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dB vs dBc vs dBd vs dBi vs dBm vs dBW | difference between dB dBc dBd dBi dBm dBW

This page compares dB vs dBc vs dBd vs dBi vs dBm vs dBW and mentions difference between dB, dBc, dBd, dBi, dBm and dBW. All these are units of power measurements and dB is used to represent large values by small numeric values for ease of calculations.

dB | Decibel

• dB (Decibel) is unit for measurement of relative power ratios in terms of gain or loss.
• The units are expressed in terms of logarithm to base 10 of a ratio. These ratios are usually expressed in units of watts.
➤ dB= 10 log(P2/P1) or 20 log (A2/A1), Where P2 and P1 are powers and A2/A1 can be two voltage values or two current values.
• Example#1: 10 dB indicates increase or decrease by factor of 10. 20dB indicates increase or decrease by factor of 100 etc.
• Example#2: -3 dB indicates 50% loss where as +3 dB indicates double of power in watts

dBc | deciBels referenced to the carrier

• It is used to express power measurement in logarithmic form with carrier power as reference signal.
• Example#1: Phase noise is typically expressed in units of dBc/Hz, it indicates noise power relative to carrier signal contained in 1 Hz BW centered at certain offset frequency from the desired RF carrier signal.
• Example#2: Harmonics and spurious signals are also represented using dBc such as second harmonics at 12GHz is -50dBc or spurious frequency of 6GHz carrier should be -60dBc etc.

dBd | deciBels referenced to a dipole antenna

• It is used to express power gain measurement in logarithmic form with standard dipole antenna as reference.

dBi | deciBels referenced to an isotropic antenna

• It is used to express power gain measurement in logarithmic form with theoretical isotropic antenna as reference.
• Following equation defines relationship between dBd and dBi.
➤0 dBd = 2.14 dBi

dBm | deciBels referenced to a milli-Watt

• It is used to express power measurement in logarithmic form with 1 mW as reference.
➤PdBm = 10* log10(Pmilliwatt)

dBW | deciBels referenced to a Watt

• It is used to express power measurement in logarithmic form with 1 Watt as reference.
➤PdBW = 10* log10(Pwatt)
• Both dBm and dBW are related with following expression.
➤PdBW = PdBm - 30



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