What does dB stand for and mean ?

[romeshkulasekhara]

Why the power gains and voltage gains or power spectral density not specified in simple numbers but only in 'dB's. Does Power spectral density expressed in dB show any ratio of powers?

Thanks.

 

[srizbf]

Re: dB means what

a db itself is a ratio only.
but it is log of that ratio.

so you get different view of the ratio.

the only thing to remember is what is the base reference to which it is calculated .

say , power , 1mW is the comaprison base .... similar you have different base refence.

the base reference is different in audio , rf etc.

srizbf
14thmay2010

 

[LvW]

Re: dB means what

Why the power gains and voltage gains or power spectral density not specified in simple numbers but only in 'dB's. Does Power spectral density expressed in dB show any ratio of powers?

Thanks.

Noise power density is the noise power as measured in a 1 Hz bandwidth.
Therefore, it is NOT given in dB but in dBm/Hz.

 

[snafflekid]

dB means what

Something to note is a Bode plot is a measure of voltage gain, which is a ratio of out to in. So you are finding the ratio of two voltages (which is unitless) then applying a log to it to arrive at dB

Power measurements which divide the power by a reference (1mW for example) and then apply a log are also unitless, but the unit is dBm.

It is a simple matter to take a dBm and convert it back to watts. A dB when converted back to simple gain remains unitless.