Line-Of-Sight; Terminology; Decibels; Calculating The Fade Margin - ADTRAN TRACER 6000 SERIES User Manual

Section 2 Microwave Path Engineering Basics
1.

LINE-OF-SIGHT

The TRACER 6200/6320 system is designed for operation in the license-free 5.725 GHz to 5.850 GHz
industrial, scientific, and medical (ISM) band. Radio wave propagation in this band exhibits microwave
characteristics which are ideally suited for point-to-point, line-of-sight communications. Line-of-sight
requires that the transmitting antenna and receiving antenna are able to "see" each other, and that the
straight-line path between the two antennas is free of obstructions such as buildings, trees, mountains, and
in longer paths, even the curvature of the earth. For maximum signal strength, the area around the visual
line-of-sight where microwave signals reflect (Fresnel zone) must also be free of obstructions. Fresnel
zones are discussed in more detail on page 23.

Terminology

Point-to-Point
Line-of-Sight
2.

DECIBELS

Understanding the decibel (dB) format is key when discussing microwave path engineering because the
received signal power is often expressed in decibel format. In general, any quantity can be expressed in
decibels. If the quantity x is a power level (in Watts), the decibel equivalent is defined as
If the quantity x is referenced to a milliwatt (mW), then the decibel-milliwatt (dBm) is used instead of a
generic decibel.
Using the decibel format simplifies power calculations by reducing multiplication and division operations
into addition and subtraction operations.
3.

CALCULATING THE FADE MARGIN

It is imperative to determine whether the proposed microwave path is suitable (at a
minimum) for ideal, nondistorted signals before attempting installation.
The fade margin (F ) is a value in decibels (dB) that represents the amount of signal reduction that can be
tolerated before the link exceeds the specified bit error rate (BER). Fade margin is simply the difference
between the available signal power at the receiver (P
F
16
Wireless communication from a single site to another individual
site. Contrast with point-to-multipoint.
An unobstructed, direct path exists between the transmitting and
the receiving antennas.
⋅
10 log 10 x ( )
x dB =
⎛
⋅
------------ -
x dBm = 10 log 10
⎝
1mW
= P – P
= P + G
R sens T
Copyright © 2005 ADTRAN, Inc.
TRACER 6000 Series Split System Manual
(dB)
⎞
x
(dBm)
⎠
) and the receiver sensitivity (P
R
+ G - L - L - P
T R P sens
).
sens
(dB)
612806320L1-1B