User's Manual

TRACER 4208 System Manual Section 2 Microwave Path Engineering Basics
1. LINE-OF-SITE
The TRACER 4208 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. In addition, 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
Point-to-Point
Wireless communication from a single site to another individual
site. Contrast with point-to-multipoint.
Line-of-Sight
An unobstructed, direct path exists between the transmitting and
the receiving antennas.
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
x
dB
()
(dB)
= 10 ⋅ log
10
x
If the quantity x is referenced to a milliwatt (mW), then the decibel-milliwatt (dBm) is used instead of a
generic decibel.
x
dBm
=
10
⋅
log
10

------
x
-------

(dBm)

1mW

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 if the proposed microwave path is suitable (at a minimum) for
ideal, nondistorted signals before attempting installation.
The fade margin (F ) is a value indicating the amount of extra signal power available to the receiver to
operate at a maximum 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
).
F = P
R
– P
(dB)
sens
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