Tracer Rssi Test Points, Antenna Beam Patterns

TRACER 5045 System Manual	Section 2 Microwave Path Engineering Basics

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.

main lobe

side lobes

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.

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