dBm

dBm or dBmW (decibel-milliwatts) is a unit of power level expressed using a logarithmic decibel (dB) scale respective to one milliwatt (mW).

It is commonly used by radio, microwave and fiber-optical communication technicians & engineers to measure the power of system transmissions on a log scale, which can express both very large and very small values in a short form.

dBW is a similar unit measured relative to one watt (1,000 mW), rather than a milliwatt.

[3]: 7.4 In audio and telephony, dBm is typically referenced relative to the 600-ohm impedance[4] commonly used in telephone voice networks, while in radio-frequency work dBm is typically referenced relative to a 50-ohm impedance.

Conversely, to express an arbitrary power level x in dBm, as P in mW:

Below is a table summarizing useful cases: Typical maximum output RF power from a ham radio HF transceiver without power amplifier Maximal output from a GSM850/900 mobile phone DCS or GSM 1,800/1,900 MHz mobile phone.

Also, maximal power allowed by the FCC for American amateur radio licensees to fly radio-controlled aircraft or operate RC models of any other type on the amateur radio bands in the US.

In European practice, psophometric weighting may be, as indicated by context, equivalent to dBm0p, which is preferred.

In audio, 0 dBm often corresponds to approximately 0.775 volts, since 0.775 V dissipates 1 mW in a 600 Ω load.

[16] The corresponding voltage level is 0 dBu, without the 600 Ω restriction.

In general the relationship between the power level P in dBm and the RMS voltage V in volts across a load of resistance R (typically used to terminate a transmission line with impedance Z) is:

[17] This article incorporates public domain material from Federal Standard 1037C.