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DBw is a unit representing the absolute value of power (based on 1W power, dBm is based on 1mW).
[Example] If power P is 1w, it will be 0dBw after being converted to dBw.
In a word, dB, dBi, dBd and dBc are the ratios between two quantities, representing the relative size between two quantities, while dBm and dBw are the absolute values of power. In the calculation of dB, dBm and dBw, pay attention to the basic concepts. When one dBm (or dBw) is subtracted from another dBm (dBw), the result is dB, for example: 30dBm - 0dBm=30dB.
Generally speaking, in engineering, there is only addition and subtraction between dBm (or dBw) and dBm (or dBw) without multiplication and division. The most frequently used method is subtraction: dBm minus dBm is actually the division of two powers, signal power and noise power Division is Signal-to-noise ratio (SNR) 。 
