly used normalization impedance is 50 ohms. Once an answer is obtained through the graphical constructions described below, it is straightforward to convert between normalised impedance (or normalised admittance) and the corresponding unnormalized value by multiplying by the characteristic impedance (admittance). Reflection coefficients can be read directly from the chart as they are unit-less parameters. Wikipedia.org https://en.wikipedia.org/wiki/Smith_chart
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The circles already present on the Smith chart include those for the resistive and reactive components of the normalized load impedance. One would normally use the intersection of these circles to identify the magnitude and angle of gamma, the voltage reflection coefficient.
By maintaining a gamma of constant magnitude about the origin, one can draw a third group of circles. Because standing wave ratio only depends on this magnitude, these circles define the standing wave ratio.
Thus, the correct answer is Standing-wave ratio circles.
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In the days of slide rules, the Smith chart was packed with lines, curves, grids and nomographs.
In the ARRL Extra class manual a Smith chart is introduced as an XY-coordinate graph where the top and bottom of the Y axis is bent to the right to touch the X axis at the infinite resistance point. These are the constant resistance circles. THESE ARE NOT the arcs the test is asking about.
The "arcs" are the lines that intersect the bent Y-axis lines, coming from the infinite resistance point out to the edge of the circle. These arcs represent points with constant reactance.
To interpret impedance on the Smith chart, it is necessary to understand constant resistance circles and constant reactance arcs.
A very comprehensive and in-depth depiction of Smith Charts can be found at Wikipedia
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The wavelength scales on a Smith chart are calibrated in fractions of transmission line electrical wavelength.
The outer ring of a Smith Chart defines fractional electrical wavelength of feedline starting at zero and ending at 0.5 (half the electrical wavelength). It also defines the direction toward the generator. This is a hint, indicating that this is a feedline length and not antenna length.
Smith Charts are useful to determine feedline line length required to match a load to a radio transmitter.
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