Differences between dB and dBm

Differences between dB and dBm:
1. dBm
dBm is a unit measuring absolute power. Its calculation formula is: 10 x lgP. (Note: P in this formula equals power (unit: W) divided by 1 mW.
[Example 1]: If the transmit power P is 1 mW, it can be converted to 0 dBm.
[Example 2]: If the power P is 40 W, it can be converted as follows:
10 x lg(40 W/1 mW) = 10 x lg(40000) = 10 x lg4 + 10 x lg10000 = 46 (dBm).
2. dB
dB is a unit measuring relative power. To calculate the difference between two power values such as A and B, use the following formula: 10 x lg(A/B).
[Example 3]: If A is twice as much as B, the formula 10 x lg(A/B) equals 3 dB. That is, A is greater than B by 3 dB.
[Example 4] If A is 46 dBm and B is 40 dBm, A is greater than B by 6 dBm.

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