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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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Tips on Mitigating External PIM Sources

PIM

PIM interference causes LTE networks to invoke higher error protection and decrease modulation complexity, resulting in significantly lower data throughput. Proper workmanship in the preparation of coaxial cable has a very large impact on PIM performance, but it is no small chore considering that these connections are often made at the top of a tower under adverse weather conditions. The other challenge is to eliminate PIM sources in the RF path occurring beyond the antenna aperture, which has become difficult since cell sites are now deployed on rooftops, at street level, and inside buildings. While the non-linearities themselves are relatively similar, different techniques must be deployed in each environment to minimize external PIM generation.

  • Rooftop Installs – Directional panel antennas with 65° azimuth beamwidth and 5°-15° elevation beamwidth are typically deployed. The most effective way to minimize external PIM in rooftop applications is to avoid metal objects within the antenna´s half-power beamwidths by placing antennas near the edge of the rooftop with a clear view of the sector being served.

  • External PIM Sources - Reducing exposure of metallic objects within the antenna´s half-power beamwidth is a start, but may not eliminate all external PIM problems. In the near field of the antenna, radiation patterns are not fully formed. Metal objects in the near field may couple energy more strongly than if located in the antenna´s far field. Highly non-linear objects, such as metal safety chains or loosely overlapping sheet metal, should be avoided in the antenna´s near field and especially avoided within one wavelength of the antenna aperture.
  • Indoor Installs - Most indoor antennas are omni-directional with very wide elevation beamwidth due to the antenna´s small size, making it virtually impossible to avoid illuminating metal objects. While “pointing” the antenna away from PIM sources is not a viable option, re-positioning the antennas a small distance can be very effective. Movements as small as 0.5 m can reduce PIM levels significantly.
  • Street Level Installs – Small cell deployments often utilize street lamps and telephone poles to provide coverage at the street level. With an omni-directional pattern and almost no ability to re-locate the antenna away from external PIM sources, other techniques must be deployed. One solution is to use quasi-omni antennas.

 

Though each installation type has its own challenges, the proper mitigation techniques can reduce external PIM and improve site performance.

 

3 Keys: Interference Hunting

If you are looking for an easier way to locate interference sources, here are three key reasons to use the MA2700A Handheld InterferenceHunter™:
 
  • Simple – With the interference mapping feature included, an easy-to-read bar chart shows current signal levels with lines indicating maximum and minimum levels, so inexperienced users can properly aim the antenna to find the interference source.
  • Economical – One MA2700A and several antennas is 1/3 the price of a comparable solution. Plus, the MA2700A is antenna agnostic, creating additional savings that can amount to thousands of dollars.
  • Efficient – Locating sources of interfering signals via direction finding and mapping means time is saved hunting for interference.
Interference Hunter
 

Test Tip

Omnidirectional or omni antennas are convenient for making over-the-air (OTA) measurements on LTE networks. Modulation quality specifications for LTE transmitters are 8% EVM or less at 64 QAM. This limit should be used when making a direct connect measurement, with the addition of a small factor for instrument contribution. For OTA measurements, a larger factor should be added to consider the signal path. As a general rule, readings under 10% are acceptable. Many modern transmitter designs, however, are much better than this; OTA readings from an ideal location can also be much better than this. A good approach is to take an OTA measurement when the base station is commissioned to establish a benchmark to maintain going forward.
 

Enhanced Distance-to-PIM Leads to More Accurate PIM Analysis

An enhanced Distance-to-PIM (DTP) technology in the PIM Master™ MW82119A improves resolution by a factor of two to make it easier to locate and eliminate PIM sources more quickly in the field. With enhanced resolution, easy-to-read red bars clearly mark the locations of PIM sources on the analyzer display. DTP quickly and accurately identifies the location of PIM faults inside the feed system as well as beyond the antenna to eliminate the guesswork involved in isolating PIM sources. A new trace overlay feature allows real-time comparison between the active DTP measurement and a previously saved DTP trace to compare “before and after” results on a site or to clearly show the distance between an unknown PIM source and a “PIM marker” placed in the system. Other enhancements include two new Trace Modes to optimize PIM vs. time measurements. FAST Trace Mode supports dynamic PIM testing, where maximum responsiveness is desired. LOW NOISE Trace Mode improves accuracy in low-signal level measurements. 
 

Cell Master Survives the Rigors of Seven Years on the Road

Like most site technicians, Ken R. must endure the elements on a daily basis. Some days, it is sweltering heat, other times it is sub-zero temperatures. Driving rainstorms can come during any season, and then there are the hail storms for which the Midwest is famous. There is another environmental challenge that all site technicians can relate to, as well. “Over seven years, my Cell Master™ has been thrown around and survived the ups and downs of bouncing in the back of my truck. I’ve dropped it from at least ten feet up more than once. Despite all of this, I have never had to send it in for any repairs,” explains Ken. Ken maintains numerous sites throughout Kansas and Missouri. He uses his Cell Master almost every day to test the performance of dual band 850/1900 active antennas, tower mounted amplifiers (TMAs), and RF radiating coaxial cabling and jumpers. The Cell Master is invaluable when he measures Bias-T adapters to verify return loss/VSWR, cable loss, and distance-to-fault (DTF). “I have come to rely on my Anritsu Cell Master to get me through the toughest situations. When I am in extremely harsh conditions I know I can rely on the Cell Master to locate faults that cause equipment VSWR alarms,” said Ken. “It is invaluable when performing traditional line sweeps and traces to verify return loss/VSWR and DTF measurements, and checking Tx power levels.” For Ken, the reliability and durability of the Cell Master makes it his handheld test solution of choice. Despite its compact size and light weight, the Cell Master is designed with a highly durable housing that meets MIL-PRF- 28800F Class 2 requirements for shock and vibration, and the analyzer has a wide operating temperature range of –10 ºC to 55 ºC. “I could not perform my every day job duties without this test set. The instrument’s reliability and simplicity make my life easier in the field,” said Ken. No ability to re-locate the antenna away from external PIM sources, other techniques must be deployed. One solution is to use quasi-omni antennas. 
 
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