By XL Microwave, Inc. Wherever microwave links exist, the path between antennas has always required accurate antenna alignment. This process requires highly trained tower crews to physically align the antennas as well as ground technicians and sophisticated, expensive, and complex test equipment to monitor the results. The process of optimizing the transmission path of microwave communication systems is about to undergo a significant development in process, simplification and cost benefit without compromising performance or accuracy. The process can now be accomplished with the use of the new Path Align-R™ , Model 2200, mwave Antenna Path Alignment Test Set from XL Microwave. Tower installation crews can now perform the entire alignment process themselves, up the tower, at the antenna, without the need of additional ground technicians, equipment, or indeed, even the waveguides or radios installed.
The Traditional Process
The traditional process, more typically described as "microwave path alignment," requires the use of a transmitter and a receiver located at each end of the microwave link. The transmitter generates the signal that passes through the transmission line to the antenna, which radiates the signal over the free space link. The signal propagates towards the other end of the path and is received by the antenna, forwarding the signal through 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 transmitting end. If the antennas are optimally pointed to each other (aligned), the largest concentration of signal (main beam) is emitted and received, reducing the free space attenuation of the signal. Provided the transmission lines do not lose too much of the signal between the antennas and the radios, maximum signal transfer is achieved. If the antennas are not optimally aligned, then signal transfer is degraded and received dynamic range is lost.
There are several steps involved in the traditional preparation and process of aligning the antennas of a microwave communication system. These steps may include making sure the cable or waveguide transmission line was properly installed, with minimal RF reflection of the microwave signal; that each antenna polarization is properly setup; and that the transmitter output power is calibrated. A voice communication 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 spread spectrum radios have an order wire over which to communicate, however, communication to each of the tower technicians will still need to be completed. The engineering profile is reviewed to determine the expected 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 azimuth alignment (bearing) of the antennas, one at a time. The antennas are panned over their azimuth profile and readings of the receiver signal output power are taken. Careful observation of the output power reading is necessary 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 site and tower technician to receiver technician needs to be continuous and clear to ensure that the antennas optimum alignment setting is achieved.
Traditionally, the radios that will be placed at each site are used to complete the task of optimizing the path. However, there are several reasons for not utilizing the radios to complete the process. The radios may not be available at the time the test has been scheduled or their reliability may be questionable, thus alternate methods are needed. Another possible reason the radios might not be able to be used is that the FCC permits have not been granted, but the contractor needs to complete the path test on time to meet the customer's requirements, or ahead of expected turbulent weather. In addition, if the anticipated path is questionable, a quick, cost effective, reliable method is needed to test the link, prior to the significant investment of constructing towers, purchasing radios and other expensive equipment and hardware, etc.
Alternative test instrumentation must be utilized, in lieu of the radios, whenever the previously mentioned circumstances arise. Scheduling of the path alignment test and installation of the associated hardware (cables, waveguide, antenna, etc.) can be facilitated to reduce excess mobilization costs. Some of the most widely used equipment for this application are signal generators (used as the transmitter) and spectrum analyzers (used as the receiver). The signal generator should be a broadband, synthesized device (phase locked to a reference clock) with accurate output power, equal to or greater than 0 dBm. The spectrum analyzer should be tunable, and have at least –100 dBm of sensitivity at the frequency band of interest. Signal acquisition speed of the receiver is essential to quickly spot subtle changes in antenna response or to support investigation of problem paths. Most importantly, ease of use is vital in order to reduce the training costs of test technicians. Much of the test equipment used in this alternate method of path alignment tends to be expensive and complicated.
Application Specific Solution
Recent test instrumentation has brought on feature rich, expensive systems that shoot for the stars in offering the latest and greatest in technology. However, these systems are mostly not fit, nor are they practical, for specific applications such as antenna path alignment. The most successful new instrumentation in the industry has been equipment that is application specific, portable, battery powered, and easy to use, without compromising performance. The Path Align-R™, by XL Microwave, is a new addition to this practical, application specific category. It is specifically designed for use as a microwave path alignment test set. Among its many features and functions, eight specific traits fit those identified as important to microwave antenna path alignment.
It is apparent that the Path Align-R™ test set is well featured to offer impressive results in accomplishing the goal of an optimum solution for the microwave path alignment test process.
Simplifying the Process
We have laid the groundwork for establishing the Path Align-R™ test set as a viable and effective solution for the path alignment process. We will now describe how this process of aligning the microwave link is greatly simplified.
The difficulties of scheduling an antenna alignment test with the radios can cause significant delays, as described earlier. Furthermore, traditional test methods can produce significant costs in mobilization, deployment and testing of the antenna system. If the transmission lines (waveguides, etc.) connecting the antenna to the radio were to have a problem, the test is in jeopardy until they are corrected. If the path under test is questionable (due to site choice, obstructions, etc.), the Path Align-R™ can step right in with minimal effort to verify if there are any problems. Using the Path Align-R™ test set, the overhead associated with offering path alignment services (cost of equipment, level of expertise required, and training time) has been greatly reduced. Offering path alignment services with the Path Align-R™ translates to providing more revenue opportunities for your company.