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Handheld Users Group

Handheld Users Group

Delivering leading solutions for today's field and maintenance challenges

 
Interference hunter


With over 20 years leading the way in handheld testing Anritsu has a well earned reputation for superior measurements in not so superior conditions. learn more about the very latest handheld testing technology.

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Troubleshooting PIM Problems in the Field

Passive Intermodulation (PIM) testing is becoming more important as cellular systems age and the carrier count increases. A test that was not as important when cellular systems were lightly loaded is now a critical part of modern cellular maintenance.
PIM comes from two or more strong RF signals mixing in a non-linear device. These non-linear devices, or junctions, occur in improperly tightened, damaged, or corroded connectors or in damaged antennas. Rusty components, such as mounts and bolts, are also suspect when hunting for PIM sources.


Construction Methods
Avoiding PIM starts with quality construction methods. However, increasing capacity, new services, and aging infrastructure are all working against this strategy. It is apparent that most on-site PIM issues that affect service are derived from the sidebands of internally generated interference, not the frequencies themselves.
It is essential to have the correct termination tools with PIM testing. Calibrated torque wrenches should be used when justified. Because cleanliness is key, alcohol wipes are necessary to clean every step of the termination process.
Care must be exercised when PIM testing. A large number of faults are caused by over testing and by damage from repeated torque. Connectors are generally weak in their mounting mechanics, and repeated testing and torque cycling can loosen the base and render the entire antenna useless.


Locating the Problem
The easiest way to locate PIM problems within a site is to simply step through the installation using a low PIM load. The low PIM load is the most important accessory used with PIM testing. It is the reference used to ensure that PIM results are accurate. Because PIM testing is a dynamic test, it is important to manipulate each connection to try to excite any latent problems. Bending cables slightly or tapping lightly on components will easily identify PIM problems while under test. Never hit anything harder than you would knock on a door, and never over-bend a cable.
Not all PIM causes can be found so simply, however. In fact, sometimes the source of PIM is not even at the tower. That is why Anritsu developed its MW8219A PIM Master™, which can accurately and quickly locate the source of PIM, whether it is at the base station or in the surrounding environment.
A cell site constructed with PIM in mind will cost less to maintain over time. This same site will show cleaner performance than similar sites that were not PIM tested.

 

Questions and Answers

Question: If I use a very narrow resolution bandwidth compared to the span, will I miss some frequencies as the instrument sweeps?

Answer: For all detector types – except Sample – enough measurements are made for each display point that there are no gaps in frequency coverage. The Sample detector makes one measurement per display point, so gaps will occur if the resolution bandwidth is < 1/551 of the span.

Question: Why does the noise floor change when I alter the RBW or add input attenuation on my spectrum analyzer?

Answer: When you select a wider resolution bandwidth, more noise comes through the filter and causes the noise floor to rise. When you add an internal input attenuator, an instrument will increase IF gain to maintain a constant reference level. The added gain causes the noise floor to rise by an amount equal to the added attenuation.

Question: When should I use Line Sweep Tools (LST), Master Software Tools (MST) and Handheld Software Tools (HHST)?

Answer: If you routinely work with cable, antenna, or PIM traces, LST is optimized to speed up your work. If you focus on spectrum traces, transmitter test, or backhaul test, MST supports these functions. HHST is the predecessor to LST and is best used if you have an “A,” “B,” or “C” series Site Master.

 

Test Tip

You can use the Synchronizing Signal (SS) from an LTE base station and a BTS Master™ to estimate LTE coverage. It’s more convenient and less expensive than drive test systems. An application note that explains it all is available at anritsu.com.
 

Growing Field Test Concern Addressed by PIM Master

 
MW8210A
 

Expanded data services and the growing use of mobile video are causing tremendous bandwidth strain on wireless networks. Maintaining network performance under these conditions requires test solutions that can measure a number of factors. One is PIM, or passive intermodulation.
PIM is caused by items that were traditionally thought of as linear. Once they’re loaded with heavy cellular traffic, these components behave differently and can generate spurious signals that can create interference that results in dropped connections.

 
Conventional PIM testing and fault location traditionally involve an entire tower crew going to a site and basically dismantling everything with no guarantee that the source of the problem will be found. Anritsu has changed this costly scenario with the development of the MW8219A PIM Master, which can verify if receiver interference at a cell site is caused by an intermodulation product of two or more transmit frequencies. Capable of working with certain Site Master™, Spectrum Master™, Cell Master™, and BTS Master™ models, PIM Master makes it easier and more cost effective to locate PIM.
PIM Master uses Anritsu’s new patented Distance-to-PIM (DTP) technology. Developed in Anritsu’s lab, DTP eliminates uncertainty, as it can determine if the cause of PIM is from the antenna system or the surrounding environment. Another unique feature of the MW8219A is its 40 W testing, compared to alternative methods that only measure at 20 W.
 

Tough Sites Prove No Match for Anritsu Handheld Analyzers and Those that Use Them

   
A devastating tornado. Blinding blizzards in the Rocky Mountains. Being stalked by mountain lions. These are just some of the challenges cell site engineers and technicians overcome on a daily basis. The one thing they all have in common? Anritsu handheld analyzers, based upon some of the entries submitted for the Anritsu Toughest Site Contest.
Take Mike Moderski and his team of six field engineers. In less than a year, they successfully tested and installed 92 base stations, tested and swept 552 antenna systems, and ensured that 300+ T1 lines were operating properly. Thankfully, they had the MT8222A BTS Master™ every step of the way, including a site in Venice, Louisiana that is one foot below sea level, another site sitting 14,000 feet on the Rocky Mountains, as well as another in the scorching heat of Death Valley. Those weren’t the biggest challenges, though.
“We have been chased by elk, stalked by a mountain lion, had to run from bears and snakes, and swat wasps, mosquitoes, and spiders. We even had one site infested with rats. Our test equipment was dropped, kicked and bounced around vehicles and in all types of conditions,” explains Mike. “Temperature changes and rough handling didn’t affect the MT8222A. It delivered time after time!”
Maintaining multiple sites in less than ideal conditions is something Mike shares with Matthew Myers. He and his team maintain close to 40 sites that can only be accessed via a snow cat from as early as October to as late as August. Temperatures can drop as low as -50° F and winds can reach speeds as high as 110 MPH on top of the mountain. Even in these conditions, there is no margin for error.
“I’ve spent three days cutting a trail to a site. This takes time and money, so I can’t afford to make mistakes. In our job, we have to trust our vehicles, clothing, and each other because we are our own rescue team. My test gear is no exception; the results have to be accurate. I trust all my Anritsu gear,” states Matthew.
 
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Mother Nature can bring an entirely different set of challenges, as Todd Hollingsworth discovered in June of last year. A 400-foot guided tower that housed a base station and microwave radio that carried voice and 3G data was devastated by a tornado. As Todd recounted, the tower was literally ripped out of the ground and dragged across the field.
Using Anritsu Site Master™ analyzers and power meters, Todd and his crew were able to do all the path alignments and antenna sweeps to verify output quickly and efficiently, in order to get the site back on in a timely manner.
For Jeremy Dorminy, the challenge is man made. One of the sites he maintains sits on top of a peanut silo. To get there, Jeremy has to maneuver around manufacturing equipment as it’s operating, take an old ragged elevator to the roof, then climb a ladder to the site – all while carrying his test gear.
The portability of the Anritsu equipment is only one advantage, according to Jeremy. “The analyzer’s RL sweep feature allows me to find faults with lines and antennas. I can also conduct DTF to determine if I need a tower crew or if it’s something below that I can repair myself.”
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