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I have a question , why decibels are useful for electrical engineers ?? I still can't figure out why it is useful to use decibels in expressing power ratios , gain and other things ?

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  • \$\begingroup\$ It nit because they don’t know about Napers which is the units of log exponents, discovered centuries ago, it’s because a lot of natural physics including attenuation spans so many decades that it appears linear on a log-log scale. \$\endgroup\$ Commented Feb 12, 2019 at 13:23
  • \$\begingroup\$ It isn't more "useful" than percentages, or ratios, or fractions. It's just more practical in a lot of cases, mainly because the scale is logarithmic, unlike the other alternatives I gave. \$\endgroup\$
    – dim
    Commented Feb 12, 2019 at 13:24
  • \$\begingroup\$ The sun provides about +250 dBm of power. Yet Boltzmann, using measurements of the thermal energy of molecules, found the thermal noise floor, at one vibration per second, to be about -174dBm. In between those two power levels, life is exciting. \$\endgroup\$ Commented Feb 12, 2019 at 17:49

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Because gain in linear systems, as a function of frequency, tends to vary asymptotically on a log-log scale, and that helps greatly with visualisation.

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Just as an example,take the case of human hearing. The range of levels that the ear can perceive range when expressed in dB range from 0 (threshold of hearing sensitivity) to about 150 (close to a jet engine at full throttle). To express either of these numbers in decimal format would require many zeroes and be difficult to interpret. Another example is trying to determine an overall gain (or attenuation) for many individual stages. With dB, it is only necessary to add the dB value of each stage. Without dBs, you have to multiply many numbers with varying amounts of zeroes. It is much more difficult and prone to errors. Many other examples exist but I hope you get the idea.

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