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Decibel Conversion


The decibel (dB) represents a logrithmic ratio between two quantities and is unitless. If the ratio is refered to a specific quantity this is indicated by a suffix (dBm is referenced against 1 mW and dBV is 1 Volt).

Originally the dB was for power ratios, given by dB=10 log (P1/P2)

Power is proportional to voltage squared, hence the ratio of voltages or currents across a constant impedence is given by dB=20 log(V1/V2) or 20 log(I1/I2)


dBPower Ratio
(10 log)
Voltage/Current
Ratio
(20 log)
dBPower Ratio
(10 log)
Voltage Current
Ratio
(20 log)
01.01.001.01.0
32.01.4-30.500.71
64.02.0-60.250.50
1010.03.2-100.100.32
1216.04.0-120.050.25
1425.05.0-140.040.20
2010210-2010-20.10
3010332-3010-30.03
40104102-4010-410-2
60106103-6010-610-3
80108104-8010-810-4
1001010105-10010-1010-5
1201012106-12010-1210-6
1401014107-14010-1410-7
Simple rule of thumb:
When working with power, 3 dB is twice, 10 dB is 10 times; When working with voltage or current, 6 dB is twice, 20 dB is 10 times
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