User's Manual

TRACER 4108/4208 System Manual Section 2 Microwave Path Engineering Basics
612804208L1-1B © 2003 ADTRAN, Inc. 21
6. ANTENNA INFORMATION
The overall wireless system is directly affected by the antenna selection and installation. The following
sections discuss several factors concerning antenna selection and installation.
Antenna Alignment
With line-of-sight microwave communications, optimum system performance requires that the
transmitting and receiving antennas are properly aligned. This ensures maximum received signal power at
each receiver. Antenna alignment must be achieved in both azimuth (along a horizontal plane) and
elevation (along a vertical plane). A received signal strength indicator (RSSI) aids the equipment installer
in determining when alignment is maximized by simply ensuring maximum RSSI.
TRACER RSSI Test Points
The RSSI indicator for the TRACER 4108/4208 system is provided through the VT100 terminal menus
accessed through the RS-232 interface, and it is presented as a series of bars indicating signal strength.
More bars means more RSSI, which ensures more received signal strength and better link performance.
If the local system has acquired a useful signal from the remote system, then the remote TRACER
4108/4208 RSSI can be viewed from the local TRACER 4108/4208 VT100 terminal menu interface.
An RSSI test point, located on the front panel, represents the voltage (relative to the
GND test point) of a
relative signal level of receive strength from the far end. The voltage at this test point can vary from
approximatly 0 to 5 Volts DC. An RSSI Calibration sheet is shipped with the system to provide the installer
a cross-reference between actual received signal level (in dBm) and RSSI voltage. This sheet is useful for
verifying link budget calculations and ensuring proper equipment installation.
Antenna Beam Patterns
Directly related to the subject of antenna alignment is the topic of antenna beam patterns. Antennas used
with the TRACER 4108/4208 system have a particular beam shape determined in part by the physical
construction and geometry of the antenna. The antenna beam patterns are characterized by a dominant
main lobe, which is the preferred lobe to use for point-to-point communications, and several side lobes, as
shown in Figure 1. When setting up a microwave link, antenna alignment is nothing more than steering the
main lobes of both antennas until the main lobe of one transmitter is centered on the receiving element of
the receiving antenna.
Figure 2. Typical Antenna Beam Pattern
Antennas are also designed to radiate RF energy efficiently for a specific range of frequencies. Please
consult the data sheet for your particular antenna make and model to ensure that it is specified to operate in
the 2400 MHz to 2483.5 MHz frequency band for TRACER 4108 models, and the 5725 MHz to 5850
MHz frequency band for the TRACER 4208 system.