Cisco AIR-ANT2420V-N= Fiche technique télécharger pdf (Page 9)

Figure 5. Cisco Aironet Lightning Arrestor

The accepted IEEE transient (surge) suppression is .000008 seconds (8 micro seconds). The Cisco Aironet

Lightning Arrestor is a 50-ohm transmission line with a gas discharge tube positioned between the center

conductor and ground. This gas discharge tube changes from an open circuit to a short circuit almost

instantaneously in the presence of voltage and energy surges, providing a path to ground for the energy surge.

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

1 2 3 4 5 6 7 8 9 10 11 12 13 14 ... 87 88

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