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Cable and Antenna Troubleshooting Guide – Utilizing Anritsu's Handheld Cable and Antenna Troubleshooting Guide – utilizing Anritsu’s Handheld Site Master™, LMR MasterTM, VNA MasterTM, Cell Master™, or BTS Master™ Antenna Sweeping Antenna Sweeping (continued) Return Loss and VSWR Distance to Fault (DTF) Antenna Isolation Why Sweep Antennas? Maintenance Sweeps Measuring Reflections Comparing Traces For Base Stations Commissioning Sweeps Troubleshooting Sweeps Setting Cable Types Propagation Velocity and Cable Loss For Repeaters Why sweep antennas? Poor VSWR/Return Common Faults Limit Lines Frequency Range Setup Loss can damage transmitters, reduce the Maintenance sweeps can catch faults early, Poor base station antenna isolation allows RF coverage area, and lower data rates. For which will increase network uptime, reduce signals from one base station antenna to leak instance, a return loss of 10 dB means that dropped calls, and allow consistently higher to another. If the leak is 10% of the total power is not radiated and (if data rates. strong enough, BTS the transmitter is still running) that the signal quality can be coverage area is 10% smaller than the Since every cable has a different sweep compromised causing transmitter power settings might imply. signature, it can be difficult to judge changes. But a reference trace, from the commissioning dropped and blocked sweeps, makes it easy to see changes. calls. This sort of problem can affect more Once a problem is spotted, whether from a than just the radios with VSWR alarm or a maintenance sweep, it’s poor isolation. Failures time to troubleshoot the problem. mean that the sector is Troubleshooting sweeps are inherently prone to excessive inter- different from maintenance or commissioning modulation distortion, sweeps, since they require a flexible use of which lowers signal the instrument, calibrations, and settings to Return Loss, or VSWR if you prefer, can be DTF is a way to locate faults identified by quality, increases accurately locate the fault. FlexCal is a BTS used as a one-number screening tool. Return Loss or VSWR measurements. dropped calls, and can Master capability that allows users to change As seen above, the markers for this sweep are Trace comparisons are often used for cause interference with Reduced coverage increases dropped and frequency range without a new calibration, set at the edges of the antenna’s pass band. diagnostics because small changes in cables other radio services. blocked calls due to weak signal areas and which is helpful when troubleshooting. The trace between the markers is better than will have large effects on the DTF trace. network loading imbalances. Base station antenna isolation limits, when Common faults 15.5 dB, (or a VSWR of 1.40) a common limit Because of this, it is accepted practice to take dealing with cellular systems typically should On the data link side, the increased signal for sweeps with an antenna at the far end. include connector, reference sweeps of each cable at be lower than the -50 to -60 dBm range, distortion caused by a low return loss means cable and antenna This trace would typically be accepted as commissioning time for later comparison. although different situations require different that data rates are reduced and capacity faults. When looking good. Reflections are measured using either Changes are often more significant than actual limit numbers. suffers. values. Even so, typical values with a good for faults, it’s VSWR or Return Loss. These are two different Repeaters with insufficient isolation between setup are: Finally, poor Return Loss or VSWR can cause important to know ways to measure the same thing. Return Loss the two antennas are prone to oscillations, transmitter shutdown and even damage, that most faults are is a logarithmic scale, and Voltage Standing Open or Short 0 to 5 dB creating interference that can seriously harm taking out a sector until repaired. connector related. Wave Ratio (VSWR) is a linear scale. Your communications over a wide area. Keeping antenna systems in shape means the This includes loose choice can be made by personal preference, Antenna Better than 16 dB connectors, the unit’s limit numbers are given in, or by Repeaters are tested in system as a whole runs better. Uptime is Connectors Better than 25 dB corroded connectors, and poorly installed company requirements. Here’s the conversion much the same increased, call drops go down, data rates go manner as base connectors. Most formula: Propagation velocity (PV or Vp) directly up, and both managers and customers are stations; however they remaining faults are Return Loss = 20 log |VSWR +1/VSWR-1| affects distance accuracy. PV must be set happier. require better isolation cable related. This —RL/20 -RL/20 either manually or by entering a cable type. VSWR = 1+10 /1-10 Commissioning sweeps provide the basis for includes water in the numbers. Consult your Cable Loss also needs to be set accurately, acceptance of the antenna systems. They cable, loose weather However the quickest conversion is to just repeater installation either manually, or by selecting a cable type. also provide a reference trace for use when wrap, pinched cables, change the instrument units to the preferred instructions for specific False cable loss values can mask Return Loss looking for changes later. For best accuracy, poorly installed settings. guidelines. or VSWR problems. they use a short and a load at the top of the ground kits, bullet Limit lines can be The setup for antenna antenna run. They may also be done with an holes, and even nails created on the Master The frequency range for DTF sweeps should isolation tests uses the antenna attached. in the cable! A small series sweepers and, be set to stay within the load’s bandwidth. If BTS Master, Cell The same data that is used for Return Loss or portion of the faults are antenna related. when, accepted, moved an antenna is used for the load, any portion of Master, or Site VSWR is also used for the Distance to Fault It is possible to damage GPS antennas by from one instrument to the DTF sweep that goes outside of the pass Master’s Two Port (DTF) calculations and display. Users can sweeping. Their active components are not another using a USB band is mostly reflected, reducing the Insertion Loss capability. After a two port change between the two displays at will. This intended to take higher power levels so they stick or Compact Flash accuracy of the vertical axis Return Loss or calibration (An OSLIT cal), the signal source is reduces the number of traces that must be should be replaced by a load (for Return Loss) Memory. This makes looking for faults VSWR measurements. connected to one antenna while the sense archived and tracked by half. or a short (for DTF) before measuring the line. straightforward and helps ensure consistency. A wider frequency range improves distance terminal is connected to the other. The amount of power lost during the transmission Cable loss is also an important commissioning Measurement accuracy is critical. That’s why Return loss, with an antenna on the far end, resolution and lowers the maximum is the antenna isolation. check. Excessive cable loss reduces the there are a variety of calibration routines as should be between 15 to 25 dB. For a line measureable distance. However, if an radiated power, but also, can mask return loss discussed in other parts of this guide. with a load on the far end, the value should antenna is in place at the other end of the Further information on isolation testing can be issues, creating false good readings later. Improper use of the calibration standards, or be between 30 and 40 dB. cable, the DTF frequency range should be found in the application note “Tower Mounted restricted to the antenna’s pass band. GPS location reporting allows verification of use of an antenna sweeper with lower Further information on Return Loss and VSWR Amplifiers, Diagnostics and Isolation the trace location. This validation increases specifications, can lead to inaccurate testing can be found in the application note Further information on DTF testing can be Measurements” and “Practical Tips on the credibility of the measurements and adds measurements and unnecessary equipment “Understanding Cable & Antenna Analysis” at found in the application note “Distance To Transmission Measurements“ at value to the work. replacement due to false fails. What is the www.Anritsu.com. Fault” at www.Anritsu.com www.Anritsu.com. cost of a false fail? Visit us at www.anritsu.com Cable and Antenna Troubleshooting Guide – utilizing Anritsu’s Handheld Site Master™, LMR MasterTM, VNA MasterTM, Cell Master™, or BTS Master™ Tower Mounted Amplifiers (TMAs) Transmission Line Concepts Calibration and Accuracy Which Calibration to Use? Line Sweep Tools (LST) Tower Testing Antenna cables are a type of transmission Antenna and cable sweepers need to be Open, Short, and Load (OSL) Trace Processing TMAs create a larger receive coverage area. line, a cable that has constant impedance calibrated to correct for the very small InstaCal, FlexCal File Transfer If a TMA has low gain, distortion, is in bypass throughout its length. Any change in reflections that will Limit Lines mode, is improperly impedance causes a partial radio signal otherwise lower the Open, Short, Load, Isolation, Through installed, or is reflection. accuracy of the (OSLIT) Line Sweep Tools is a PC based program that completely open, a measurement. The OSL is the most accurate calibration for one port makes life easier for people testing cables and base stations’ receive accuracy of the tests such as Return Loss, VSWR, and DTF. An antennas. It helps with collecting traces, verifying coverage can be instrument depends OSL calibration requires the use of three precision traces, and generating reports in an industry seriously on the accuracy of standards, and is as accurate as the standards.
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