Convert signals from voltage levels to their corresponding decibel equivalents and from decibel levels to their corresponding voltage or current levels?

Answer 1

This question contains a fundamental misunderstanding of a decibel.

A decibel (always shortened to db or dB ) is not a level ; it is a ratio between two levels.

The ratio is not voltages either - it is a power ratio. A power ratio can be converted to a voltage ratio if you understand Ohm's law and if the circuit impedance is the same for both measurements.

To convert a power ratio to dB, take the log of the ratio (to base 10) then multiply by ten. In figures, if ratio is x, calculate 10 log10 (x)

examples:

if power ratio is 10, log(10) is 1, = 10 dB

if power ratio is two, log(2) is .3010, = 3dB.

power ratio 100, 20 dB, 1000 30 db and so on.

It does sometimes seem that db figures are used to define levels. You need to look closely to see how this magic works.

23 dbW is 200 Watts. Because dbW means db relative to 1Watt. More common in electronics is dbm - relative to a milliwatt.

Warning. If you are interested in voltage levels, remember that a 6db increase in power is 4 times the power, but only twice the voltage.

And why is it sometimes dB ? Well, the original scientific unit was the Bel. This was an inconveniently large unit, so engineers started using the deciBel, one tenth of a Bel. Nowadays db seems to be more common than dB.