ADTRAN 4106 Plan A Network Card User Manual

TRACER 4106/4206 System Manual Section 2 Microwave Path Engineering Basics
612804206L2-1A © 2004 ADTRAN, Inc. 21
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.
The RSSI indicator for the TRACER 4106/4206 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 both the local and remote end of the system are operational, the remote TRACER 4106/4206 receive
power can be viewed from the local TRACER 4106/4206 VT100 terminal menu interface.
An RSSI test point, located on the front panel, provides a DC voltage level (relative to the
GND test point)
that corresponds to the amount of signal being received from the far end's transmitter. 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
Antenna Beam Patterns
Directly related to the subject of antenna alignment is the topic of antenna beam patterns. Antennas used
with the TRACER 4106/4206 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
Verify the antenna installation meets all regulations specified in the National Electric
Code (NEC) Article 810.