Datasheet

Reference Guide

Figure 6. Fresnel Zone

Based on both line-of-sight and Fresnel zone requirements, Table 3 provides a guideline on height

requirements for 2.4 GHz antennas as various distances. This refers to height above any

obstacles located in the middle of the RF path.

Table 3. Guideline on Height Requirements for 2.4 GHz Antennas

Wireless Link

Distance (miles)

Approx. Value “F” (60% Fresnel

Zone) Ft. at 2.4 GHz

Approx. Value “C”

(Earth Curvature)

Value “H” (mounting Ht.) Ft.

with No Obstructions

1 10 3 13

5 30 5 35

10 44 13 57

15 55 28 83

20 65 50 115

25 72 78 150

Cisco.com provides an Outdoor Bridge Range Calculation Utility for both the 2.4 GHz and 5 GHz

products. This utility calculates the Fresnel zone and maximum range based upon cable types and

lengths, transmitter and receiver models, and antennas. The utility can be found at

http://www.cisco.com/en/US/prod/collateral/wireless/ps5678/ps458/prod_technical_reference0918

6a00800a912a.xls.

A 10 dB fade margin is included for 2.4 GHz calculations, while the included 5dB fade margin

for 5 GHz calculations is sufficient for dependable communications in all weather conditions.

The distances given are only theoretical and should only be used to determine the feasibility

of a particular design.

Outdoors, every increase of 6 dB will double the distance. Every decrease of 6 dB will halve the

distance. Shorter cable runs and higher gain antennas can make a significant difference to the

range.

Regulations

North America

●

Connectors: In 1985, the FCC enacted standards for the commercial use of spread

spectrum technology in the ISM frequency bands. Spread spectrum is currently allowed in

the 900, 2400, and 5200 MHz bands. In 1989, the FCC drafted an amendment governing

spread spectrum systems in the unlicensed ISM band. This amendment is commonly

referred to as the “new” or “’94” rules because it impacts all spread spectrum products

manufactured after June 23, 1994. Products manufactured before June 23 are not affected

by the amendment. Congress enacted this amendment into law in 1990. The FCC 1994