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TRACER 5045 System Manual Section 2 Microwave Path Engineering Basics
612805045L1-1A © 2003 ADTRAN, Inc. 21
TRACER RSSI Test Points
The RSSI indicator for the TRACER 5045 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 5045
RSSI can be viewed from the local TRACER 5045 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 greater than 4 Volts DC, with 0 Volts corresponding to no signal and 4 Volts or better to
full signal strength.
Antenna Beam Patterns
Directly related to the subject of antenna alignment is the topic of antenna beam patterns. Antennas used
with the TRACER 5045 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 5725 MHz to 5850 MHz frequency band for the TRACER 5045 system.
Fresnel Zones, Earth Curvature, & Antenna Heights
Fresnel zones correspond to regions in the microwave path where reflections of the intended signal occur
and combine in both constructive and destructive manners with the main signal, thereby either enhancing
or reducing the net power at the receiver.
In general, the odd numbered Fresnel zones (1, 3, 5, ...) add constructively at the receiver, while the even
numbered Fresnel zones (2, 4, 6, ...) add destructively at the receiver.
main lobe
side lobes