Alignment

Simplifying the Path Alignment of Microwave Communication Systems:

Wherever microwave links exist, the path between antennas has always required accurateantenna alignment. This process requires highly trained tower crews to physically align theantennas as well as ground technicians and sophisticated, expensive, and complex testequipment to monitor the results. The process of optimizing the transmission path of microwavecommunication systems is about to undergo a significant development in process, simplification and costbenefit without compromising performance or accuracy. The process can now be accomplished with the useof the Path Align-R™ , Models 2200–2241, µwave Antenna Path Alignment Test Sets from PendulumInstruments, formally XL Microwave. Tower installation crews can now perform the entire alignment processthemselves, up the tower, at the antenna, without the need of additional ground technicians, equipment, orindeed, even the waveguides or radios installed.

The Traditional Process:

The traditional process, more typically described as “microwave path alignment,” requires the use of atransmitter and a receiver located at each end of the microwave link. The transmitter generates the signal thatpasses through the transmission line to the antenna, which radiates the signal over the free space link. Thesignal propagates towards the other end of the path and is received by the antenna, forwarding the signalthrough the transmission line to the receiver, connecting the two sites. The receiver processes the signal,producing information on its value relative to the amount that was originally generated at the transmittingend. If the antennas are optimally pointed to each other (aligned), the largest concentration of signal (mainbeam) is emitted and received, reducing the free space attenuation of the signal. Provided the transmissionlines do not lose too much of the signal between the antennas and the radios, maximum signal transfer isachieved. If the antennas are not optimally aligned, then signal transfer is degraded and received dynamicrange is lost.

There are several steps involved in the traditional preparation and process of aligning the antennas of amicrowave communication system. These steps may include making sure the cable or waveguidetransmission line was properly installed, with minimal RF reflection of the microwave signal; that eachantenna polarization is properly setup; and that the transmitter output power is calibrated. A voicecommunication link between the personnel inside the radio room of each site and the tower technicians,located at each antenna, needs to be established using two way mobile radios or cellular phones. Some spreadspectrum radios have an order wire over which to communicate, however, communication to each of thetower technicians will still need to be completed. The engineering profile is reviewed to determine theexpected RSL (receive signal level) for the path under test and any adjustments for output power are applied.Once this setup is complete, the tower technicians are instructed to commence the adjustment of the azimuthalignment (bearing) of the antennas, one at a time. The antennas are panned over their azimuth profile andreadings of the receiver signal output power are taken. Careful observation of the output power reading isnecessary to distinguish the antenna side-lobe to main-lobe response. Once the maximum signal is achieved,the antennas are aligned for elevation optimization. It is evident that the communication between site to siteand tower technician to receiver technician needs to be continuous and clear to ensure that the antennasoptimum alignment setting is achieved.