Cisco Aironet 1520 Series User Manual download pdf (Page 9)

Installation

This arrestor is designed to be installed between your antenna cable and the Cisco Aironet access point.

Installation should be indoors, or inside a protected area. A good ground must be attached to the arrestor. This

can be accomplished by attaching a ground lug to the arrestor and using a heavy wire (number 6 solid copper) to

connect the lug to a good earth ground (see Figure 6).

Understanding RF Power Values

Radio frequency (RF) signals are subject to various losses and gains as they pass from transmitter through cable

to antenna, through air (or solid obstruction), to 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

The decibel (dB) scale is a logarithmic scale used to denote the ratio of one power value to another. For example:

X1`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 reduces power by one half, and a decrease of 6 dB results in a one fourth of the

power. Some examples are shown below in Table 1.

Table 1. 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 2 x -3 dB 0.5 x

6 dB 4 x -6 dB 0.25 x

10 dB 10 x -10 dB 0.10 x

12 dB 16 x -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

Power Ratings

WLAN equipment is usually specified in decibels compared to known values. Transmit Power and Receive

Sensitivity are specified in “dBm,” where “m” means 1 milliwatt (mW). So, 0 dBm is equal to 1 mW; 3 dBm is equal

to 2 mW; 6 dBm is equal to 4 mW, and so on, as shown in Table 2.

Table 2. Common mW Values to dBm Values

dBm mW dBm mW

0 dBm 1 mW 0 dBm 1 mW

1 dBm 1.25 mW -1 dBm 0.8 mW

3 dBm 2 mW -3 dBm 0.5 mW

6 dBm 4 mW -6 dBm 0.25 mW

7 dBm 5 mW -7 dBm 0.20 mW

10 dBm 10 mW -10 dBm 0.10 mW

1 2 3 4 5 6 7 8 9 10 11 12 13 14 ... 72 73

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Cisco Aironet 1520 Series User Manual Page 9