dBm、dBuV及dBmV都是绝对单位,即代表某一物理量,相关换算表如下(阻抗以50Ω为例):
dBm |
mW |
uV |
dBuV |
dBmV |
-30 |
0.001 |
7071.07 |
76.9897 |
16.9897 |
-25 |
0.003 |
12574.33 |
81.9897 |
21.9897 |
-20 |
0.010 |
22360.68 |
86.9897 |
26.9897 |
-15 |
0.032 |
39763.54 |
91.9897 |
31.9897 |
-10 |
0.100 |
70710.68 |
96.9897 |
36.9897 |
-5 |
0.316 |
125743.34 |
101.9897 |
41.9897 |
0 |
1.000 |
223606.80 |
106.9897 |
46.9897 |
5 |
3.162 |
397635.36 |
111.9897 |
51.9897 |
10 |
10.000 |
707106.78 |
116.9897 |
56.9897 |
15 |
31.623 |
1257433.43 |
121.9897 |
61.9897 |
20 |
100.000 |
2236067.98 |
126.9897 |
66.9897 |
25 |
316.228 |
3976353.64 |
131.9897 |
71.9897 |
30 |
1000.000 |
7071067.81 |
136.9897 |
76.9897 |
因此-30dBm对于0.001mW、或10-6 W。在50Ω负载上上为7071.07uV,或0.007071mV。上表的公式及推导方式如下:
至于dB及dBc为相对单位。就功率而言,差100dB等于差20倍。
问题:0dBm与-50dBm相差50dB或50dBm?
回答:50dB。0dBm=1mW,-50dBm=10-5mW,兩者相差105倍,等于50dB。或者两者相差0.99999mW,而0.99999mW等於-0.0000434dBm≈0dBm。50dBm=105mW=100W,显然不能为50dBm。