Decibels (dB)

Decibels (dB) is a common unit within the world of radio that’s used to describe a ratio between two signal levels. Unlike normal ratios, dB is not a linear relationship. Instead, it’s logarithmic. Specifically:

• dB = 10 log P1/P0
• 3 dB equals a doubling or halving of the signal
• 10 dB equals a 10x increase or decrease of the signal
• 20 dB equals a 100x increase or decrease of the signal

Signal Loss:

When using this to calculate the signal loss of cables, etc. you simply add the dB’s together. For example, let’s say we have 10 dB input and have a signal loss of 3 dB within a cable. At the output, you would have 7 dB remaining.

Power:

dB can also be used to represent the wattage of a transmitter and is normally denoted as dBm and uses a reference power of 1mW. As a result, the formula is: P1 = 1mw·10dbm/10

The resulting power represented as dBm is:

dBm	Watts
0	0.001
10	0.010
20	0.100
23	0.200
26	0.398
29	0.794
30	1.000
33	1.995
36	3.981
39	7.943
40	10.00
45	31.62
50	100.0