# Difference between dB, dBm and dBi

Forum Coordinator
I was going through the various antenna characteristics and found the usage of many varieties of dB unit!.I would like to know the difference between dB, dBm, and dBi. If anyone can pour some insight that would be helpful.Thanks
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## Comments

• Pune, IndiaForum Coordinator

Hi

The decibel (dB) is one-tenth of the Bel unit and it is a logarithmic unit of measurement of the ratio of two powers, voltages, currents, pressures, etc. Unlike the absolute measurements such as milliWatts, decibels are a relative measurement unit. The "m" in dBm refers simply to the fact that the reference is 1 milliWatt (1 mW) i.e., decibels relative to one milliWatt. Thus, a dBm is a measurement of absolute power. The unit of measurement dBi mainly refers to the gain of an antenna. The 'i' stands for 'isotropic', which points out that the change in power is referenced against an isotropic radiator. An isotropic radiator is an ideal transmitter that radiates useful electromagnetic field in all directions with equal intensity and at 100% efficiency, to a three-dimensional space. This type of antenna does not exist in reality as it is a hypothetical antenna. Still, it’s used as a reference for comparing antenna gains.

• Forum Coordinator
Well!That answered my query. Thank You!🙂
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