Attenuation and amplification

Attenuation is defined as the reduction of the transmitted energy of a signal in the course of a transmission link. Thus attenuation is negative amplification. Attenuation and amplification are usually specified in dB (decibel). Specifications in dB are „relative levels“. Here the notion „level“ means the comparison between a measured value and a reference value.

The relative level of a transmission link is defined as follows: The level at a reference point, e. g. at the feeding point, is defined as 0 dB, regardless of the actual absolute level. The relative level at the end of the link is derived by adding the reference level and all transmission parameters of the elements of the transmission link (positive for amplifiers, negative for attenuation links).

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Degree of Protection and IP Classification

Standard DIN EN 60529:1991 defines the protection ratings for the housings of electrical appliances. The IP code is used for specifying the protection rating of a housing, e. g.: IP 23 CH; IP = International Protection (Ingress Protection).

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VSWR (Voltage Standing Wave Ratio)

When an electrical line is terminated by a load with its characteristic impedance a signal transmitted to the line is fully absorbed by the matching load. However, if the impedance of the termination differs from the characteristic impedance of the line the wave will be reflected more or less strongly.

The reflection factor r is related to the complex impedance of the line, Z0, and the complex terminating impedance, Z: The waves continuing along the line and reflected waves are overlaying to form standing waves. The amplitude relationship between the largest and the smallest voltage on a lossfree line is defined as the VSWR (Voltage Standing Wave Ratio).

The reflection factor is often specified as the logarithmic value of the return loss: a = -20log(r) dB

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