What is "electromagnetic noise" that corrupts data?
Decibel was about levels of noise What do we mean 90db weakening?
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Your question is quite vague. Please provide some context to your question. A decibel is a ratio, it is not specific to noise.– Ron TrunkCommented Apr 15, 2019 at 19:10
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I have read that we use fiber optics when there is "excessive electromagnetic noise (like in industries)" .What does that mean?What "noise"?– Some1Commented Apr 15, 2019 at 19:12
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Just a terminology comment: When engineers talk of "signal" and "noise": "signal" means the good signal, the stuff they want, "noise" is everything else. It doesn't (in this context) mean acoustic noise.– jonathanjoCommented Apr 16, 2019 at 12:22
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1 Answer
Conductive cables pick up stray magnetic fields from the environment and convert them to voltage (induction). This voltage disturbs the data signal as noise and, depending on the level, makes it harder or even impossible to read back the data. The lower the noise level the better, usually expressed as signal-to-noise ration (SNR). 90 dB is a good SNR ratio and means that the signal is one billion times stronger than the noise (10^(90/10)).
In fiber there's no induction, so there's no noise from external fields (practically at least).
Another problem with any kind of cabling is attenuation - the signal loses power and its level simply becomes lower the longer the cable is (or the lower its quality is). 90 dB attenuation or power loss would mean the signal strength is one billionth of what was sent.