Difference between dB, dBw vs dBm

Decibel(dB):
dB = 10 log10 (x)
For example, amplifier gain is Pout/Pin=G
So Gain in dB = G(dB) = 10 log10 G

dBw (dB watt):
dBw = 10 log10 (P/1W)

dBm (dB milliwatt):
dBm = 10 log10 (P/1mW)

Likewise, P(dBm)=0dBm is P=1mW; P(dBw)=-30dBw is P=1mW.


What’s more, we have to remember the following:

10log10[10^n]=10n

Therefore, if we express gain as G=10^n, we conclude

G=10^n    equal to     G(dB)=10n

10log10[2^n]=3n

Therefore, if we express gain as G=2^n, we conclude

G=2^n     equal to     G(dB)=3n


PS:     1   is   0dB
0   is -infinite dB
5^n   is 7n dB

BTW, sometimes we need to convert dBm to mW or Vrms or Vpeak or Vpp.
Please read the PDF file or search the web. Then you can get the desired value.

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