dBm - logarithmic power unitdBm – absolute level relative to 1 mW (milliwatt); according to the rules we should use dBmW, however, dBm unit was adopted.
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The unit is commonly used in telecommunications (e.g. access point output power) or used in designing WLAN networks. Expressed in dB, it indicates, how much the power is higher or lower than 1 mW. 0 dB corresponds to 1 mW (milliwatt).
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A commonly used power equation can be used to convert mW into dBm.
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P(ref) – reference value, in this case 1 mW (milliwatt)
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To simplify, the power equation (dBm) is:
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Example Convert 10 mW into dBm:
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The following equation can be used to convert dBm to mW:
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Example Convert 20 dBm into mW (milliwatts).
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Table 1. Converting dBm into mW - wide range -30 dBm | 0,001 mW | -20 dBm | 0,01 mW | -10 dBm | 0,1 mW | 0 dBm | 1 mW | 10 dBm | 10 mW | 20 dBm | 100 mW | 30 dBm | 1000 mW | 40 dBm | 10000 mW | 50 dBm | 100000 mW | 60 dBm | 1000000 mW | 70 dBm | 10000000 mW | 80 dBm | 100000000 mW |
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Table 2. Converting dBm into mW - detailed range 14 dBm | 25,119 mW | 16 dBm | 39,811 mW | 18 dBm | 63,096 mW | 20 dBm | 100,000 mW | 22 dBm | 158,489 mW | 24 dBm | 251,189 mW | 26 dBm | 398,107 mW | 28 dBm | 630,957 mW | 30 dBm | 1000,000 mW |
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Power can be easily converted into voltage: dBm into dBµV and dBmV. However, the internal impedance must be known to convert power to voltage. DVB-T, cable or industrial television systems use 75 Ohm impedance. Radio systems use 50 Ohm impedance.
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Equations for those two environments are given below:
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dBmV = 46,9897 + dBm (@ 50 ohm) dBmV = 48,7506 + dBm (@ 75 ohm)
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Example Converting 15 dBm into dBmV (for 50 Ohm impedance)
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dBmV = 46,9897 + 15 = 61,9897 dBmV
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dBµV = 106,98 + dBm (@ 50 ohm) dBµV = 108,75 + dBm (@ 75 ohm)
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Example Converting 20 dBm into dBµV (for 50 Ohm impedance)
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dBµV = 106,98 + 20 = 126,98 dBµV
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