Off the back of the meeting last night where we were talking about the power output of cards and
antenna gains. I'd thought I'd post how I remember the whacky world of dB gains.
Rule of Thumb: For power gain, every decade of dB adds a zero to the "10".
eg.
0dB = 1
10dB = 10
20dB = 100
30dB = 1000
40dB = 10000
etc.
Rule of Thumb #2: Every doubling of power is +3dB
eg.
100 = 20dB
200 = 23dB
400 = 26dB
etc.
This stems from a formula used to calculate gain in terms of dB,
Av(dB) = 10 log( Av )
Where Av(dB) is the gain in terms of dB, and Av is the raw gain which is determined by
dividing the output power by the input power,
Av=Po/Pi
Also as a side reminder
dBi - Gain of an antenna with respect to a unity-gain isotropic antenna.
dBm - Gain of an amplifier (power output of a transmitter) with respect to 1mW.
Edit: Those wanting to know the dBm of their card, just put the power figure in the formula I mentioned
above (ie. for a 350mW card, 10*log(350)= 25.4dBm)