RF Power Levels – dBm and dBW

dBm and dBW are widely used to measure absolute power levels in RF engineering

The ratio of two RF power (or voltage) levels can be expressed in dB. This is a dimensionless quantity and does not provide any information about the actual (or absolute) power levels involved, only the relative levels. A more useful way of comparing power (or voltage) levels is to reference them to a standard power level.

For low-power systems, such as those used in mobile communications, the dBm (decibel-milliwatt) scale is a convenient reference power level, in which power is referenced to a level of 1 mW:

\(P \:(dBm) = 10\log\bigg(\displaystyle \frac{P\:(mW)}{1\:mW}\bigg)\)

For high-power systems, such as those used in satellite communications, the dBW (decibel-watt) scale is commonly used, in which power is referenced to 1 W:

\(P \:(dBW) = 10\log\bigg(\displaystyle \frac{P\:(W)}{1\:W}\bigg)\)

Therefore, a power level of 10 W (or 10,000 mW), is expressed as +40 dBm when referenced to 1 mW or +10 dBW when referenced to 1 W.



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