When it comes to dBm, mw, dB conversion between the three, it is a bit mask, or their own good tidy came to understand the relationship between them.
1. dBm, represents power absolute value calculation formula: 10log (linear power value / 1mw)
For example: 1) the transmit power power = 1mw, the value calculated in units of dBm conversion?
Assignment official: dBmValue = 10log (1mw / 1mw) = 0dBm
2) transmit power power = 40W, the value calculated in units of dBm conversion?
Assignment official: dBmValue = 10log (40000mw / 1mw) = 46dBm (Note: 1W = 1000mw)
2. mw or W, represents the transition between the linear power value, and dBm, the calculation formula: 10 ^ (dBmValue / 10)
For example: 1) dBmValue = 46dBm, the calculated value of the power linearity?
Assignment official: lineraValue = 10 ^ (46/10) = 40000mw = 40W
2) dBmValue = 43dBm, linear value calculated power?
Assignment official: lineraValue = 10 ^ (43/10) = 40000mw = 20W
From the above example can be seen when in dBm, corresponding to the relationship between addition and subtraction, multiplication and division 3dBm 2, i.e. twice the linear value. Because 3dBm converted to a linear value: lineraValue = 10 ^ (3/10) = 2mw.
This relationship can be derived from example 1, dBmValue = 46dBm, linearValue = 10 ^ (43/10) * 10 ^ (3/10) = 20000 * 2 = 40000mw = 40W. Therefore, when the power added 3dBm, for linear, the fact is doubled if the power cut 3dBm for linear, it is actually narrowing doubled.
When dBm to-linear value, which has two relatively simple equation, which is as follows:
A formula: dBmValue + 3dBm = linearValue * 2;
For example: 46dBm + 3dBm = 40W * 2 = 80W.
Official two: dBmValue + 10dBm = linearValue * 10;
For example: 0dBm = 10 ^ (0/10) = 1mw
0dBm + 10dBm = 10^(0 / 10) * 10^(10 / 10) = 1mw * 10mw = 10mw；
10dBm + 10dBm = 10^(10 / 10) * 10^(10 / 10) = 10mw * 10mw = 100mw。
3. dB, a value characterizing the relative value, purely ratio formula: 10log (value1 / value2)
When obtaining dB, dBm - dBm can be obtained directly dB, because:
For example: 30dBm - 0dBm = 30dB, since substituting dB formula: 30dBm - 0dBm = 10log (1000mw / 1mw) - 10log (1mw / 1mw) = 30dB.
