8/16/2016 PIM Troubleshooting using Dist-to-Fault Module 1

Troubleshooting PIM Flowcharts and Practical Cases

PIM Troubleshooting is case dependent and different techniques work best in different situations. An engineer/technician using Common Sense, Experience and understanding of how to use the tools/measurements available are generally the best means to resolve PIM issues in the most efficient and effective manner. This PPT suggests a flowchart to follow which highlights the importance of using all the PIM tester measurements available before declaring a PIM issue resolved.

The author generally performs a system level PIM test initially by using a BTS (or CW) source to drive a DAS system and generate its own PIM products. Then identify which REMOTES are causing the PIM at a system level. Follow flowchart once remotes are identified with PIM.

Shane Spiteri – RF Engineer

PIM TROUBLESHOOTING FLOWCHART

• For efficiency - PIM identification can start with a system level check. i.e. Use REMOTES to generate PIM,

• Identify which REMOTES are causing PIM and then proceed to START of flowchart,

• Ensure that STATIC, DYNAMIC and SWEPT PIM is used to ensure REMOTE is passing PIM (See following slides to show case-studies),

• Use best combination of Common Sense, Experience and Dist-2-PIM module to help locate PIM sources and remedy,

Static PIM Check

Dynamic PIM Check

Swept PIM Check

NO PIM DETECTED(Passive Section has Passed PIM Check

PIM Source Identifiable (Braided Cable, Bad Connector?)

Isolate Passive Paths to determine PIM Source

PASS

PASS

Perform PIM Mitigation

PASS

Distance-to-PIM available?

start

WHY PERFORM DYNAMIC TESTING?

• Initial STATIC PIM testing shows no PIM exists from this HiPower REMOTE,

• DYNAMIC testing was performed on the connector to reveal High PIM,

• Note: Often PIM sources can be generated between the HiPower BTS and the DAS POI, e.g. Loose connector on LTE700. Perform Dynamic Testing in HeadEnd.

Tapping on cable revealed PIM Issue from bad connection. Rule of thumb: 1inch motion at length 1ft

Dynamic testing using Tap Test. Move high power cable 1inch side-to-side about 12inch back from connector and Tap on Connectors.

Figure 1 - Uplink Spectrum measured using Spectrum Analyzer, sniffing off from UL monitoring port of RRU or RU. STATIC TEST SHOWS NO PIM is detected at this time.

Figure 2 - Uplink Spectrum measured using Spectrum Analyzer, sniffing off from UL monitoring port of RRU or RU. DYNAMIC TEST SHOWS HIGH PIM LEVELS.

TAPTAP

WHY USE SWEPT PIM?

• DAS-to-PIM PASS or Static/Dynamic PIM Test does not guarantee a PIM Pass. Swept PIM is useful to ensure system is PIM-free, especially for a wideband signal.

Figure below shows a Dist-to-PIM result with peak of -147dBc at 78ft. The figure to the right shows a Standard Test reading of -153.4dBc at 1870Mhz. If the pass criteria was -150dBc, one could consider this system as PIM-free based on this measurement.

However, this system is not PIM free. Use of Swept-PIM function shows that over the 1900Mhz Uplink band, the PIM results vary. The figure on the right shows a reading of -139.2dBc at 1900Mhz.

Figure 1 – Dist-to-PIM reading for a system measured. -147dBc at 78ft.

Figure 2 – Timed PIM reading of -153.4dBc at 1870Mhz.

Figure 3 – Swept PIM across the 1900Mhz UL Band. Shows varying PIM levels by as much as 15dBc

Figure 4 –Timed PIM reading of -139.2dBc at 1900Mhz .

Determine which hardline contains source of PIM

Splitter at 90ft

RU1

RU2

RU3

RU4

• After testing each Hardline from the Remote Closet using the Dist2PIM (DTF module), one of the hardlines showed high PIM levels,

• High PIM was detected at approximately 90ft from the Remote closet,

• Using the As-Built design (Upper picture) it shows a 2nd stage splitter with Jumpers/connections that could be likely source of PIM,

Suspected Jumpers replaced at 90ft PIM source location

Old Jumpers were suspected of being PIM source due to quality of connector and age of jumper in general.

• Scissor lift was deployed to suspected location of PIM source,

• All Jumpers between hardline and splitters (MIMO) were replaced with PIM rated jumpers,

*Knowing location of PIM source reduces time & Labor costs compared with blindly changing all components unnecessarily.

Jumpers suspected at 200ft since NEW antenna

2. Now DTF module reads PIM source at 200ft.This corresponds one of the antenna locations.

1. PIM source at 90ft no longer an issue,

• Initial PIM source at 90ft is now reduced to acceptable levels after jumper replacement,

• Next highest PIM source not meeting acceptable levels is at 200ft which corresponds to one of the antenna locations,

Similarly, jumpers replaced at 200ft PIM source location

Old Jumpers between Antenna and hardline were replaced as they were suspected of being the PIM source due to quality of connector and age of jumper in general.

• Again, Scissor lift was deployed to suspected location of PIM source at 200ft,

• All Jumpers between hardline and Antenna were replaced with PIM rated jumpers,

PIM is now reduced from -85dBc to < -160dBc

Conclusions

• Use Common Sense when troubleshooting PIM:• Experience and Observation can often reveal PIM sources initially,• Is termination of every Antenna necessary? Can we isolate the passive branches?

• Ensure correct measurement techniques used to identify and remedy PIM issues,

• Along with As-Built Diagrams, DTF Module can help to identify PIM source locations more accurately,

• Knowing PIM source location can greatly improve the efficiency of PIM issue resolution,

• Reduce Time in finding PIM source,• Reduce Cost to deploy Equipment, Machinery and Labor,• Reduce Cost by not changing components unnecessarily,• Minimize rework by ensuring PIM issue has been resolved correctly,

• Whilst DTF can improve PIM troubleshooting, the benefits may not be realized in systems with less complexity and/or have components that are easily accessible,