When we learn about how to calculate RF power to DB, we all learned 3 is the new 2, meaning if RF power is changed by 2 times, DB value will be changed by 3. And of course 1 is 1, and 10 is 10. But there is still a big gap from 2 times multiplexing to 10 times multiplexing, so some time the calculation is still not very easy by just using 1, 3, and 10 in DB value.
Therefore, I believe it's worth remembering another quick reference point, 7 is the new 5, meaning if RF power is changed by 5 times, the DB value should be changed by 7.
Proving:
10Log5=6.9897, close enough to 7
5mw = 10mw / 2 = 10dBm-3 dB = 7dBm
50mw = 100mw / 2 = 20dBm - 3 dB = 17 dBm
or 50mw = (10 x 5) mw = (10 + 7) dBm = 17dBm
this is much better than calculating 50mw as 10 x 2 x 2 x little bit = (10 + 3 + 3 + little bit guees) dBm.
