Appendix II: Understanding RF Power Values

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Radio Frequency signals are subject to various losses and gains as they pass from the transmitter through the cable to the antenna, through the air (or solid obstruction), to the receiving antenna, cable and receiving radio. With the exception of solid obstructions, most of these figures and factors are known and can be used in the design process to determine whether an RF system such as a WLAN will work.

Decibels (dB)

Decibel measurements are found in the electronics, audio and telecommunications fields. They have wide applicability because they are not measurable quantities of anything; they simply represent two signal power ratios. When a decibel figure is positive, then the second signal is stronger than the first signal. When the decibel figure is negative, then the second signal is weaker than the first signal.

The Decibel (dB) scale is a logarithmic scale denoting the ratio of one power value to another—for example:

• dB = 10 log10 (Power A/Power B)

An increase of 3 dB indicates a doubling (2x) of power. An increase of 6 dB indicates a quadrupling (4x) of power. Conversely, a decrease of 3 dB is a halving (1/2) of power, and a decrease of 6 dB is a quarter (1/4) the power. Some examples are shown in the table below.

Decibel Values and Corresponding Factors

Increase	Factor	Decrease	Factor
0 dB	1 x (same)	0 dB	1 x (same)
1 dB	1.25 x	-1 dB	0.8 x
3 dB	2x	-3 dB	0.5 x
6 dB	4x	-6 dB	0.25 x
10 dB	10x	-10 dB	0.10x
12 dB	16x	-12 dB	0.06 x
20 dB	100 x	-20 dB	0.01 x
30 dB	1000 x	-30 dB	0.001 x
40 dB	10,000 x	-40 dB	0.0001 x

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