Adtran TRC6420 User Manual

Section 2  Microwave Path Engineering Basics

TRACER 6420 System Manual

 20

Copyright © 2005 ADTRAN, Inc.

612806420L1-1A

The overall wireless system is directly affected by the antenna selection and installation, discussed in the 
following sections.

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). By ensuring maximum received signal strength, a received signal 
strength indicator (RSSI) helps the equipment installer to determine when alignment is maximized. 

RSSI for the TRACER 6420 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 greater received signal strength and better link performance.

If both the local and remote end of the system are operational, the remote TRACER 6420 receive power 
can be viewed from the local TRACER 6420 VT100 terminal menu interface.

An RSSI test point, located on the front panel, provides a DC voltage level (relative to the 

 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.

Directly related to the subject of antenna alignment is the topic of antenna beam patterns. Antennas used 
with the TRACER 6420 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.