dB vs. dBm－Mr. Cooooooooooooode

這是從wiki擷取出來的

一直對這兩個名詞很混淆

dB跟dBm到底差在哪?

原來這兩個是可以有公式換算的

dBm: dBm (sometimes dBmW) is an abbreviation for the power ratio in decibels (dB) of the measured power referenced to one milliwatt (mW)

dB: By comparison, the decibel (dB) is a dimensionless unit, used for quantifying the ratio between two values, such as signal-to-noise ratio

這是換算公式:

$x = 10 \log_{10}(1000P)\,$ or, $x = 10 \log_{10}P + 30\,$ and

$P = 10^{(x/10)}/1000 \,$

dBm level	Power	Notes
80 dBm	100 kW	Typical transmission power of FM radio station with 50 km range
60 dBm	1 kW = 1000 W	Typical combined radiated RF power of microwave oven elements
50 dBm	100 W	Typical thermal radiation emitted by a human body
40 dBm	10 W
36 dBm	4 W	Typical maximum output power for a Citizens' band radio station (27 MHz) in many countries
33 dBm	2 W	Maximum output from a UMTS/3G mobile phone (Power class 1 mobiles) Maximum output from a GSM850/900 mobile phone
30 dBm	1 W = 1000 mW	Typical RF leakage from a microwave oven - Maximum output power for DCS 1800 MHz mobile phone Maximum output from a GSM1800/1900 mobile phone
27 dBm	500 mW	Typical cellular phone transmission power Maximum output from a UMTS/3G mobile phone (Power class 2 mobiles)
26 dBm	400 mW
25 dBm	316 mW
24 dBm	250 mW	Maximum output from a UMTS/3G mobile phone (Power class 3 mobiles)
23 dBm	200 mW
22 dBm	160 mW
21 dBm	125 mW	Maximum output from a UMTS/3G mobile phone (Power class 4 mobiles)
20 dBm	100 mW	Bluetooth Class 1 radio, 100 m range (maximum output power from unlicensed FM transmitter). Typical wireless router transmission power.
15 dBm	32 mW	Typical WiFi transmission power in laptops.
10 dBm	10 mW
6 dBm	4.0 mW
5 dBm	3.2 mW
4 dBm	2.5 mW	Bluetooth Class 2 radio, 10 m range
3 dBm	2.0 mW	More precisely (to 8 decimal places) 1.9952623 mW
2 dBm	1.6 mW
1 dBm	1.3 mW
0 dBm	1.0 mW = 1000 µW	Bluetooth standard (Class 3) radio, 1 m range
−1 dBm	794 µW
−3 dBm	501 µW
−5 dBm	316 µW
−10 dBm	100 µW	Typical maximum received signal power (−10 to −30 dBm) of wireless network
−20 dBm	10 µW
−30 dBm	1.0 µW = 1000 nW
−40 dBm	100 nW
−50 dBm	10 nW
−60 dBm	1.0 nW = 1000 pW	The Earth receives one nanowatt per square metre from a magnitude +3.5 star^[1]
−70 dBm	100 pW	Typical range (−60 to −80 dBm) of wireless (802.11x) received signal power over a network
−80 dBm	10 pW
−100 dBm	0.1 pW
−111 dBm	0.008 pW = 8 fW	Thermal noise floor for commercial GPS single channel signal bandwidth (2 MHz)
−127.5 dBm	0.178 fW = 178 aW	Typical received signal power from a GPS satellite
−174 dBm	0.004 aW = 4 zW	Thermal noise floor for 1 Hz bandwidth at room temperature (20 °C)
−192.5 dBm	0.056 zW = 56 yW	Thermal noise floor for 1 Hz bandwidth in outer space (4 kelvins)
−∞ dBm	0 W	Zero power is not well-expressed in dBm (value is negative infinity)