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?

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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. accepted manner. It also helps ensure common the Open, Short, pass/fail standards across the organization. compromised. TMA This calibration can and Load (OSL) failure, whether partial be done either at the Trace processing tools in LST include: or complete, reduces used for calibration. instrument test port,  Marker presets – a quick way to make sure the uplink coverage A poor load, cable, or connectors can reduce or at the end of a markers are set to the same place on each area which in turn the calibration accuracy enough to mask phase stable cable, trace. leads to dropped calls. problems with the base station’s antenna and in which case it  File renaming – A quick way to rename TMA failure can also cable run. compensates for the lead to cell load trace file names, titles, and subtitles. It is important to use a phase stable cable length of the cable. imbalances and call  A database – a way to collect groups of when a jumper is needed. While standard This is useful when blocking. traces, say, from one base station, into one cables can be used for jumpers, and even can measuring DTF. One file for ease of forwarding. TMAs can be tested on be calibrated to very good numbers, a side effect of the the tower, which standard cable’s reflections can change when high accuracy OSL calibration is that it is  Report generation – an industry standard verifies the TMA and it is moved or bent. This can change the noise dependent on the frequency span of the antenna report generator. the installation as well tester. If the start and stop frequency is changed, floor by 20 dB or more. A phase stable  Ways to compare traces by overlaying to as saving the time and the OSL cal will need to be redone. jumper cable will remain calibrated when quickly spot changes. With this capability, expense of hiring a tower crew to bring the Changes in impedance, in turn, are caused flexed. InstaCal can be used with the Site Master and Cell trace analysis becomes much simpler. TMA down. by mismatches, or physical changes in the Master. It allows a In addition, LST’s output files can be viewed in the TMA tower testing can be done with the BTS cable, such as: Caring for Precision Cables and quicker OSL style legacy Handheld Software Tools (HHST) software, Master, and many other Anritsu two port calibration with a  Narrow spots, perhaps caused by Connectors ensuring compatibility between users of either testers, which have: clamps, sharp bends, cable stretch, slight loss of Precision cables and connectors are sensitive software tool.  A built-in bias tee, with voltage or other external pressure accuracy. It changes selection, to supply power to the to mishandling. It only takes one mishandled the open, short, and File transfer between the Master series instruments  Change in the internal insulating TMA attachment and detachment to lower the load electronically, making calibration faster. and a PC allows trace validation, report generation, material, the dielectric, for instance, accuracy of a precision connector. and archiving. Transfer can happen several ways.  High RF power mode (0 dBm) for when water gets into the cable FlexCal can be used for troubleshooting tasks at a Mishandling can destroy the accuracy of an Perhaps the simplest is to copy or save the trace to tower testing slight cost in accuracy. FlexCal uses the OSL  Connectors, particularly when OSL calibration standard. either a USB memory stick or  Lower RF power mode (-35 dBm) for calibration, but does the calibration over the full improperly installed, loose or The key is to avoid twisting the body of the a Compact Flash RAM. Data direct gain measurements on the range of the sweeper. This allows users the corroded. connector, making sure that can also be transferred over ground flexibility to change the sweep start and stop that the center pin (gold an USB or Ethernet cable.  A current draw display, to check for  Physical damage such as bullet frequencies as needed to better resolve a fault coated in the picture) does excessive TMA current drain holes or nails without stopping to recalibrate the instrument. Limit lines, either single limits, not rotate when attaching the The term Voltage Standing Wave Ratio or multi-point limits, can be created by LST, as well TMA gain can be measured using the two precision connector. This OSLIT is used for the two port tests. Two port (VSWR) comes from how radio waves are as the Master series cable and antenna testers. port insertion loss measurement. The prevents the formation of tests, as mentioned elsewhere, use a signal distributed along a transmission line. When This is a powerful way to ensure that common procedure is to first measure the TMA noise circular rubbing marks on the source, a device under test, and a measurement reflections are present, a combination of the pass/fail standards are used by everyone involved floor when set up as shown in the illustration. center pin that destroy the of the output of that device. After running an forward (incident) and reflected wave in testing antennas and antenna cables. Then, remove TMA power and take a second accuracy of the connector. OSLIT, it is noise floor reading. The difference between produce a standing wave that forces the RF Precision cables have a minimum bend radius. possible to check the two readings is the gain of the TMA. The voltage to vary with distance. The ratio TMAs, If the cable is bent too tightly, or pinched, the TMA must have a power fail bypass mode for between the high and low voltage in the amplifiers, this to work. transmission center conductor moves closer to the shielding, changing the impedance and filters, antenna When checking TMA gain, it is helpful to save line is the isolation, and causing a reflection. the two traces. This makes it easy to use Voltage many other At this point, the delta markers to measure the difference. It Standing abused cable is no active and also makes it easy to check for in-band Wave Ratio. passive RF longer a precision flatness, pass-band width, and the slope of The log devices. cable. the TMA filters. version of VSWR is called Further information on two port testing can be Further information can be found in the Return Loss. found in the application note “Tower Mounted application note “Tower Mounted Amplifiers, Amplifiers, Diagnostics and Isolation Diagnostics and Isolation Measurements” and Measurements” at www.Anritsu.com. “Practical Tips on Transmission Measurements” at www.Anritsu.com.

® Anritsu. All trademarks are registered trademarks of their respective companies. Data subject to change without notice. For the most recent specifications visit: www.anritsu.com Document No. 11410-00473, Rev B Printed in the United States 2013-03