The expression dBr is used to define signal strength at RF and AF frequencies. The symbol is an abbreviation for "decibels relative to reference level."

The dBr increment is based on the decibel , a logarithm ic measure of relative signal strength. Suppose a reference signal has a power of *P* _{} watts, and the signal being measured has a power of *P* watts. Then the relative signal strength in dBr, symbolized *S* _{dBr} , is:

*S* _{dBr} = 10 log _{10} *P* / *P* _{}

Signal strength in dBr can also be calculated in terms of the effective signal voltage if the impedance remains constant. Suppose a reference signal has a root-mean-square ( rms ) voltage of *V* _{} volts and the signal being measured has an rms voltage of *V* volts at the same impedance. Then the relative signal strength in dBr is:

*S* _{dBr} = 20 log _{10} *V* / *V* _{}

If the dBr figure is positive, then the measured signal is stronger than the reference signal. If the dBr figure is negative, then the measured signal is weaker than the reference signal.

*This was last updated in*March 2011

*Posted by:*Margaret Rouse

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