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## VK3KHB## RF Power Loss / Gain Calculator |

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What is dBm?A logarithmic ratio of power levels with a base reference set to 1mW = 0 dBm. With a known impedance value you can convert any voltage V to dBm and vice versa. The calculator / chart lets you find out only Z, L or V and once known W can also be given. Remember to clear the inputs to get correct figures. |

RF Power - Loss Formulae, Calculator and Chart. The example below uses a 3dB loss in a transmission line of a 10 watt transmitter, resulting in ~5 watts being presented to the antenna for emission, follow the transposition steps to understand how it is calculated...

Power to dB and dB to Power: (P1 = ref compare / P0 = ref base) Transposed Step 1 (divide b.s. by 10) Step 2 (Anti-log) Step 3 for P1 (multi b.s. by P0) - or - 3 for P0 (divide b.s. by P1) - or - 3b for P0 (invert b.s.) | dB = 10 log (P1 / P0) dB/10 = log (P1 / P0) Alog(dB/10) = (P1 / P0) P0* (Alog(dB/10)) = P1 (Alog(dB/10)) / P1= 1 / P0 1 / (Alog(db/10) / P1) = P0 |

Loss of Power e.g. -3.01 = 10 log (5 /10) -0.301= log (5/10) Alog(-0.301) = (5/10) 10 * (0.5) = 5 Alog(-0.301) / 5 = 1/10 1 / Alog(-0.301)/5) = 10 | Gain of Power e.g. +3.01 = 10 log (10/5) 0.301 = log (10/5) Alog(0.301) = (10/5) 5 * 1.9998 = 10 Alog(0.301) /10 = 1/5 1 / (Alog(0.301) /10) = 5 |

73

Gary, VK3KHB