User Manual

Table Of Contents

Calculating the Link Budget

Version 1.1 - 01/04/00 21

The Fresnel Zone is the expansion of the RF signal radio angles in the vertical plane near

the middle of the RF path. Following is a basic illustration of the Fresnel Zone concept:

The Fresnel radius is calculated as follows:

Calculating Cable Loss

The wireless link is subject to implementation losses such as cable and connector losses.

The two primary coaxial cable specifications for the 300-24 are:

• cable must be 50 ohms nominal impedance

• cable must be of a low loss type

Generally, cable losses are specified in dB/foot or dB/meter. Following is an example of

cable loss ratings:

Notes:

• When you calculate path loss, you should add 1dB at each end of the link to

compensate for connector losses in addition to the cable loss value.

• All cable loss work must be completed by a professional installer.

Formula:

Fresnel Zone Radius =

Cable Type dB/foot dB/meter

LMR400 0.0684 0.220

LMR600 0.0441 0.142

First Fresnel Zone

Line of Sight

Fresnel Radius

Ground

The maximum

Fresnel Radius

indicates that this

path must be kept

clear of

obstructions.

3.4 d

8.12

-----------





× metres

ons

involving cable runs

longer than a few

feet must use high-

quality, low loss

shielded coax.