| eEngineer - RF Units Conversion |
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Decibel Conversion: Power dB = 10 log [P2/P1] Decibels relative to Power Decibel Conversion: Voltage dB = 20 log [V1/V2] Decibels relative to Voltage across same resistance Decibel Conversion: Current dB = 20 log [I1/I2] Decibels relative to Current through same resistance Decibel Conversion: Milliwatts dBm = 10 log [Signal (mW)/1mW] Decibels relative to one milliwatt Decibel Conversion: Microvolts dBmv = 20 log [Signal (mV)/1mV] Decibels relative to one microvolt across same resistance Decibel Conversion: Microamps dBmA = 20 log [Signal (mA)/1mA] Decibels relative to one microamp through same resistance Power Conversion: dBw to dBm dBm = dBw + 30 Conversion from dBw to dBm. Voltage Conversion: dBv to dBmv dBmv = dBv + 120 Conversion from dBv to dBmv. Voltage to Power Conversion: dBmv to dBm dBm = dBmv - 107 Where the constant 107 is as follows: * RF systems are matched to 50W P = V2 / R 10Log10[P] = 20Log10[V] - 10Log10[50W] V = (PR)0.5 = 0.223 V = 223000 mV For a resistance of 50W and a power of 1 mW: 20Log10[223000mV] = 107 dB Power Density dBw/M2 = 10Log10[V/M - A/M] Decibel-Watts per square meter. dBm/M2 = dBw/M2 + 30 Where the constant 30 is the decibel equivalent of the factor 1000 used to convert between W and mW: 10Log10[1000] = 30 Electric Field to Power Density dBm/M2 = dBmV/M - 115.8 Where the constant 115.8 is as follows: P=|E|2/Zo Where Zo is the free space characteristic impedance (W), equal to 120p. Change this equation to decibels, converting dBW/M2 to dBmW/M2 for power density and dBV/M to dBmV/M for the electric field. This yields 115.8 Electric Field Voltage V/M = 10{[(dBmV/M) -120]/20} Electric Field Voltage in volts per meter Electric Field Current dBmA/M = dBmv/M - 51.5 Where the constant 51.5 is a conversion of the characteristic impedance of free space (120p) into decibels: 20Log10[120p] = 51.5 A/M = 10{[(dBmA/M) -120]/20} Electric Field Current in amps per meter Antenna Factor AFdB = EdB - VrdB where: AF = Antenna Factor in dB/M E = Field strength at the antenna in dBµv/M Vr = Output voltage from receiving antenna in dBµv AF (for 50 W) = 20 log f (MHz) - G(dBi) - 29.78 dB. where f is the measured frequency (MHz), G is the antenna gain (dBi) over isotropic. (E) dBmv/M = (Vo) dBmv + (AF) dB/M AF is the antenna factor of the measuring antenna (as per calibration or per antenna manufacturer). E is the unknown or measured electric field strength. Vo is the adjusted (calibrated for cable & connector losses) spectrum analyzer output. Magnetic Flux Density dBpT = dBmA/M + 2.0 Where the constant 2.0 is as follows: The magnetic flux density B is in Teslas (T) The permeability of the medium is in Henrys per meter (H/M) The permeability in free space is: mo = 4p x 10-7 H/M Convert from T to pT and from A/M to mA/M, and take the Log: 240 - 120 + 20Log10[4p x 10 -7] = 2.0 Conversion Units dB = decibels (Log10) m = milli = 10E-3 m = micro = 10E-6 p = pico = 10E-12 dBw = decibels relative to one watt dBm = decibels relative to one milliwatt dBv = decibels relative to one volt dBmv = decibels relative to one microvolt dBmA = decibels relative to one microamp dBpT = decibels relative to one picoTesla V = Volts A = Amps I = Current R = Ohms (50) W = Watts P = Power H = Henrys T = Teslas AF = Antenna Factor M = Meter |
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