Справочник Пользователя для Adtran TRC6420
Section 2 Microwave Path Engineering Basics
TRACER 6420 System Manual
14
Copyright © 2005 ADTRAN, Inc.
612806420L1-1A
1.
LINE-OF-SIGHT
The TRACER 6420 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 21.
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 21.
Terminology
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
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.
generic decibel.
Using the decibel format simplifies power calculations by reducing multiplication and division operations
into addition and subtraction operations.
into addition and subtraction operations.
3.
CALCULATING THE FADE MARGIN
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
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
R
) and the receiver sensitivity (P
sens
).
Point-to-Point
Wireless communication from a single site to another individual
site. Contrast with point-to-multipoint.
site. Contrast with point-to-multipoint.
Line-of-Sight
An unobstructed, direct path exists between the transmitting and
the receiving antennas.
the receiving antennas.
It is imperative to determine whether the proposed microwave path is suitable (at a
minimum) for ideal, nondistorted signals before attempting installation.
minimum) for ideal, nondistorted signals before attempting installation.
xdB
10 log10 x
( )
⋅
=
(dB)
xdBm
10 log10
x
1mW
-------------
⎝
⎠
⎛
⎞
⋅
=
(dBm)
F
PR Psens
–
=
(dB)
= P
T
+ G
T
+ G
R
- L - L
P
- P
sens