# Month: January 2021

# Smith chart – Wikipedia

The **Smith chart**, invented by Phillip H. Smith (1905–1987), and T. Mizuhashi,^{[3]} is a graphical calculator 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.^{[4]}^{[5]} The Smith chart can be used to simultaneously display multiple parameters including impedances, admittances, reflection coefficients, {\displaystyle S_{nn}\,} scattering parameters, noise figure circles, constant gain contours and regions for unconditional stability, including mechanical vibrations analysis.The Smith chart is most frequently used at or within the unity radius region. However, the remainder is still mathematically relevant, being used, for example, in oscillator design and stability analysis. While the use of paper Smith charts for solving the complex mathematics involved in matching problems has been largely replaced by software based methods, the Smith chart is still a very useful method of showing how RF parameters behave at one or more frequencies, an alternative to using tabular information. Thus most RF circuit analysis software includes a Smith chart option for the display of results and all but the simplest impedance measuring instruments can plot measured results on a Smith chart display.^{}

Source: *Smith chart – Wikipedia*

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# Installation · PlatformIO

Source: *Installation · PlatformIO*

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# Standing wave ratio

In radio engineering and telecommunications, **standing wave ratio** (**SWR**) is a measure of impedance matching of loads to the characteristic impedance of a transmission line or waveguide. Impedance mismatches result in standing waves along the transmission line, and SWR is defined as the ratio of the partial standing wave‘s amplitude at an antinode (maximum) to the amplitude at a node(minimum) along the line.

The SWR is usually thought of in terms of the maximum and minimum AC voltages along the transmission line, thus called the **voltage standing wave ratio** or **VSWR** (sometimes pronounced “vizwar”). For example, the VSWR value 1.2:1 means that an AC voltage, due to standing waves along the transmission line, will have a peak value 1.2 times that of the minimum AC voltage along that line, if the line is at least one half wavelength long. The SWR can be also defined as the ratio of the maximum amplitude to minimum amplitude of the transmission line’s currents, electric field strength, or the magnetic field strength. Neglecting transmission line loss, these ratios are identical.

The **power standing wave ratio** (**PSWR**) is defined as the square of the VSWR, however, this deprecated terminology has no physical relation to actual powers involved in transmission.

SWR is usually measured using a dedicated instrument called an SWR meter. Since SWR is a measure of the load impedance relative to the characteristic impedance of the transmission line in use (which together determine the reflection coefficient as described below), a given SWR meter can interpret the impedance it sees in terms of SWR only if it has been designed for that particular characteristic impedance. In practice most transmission lines used in these applications are coaxial cables with an impedance of either 50 or 75 ohms, so most SWR meters correspond to one of these.

Checking the SWR is a standard procedure in a radio station. Although the same information could be obtained by measuring the load’s impedance with an impedance analyzer (or “impedance bridge”), the SWR meter is simpler and more robust for this purpose. By measuring the magnitude of the impedance mismatch at the transmitter output it reveals problems due to either the antenna or the transmission line.

https://en.wikipedia.org/wiki/Standing_wave_ratio

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