decibels relative to carrier

dBc (decibels relative to carrier) is a measure of the strength of an instantaneous signal at radio frequency . The dBc increment is based on the decibel , a logarithm ic measure of relative signal strength. Suppose a signal has anunmodulated-carrier power of P ₀ watts and a modulation signal power of P watts at some specified instant intime. Then the instantaneous modulated signal strength in dBc, symbolized S _dBc ,is:

S _dBc = 10 log ₁₀ P / P ₀

Signal strength in dBc can also be calculated in terms of the effectivesignal voltage if the impedance remains constant. Suppose asignal has an unmodulated-carrier root-mean-square ( rms ) voltage of V ₀ volts and a modulated rms signalvoltage of V volts at the same impedance. Then the instantaneous modulatedsignal strength in dBc is:

S _dBc = 20 log ₁₀ V / V ₀

If the dBc figure is positive, then the instantaneous modulated signalstrength is greater than the unmodulated-carrier signal strength. If the dBc figureis negative, then the instantaneous modulated signal strength is less than theunmodulated-carrier signal strength.

Last updated on: Nov 06, 2006

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