關於dbw 與dbm 的計算

一分貝(dB)表示單元信號強度的相對差異。其比率的基礎對數為10,，如dB = 10 x Log10 (P1/P2)。

基礎10對數規則:

Log10 (AxB) = Log10(A) + Log10(B)

Log10 (A/B) = Log10(A) - Log10(B)

Log10 (1/A) = - Log10(A)

Log10 (0,01) = - Log10(100) = -2

Log10 (0,1) = - Log10(10) = - 1

Log10 (1) = 0

Log10 (2) = 0,3

Log10 (4) = 0,6

Log10(10) = 1

Log10 (20) = 1,3

Log10 (2 x 10) = Log10 (2) + Log10(10) = 1 + 0,3

Log10(100) = 2

Log10 (1000) = 3

Log10 (10000) = 4

對數系統中有如下運算：

1 mW	1 mW/1mW=1	0 dbm = 10 x Log10 (1)
2 mW	2 mW/1mW=2	3 dbm = 10 x Log10 (2)
4 mW	4 mW/1mW=4	6 dbm = 10 x Log10 (4)
10 mW	10 mW/1mW=10	10 dbm = 10 x Log10(10)
0.1 W	100 mW/1mW=100	20 dbm = 10 x Log10(100)
1W	1000 mW/1mW=1000	30 dbm = 10 x Log10 (1000)
10 W	10000mW/1mW=10000	40 dbm = 10 x Log10 (10000)

dbm = dB毫瓦特= 10 x Log10 (電源mW/1mW)

電源	比率	dbm = 10 x Log10 (電源在兆瓦mW/1mW)
1 mW	1 mW/1mW=1	0 dbm = 10 x Log10 (1)
2 mW	2 mW/1mW=2	3 dbm = 10 x Log10 (2)
4 mW	4 mW/1mW=4	6 dbm = 10 x Log10 (4)
10 mW	10 mW/1mW=10	10 dbm = 10 x Log10(10)
0.1 W	100 mW/1mW=100	20 dbm = 10 x Log10(100)
1W	1000 mW/1mW=1000	30 dbm = 10 x Log10 (1000)
10 W	10000mW/1mW=10000	40 dbm = 10 x Log10 (10000)

dbw = dB瓦特= 10 x Log10 (電源W/1W)

電源	比率	dbm = 10 x Log10 (電源W/1W)
1W	1與1 W = 1	0 dbw = 10 x Log10 (1)
2 W	2與1 W = 2	3 dbw = 10 x Log10 (2)
4 W	4與1 W = 4	6 dbw = 10 x Log10 (4)
10 W	10與1 W = 10	10 dbw = 10 x Log10(10)
100 W	0,1與1 W = 0,1	-10 dbw = -10 x Log10(10)
10 W	0,01與1 W = 1/100	-20 dbw = -10 x Log10(100)
1 W	0,001W/1W=1/1000	-30 dbw = -10 x Log10 (1000)

在射頻信號中，0dBm=1mW，每3dB功率信號翻倍，每10dB功率信號變為10倍；對電壓信號，則是每6dB電壓信號翻倍，每20dB電壓信號變為10倍