DBm

From Free net encyclopedia

dBm is an abbreviation for the power ratio in decibel (dB) of the measured power referenced to one milliwatt (mW). It is used in radio, microwave and fiber optic work as a convenient measure of absolute power because of its capability to express both very large and very small values in a short form. dBm (or dBmW) and dBW are independent of impedance.

Since it is referenced to the watt, it is an absolute unit, used when measuring absolute power. It should not be confused with dB, a dimensionless unit, which is used when measuring the ratio between two values, such as SNR.

1 Unit conversion
2 See also
3 Source
4 External links

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Unit conversion

Zero dBm equals one milliwatt. A 3 dBm increase represents roughly doubling the power, which means that 3 dBm equals roughly 2 mW. For a 3 dBm decrease the power is reduced by about one half, making −3 dBm equal to about 0.5 milliwatt. To express an arbitrary power P as x dBm, or go in the other direction, the equations

<math>

x = 10 \log_{10}(P / (1 \ \mathrm{mW})) </math> and

<math>

P =(1 \ \mathrm{mW}) 10^{(x/10)} </math>, respectively, should be used. Below is table summarizing useful cases:

dBm level	Power
80 dBm	100000 W	Typical transmission power of FM radio station
60 dBm	1000 W	Typical RF power inside microwave oven
40 dBm	10 W
36 dBm	4 W
30 dBm	1 W	Typical RF leakage from microwave oven
27 dBm	500 mW	Typical cellular phone transmission power
26 dBm	400 mW
25 dBm	320 mW
24 dBm	250 mW
23 dBm	200 mW
22 dBm	160 mW
21 dBm	125 mW
20 dBm	100 mW
15 dBm	32 mW
10 dBm	10 mW
5 dBm	3.2 mW
4 dBm	2.5 mW
3 dBm	2.0 mW
2 dBm	1.6 mW
1 dBm	1.3 mW
0 dBm	1.0 mW
−1 dBm	0.79 mW
−5 dBm	0.32 mW
−10 dBm	0.1 mW
−20 dBm	0.01 mW
−30 dBm	0.001 mW
−40 dBm	0.0001 mW
−50 dBm	0.00001 mW
−60 dBm	0.000001 mW
−70 dBm	0.0000001 mW
−80 dBm	0.00000001 mW
−127.5 dBm	0.00000000000018 mW	Typical received signal power from GPS satellite
−infinity dBm	0 mW