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TRACER 4106/4206 System Manual Section 2 Microwave Path Engineering Basics

7. OTHER CONSIDERATIONS

Path Availability

The path availability of a wireless link is a metric that expresses the fractional amount of time a link is

available over some fixed amount of time, and depends on several factors. Path availability is expressed as

where the parameters are

a terrain factor

b climate factor

f carrier frequency (GHz)

d path length (miles)

F fade margin (dB)

Terrain Factor (a)

The terrain factor is a quantity that compensates the link availability for different types of terrain.

Generally speaking, the more smooth an area's terrain is, the less availability a wireless link running over

that terrain will have, primarily due to multipath reflections. In contrast, secondary microwave signals will

be randomly dispersed over rough terrain, and will not interfere with the main signal lobe as badly as in the

smooth terrain case. The terrain factor values normally used are listed below:

Climate Factor (b)

The climate factor is a quantity that compensates the link availability for different types of climates

(weather). In general, microwave links operating in areas with high humidity will have less availability

than those in arid areas, primarily because water is a dispersive mechanism to microwave energy, and

causes the main signal lobe to refract and disperse away from the receiver location. The climate factor

28 220 177

30 239 195

32 259 213

34 279 232

36 300 252

Terrain Terrain Factor Description

Smooth 4 water, flat desert

Average 1 moderate roughness

Mountainous 1/4 very rough, mountainous

Table 5. Minimum Antenna Height for Given Path Lengths (Continued)

Path Length

(miles)

Min. Antenna Height

@ 2.4 GHz

(ft)

Min. Antenna Height

@ 5.8 GHz

(ft)

A12.510

6–

()abfd

F10

⁄

–

()–[]100%

(%)

1 2 ... 18 19 20 21 22 23 24 25 26 27 28 ... 59 60

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