Cisco AIR-ANT2420V-N= Datasheet download pdf (Page 10)

Increase

Factor

Decrease

Factor

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

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

12 dBm

16 mW

-12 dBm

0.06 mW

13 dBm

20 mW

-13 dBm

0.05 mW

15 dBm

32 mW

-15 dBm

0.03 mW

17 dBm

50 mW

-17 dBm

0.02 mw

20 dBm

100 mW

-20 dBm

0.01 mW

30 dBm

1000 mW (1 W)

-30 dBm

0.001 mW

40 dBm

10,000 mW (10 W)

-40 dBm

0.0001 mW

Outdoor Range

The range of a wireless link is dependent upon the maximum allowable path loss. For outdoor links, this is a

straightforward calculation as long as there is clear line of sight between the two antennas with sufficient clearance

for the Fresnel zone. For line of sight, you should be able to visibly see the remote locations antenna from the main

site. (Longer distances may require the use of binoculars). There should be no obstructions between the antennas

themselves. This includes trees, buildings, hills, and so on.

As the distance extends beyond six miles, the curve of the earth (commonly called earth bulge) affects installation,

requiring antennas to be placed at higher elevations.

Fresnel Zone

Fresnel zone is an elliptical area immediately surrounding the visual path. It varies depending on the length of the

signal path and the frequency of the signal. The Fresnel zone can be calculated, and it must be taken into account

when designing a wireless link (Figure 6).

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Cisco AIR-ANT2420V-N= Datasheet Page 10

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