ADTRAN 12804108L1A System Manual

TRACER 4108/4208 System Manual Section 2 Microwave Path Engineering Basics612804208L1-1B © 2003 ADTRAN, Inc. 216. ANTENNA INFORMATIONThe overall wireless system is directly affected by the antenna selection and installation. The followingsections discuss several factors concerning antenna selection and installation.Antenna AlignmentWith line-of-sight microwave communications, optimum system performance requires that thetransmitting and receiving antennas are properly aligned. This ensures maximum received signal power ateach receiver. Antenna alignment must be achieved in both azimuth (along a horizontal plane) andelevation (along a vertical plane). A received signal strength indicator (RSSI) aids the equipment installerin determining when alignment is maximized by simply ensuring maximum RSSI.TRACER RSSI Test PointsThe RSSI indicator for the TRACER 4108/4208 system is provided through the VT100 terminal menusaccessed 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 TRACER4108/4208 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 arelative signal level of receive strength from the far end. The voltage at this test point can vary fromapproximatly 0 to 5 Volts DC. An RSSI Calibration sheet is shipped with the system to provide the installera cross-reference between actual received signal level (in dBm) and RSSI voltage. This sheet is useful forverifying link budget calculations and ensuring proper equipment installation.Antenna Beam PatternsDirectly related to the subject of antenna alignment is the topic of antenna beam patterns. Antennas usedwith the TRACER 4108/4208 system have a particular beam shape determined in part by the physicalconstruction and geometry of the antenna. The antenna beam patterns are characterized by a dominantmain lobe, which is the preferred lobe to use for point-to-point communications, and several side lobes, asshown in Figure 1. When setting up a microwave link, antenna alignment is nothing more than steering themain lobes of both antennas until the main lobe of one transmitter is centered on the receiving element ofthe receiving antenna.Figure 2. Typical Antenna Beam PatternAntennas are also designed to radiate RF energy efficiently for a specific range of frequencies. Pleaseconsult the data sheet for your particular antenna make and model to ensure that it is specified to operate inthe 2400 MHz to 2483.5 MHz frequency band for TRACER 4108 models, and the 5725 MHz to 5850MHz frequency band for the TRACER 4208 system.