ADTRAN TRACER 5045 - Manual (Page 20)

Section 2 Microwave Path Engineering Basics TRACER 5045 System Manual
20 © 2004 ADTRAN, Inc. 612805045L1-1B
TRACER RSSI Test Points
RSSI 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 both the local and remote end of the system are operational, the remote TRACER 5045 receive power
can be viewed from the local TRACER 5045 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 approximately 0 to 5 VDC. 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 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 2. 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, and 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
main lobe
side lobes