0 + 0 = 3

One of my favorite questions to ask to a new DAS engineer during interview is what is 0 dBm + 0 dBm. Say what? Answer is 3 dBm. And here's how:

0 dBm = 1 milliwatt

So 0 dBm + 0 dBm = 1 milliwatt + 1 milliwatt = 2 milliwatt

2 milliwatt = 10* Log(2) = 3 dBm

Therefore, 0 dBm + 0 dBm = 3 dBm.