1. Best Practices for Achieving Low PIM Performance in DAS Networks
Slide 1

2. Agenda What is Passive Intermodulation (PIM)
Sources of PIM in a DAS environment
Reasons why PIM is particularly problematic in DAS
How a PIM tester works
Best practices for mitigating PIM
Anritsu MW82119A product features

3. Passive Intermodulation (PIM)
TX Signals at site
Passive Intermodulation (PIM)
Passive Intermodulation (PIM) F1 F2
2*F1–1*F2
2*F2–1*F1
3*F1–2*F2
3*F2–2*F1
4*F1–3*F2
4*F2–3*F1
5*F1–4*F2
5*F2–4*F1
IM 9
IM 7
IM 5
IM 3
IM 3
IM 5
IM 7
IM 9
PIM = interference
PIM = new frequencies generated by TX Signals at a cell site when they encounter non-linear junctions or materials in the RF path
PIM falling in an operator’s uplink can elevate the noise floor:
▪ Dropped calls ▪ Access failures ▪ Slower data rates

4. What does PIM look like at the site?
Mobile uplink signal

5. What does PIM look like to the operator?
PIM Repair
High average noise level
BUSY
QUIET
BUSY
QUIET
Lower average noise level

6. What is a non-linear junction?
Linear junctions
Current
Voltage
Current increases linearly with applied voltage
High pressure, metal-to-metal contacts
Welded or soldered connections
Current
Voltage
Non-linear junctions
Current does not increase linearly with voltage.
Low pressure, metal-to-metal contacts
Oxide layers on metal surfaces
Arcing across small air gaps or cracks

7. What is non-linear in a DAS?
Damaged / poorly made components
Broken cracked solder joints
Loose internal fasteners
Braided cables with crimp connectors
Nickel plating
Shipping damage

8. What is non-linear in a DAS?
Out
BTS #1 Input
High power RF terminations
BTS #2 Input
Out
Notorious for poor PIM
Impact depends on frequencies being combined

9. What is non-linear in a DAS?
Metal flakes inside RF connectors
Worse when touching inner or outer conductor

10. What is non-linear a DAS?
Poor cable termination
Loose metal flakes
Rough / irregular metal edges

11. What is non-linear a DAS?
Metal flakes inside cables
Plenum rated cables have no foam to prevent metal flakes from falling inside

12. What is non-linear in a DAS?
Loose RF connectors
Must be torqued with a torque wrench

13. What is non-linear in a DAS?
Type-N connectors
Easy to damage contacting surfaces if over torqued
Tend to loosen over time
7/16 DIN connectors better
4.1/9.5 or 4.3/10 “mini DIN” connectors also better

14. What is non-linear in a DAS?
External PIM Sources
Antennas flush mounted to ceiling
Fire suppression pipes
Air handling ductwork
Metal hangers
Lighting fixtures
Ceiling tile frames
Etc., etc., etc.

15. And… there are many opportunities for PIM!
Radio 1
Radio 2
Floor 3
Floor 2
Floor 1
In this simple example:
63 RF connections
31 cable assemblies
15 antennas
14 power dividers
1 hybrid combiner
1 RF termination

16. Where does PIM occur? F1 F2
IM 3
IM 5
IM 7
IM 9
2*F2–1*F1
3*F2–2*F1
4*F2–3*F1
5*F2–4*F1
2*F1–1*F2
3*F1–2*F2
4*F1–3*F2
5*F1–4*F2
BTS Uplink
BTS Downlink
PIM occurs at mathematical combinations of the Tx frequencies
F1 = 1930 MHz F2 = 1945 MHz
IM3 = (2*1930) – (1*1945) = MHz IM3 = (2*1945) – (1*1930) = MHz
IM5 = (3*1930) – (2*1945) = MHz IM5 = (3*1945) – (2*1930) = MHz
IM7 = (4*1930) – (3*1945) = MHz IM7 = (4*1945) – (3*1930) = MHz
IM9 = (5*1930) – (4*1945) = MHz IM9 = (5*1945) – (4*1930) = MHz

17. Where does PIM occur? (the easy way)F1 F2
IM 3
IM 5
IM 7
IM 9
15 MHz
BTS Uplink
BTS Downlink

18. Where does PIM occur? (the easy way)F1 F2
IM 3
IM 5
30 MHz
BTS Uplink
BTS Downlink
Wide frequency spacing moves IM products farther apart
Increases probability that low order IM product will fall in uplink band

19. Neutral Host Systems Increase Probability that IM Products Will Fall in Rx Band
Single PCS operator:
FCC did a good job!
IM 11 first product that falls in A-block uplink
Multiple operators / bands:
Different story!
IM 3 falls in E / F block uplink
IM 5 falls in A-block

20. What is the bandwidth of PIM signals?
200 KHz
600 KHz
1 MHz
1.4 MHz
1.8 MHz
BTS Uplink
BTS Downlink
PIM bandwidth increases as carrier bandwidth increases
PIM bandwidth increase with PIM order

21. Can one wide band carrier generate PIM?
5 MHz
5 MHz
5 MHz
5 MHz
5 MHz
5 MHz
5 MHz
5 MHz
5 MHz
IM 3
IM 5
IM 7
IM 9
BTS Uplink
BTS Downlink
YES !
Signal is composed of individual sub-carrier frequencies

22. What is the solution?
LTE
GSM
UMTS
CDMA
Eliminate non-linearity so that multiple frequencies can peacefully co-exist!

23. How do we measure linearity?
F1, F2
Test lead
Load
IM products
PIM
PIM tester
PIM
With a PIM tester!
Inject two CW test signals at a known magnitude
Measure 3rd order intermodulation product (IM3)
IM3 “characterizes” the linearity of the system
If IM3 is low = linearity is good
If IM3 is high = linearity is poor

24. Reducing IM3 Reduces all IM ProductsF1 F2
IM 3
IM 5
IM 7
IM 9
IM 11
BTS Uplink (Rx)
BTS Downlink (Tx)
Noise Floor
Low IM3 = good linearity
Low IM3 drives higher order products below the noise floor

25. Best Practices for Achieving Low PIM performance in a DAS

26. 1) Start with high quality components
Only use RF components that:
Are designed for low PIM performance
Proper material selection
No loose metal-to-metal junctions
IEC provides more extensive list of design guidelines
From companies that:
Own PIM test equipment
Have their manufacturing processes under control
100% test to verify performance (-150dBc with 2x 20W test tones )

27. 2) Use crews that are PIM certified
Understand the importance of cleanliness
Use alcohol swabs to clean mated pairs of connectors
Vacuum end of cables before attaching connectors
Understand the importance of proper cable preparation
Cut plenum rated cables with razor blade cutter (not saw)
Use sharp cutting tools
Use the correct tools for the type of cable in use
Understand the importance of tight connections
Always use a torque wrench (DIN)
Do not over/under tighten (Type-N)
Have experience operating PIM test equipment

28. 3) PIM test as you build Radio 1 Radio 2
Antenna location tests Branch test Floor test
Sector test System test
Radio 2

29. 3) PIM test as you build (con’t)
Problems are identified and corrected before being replicated throughout the DAS
Faster to locate PIM sources when testing smaller sections
Easier access to antennas / splitters to troubleshoot and correct problems
Tools, materials, man-lifts, still on hand
Reduced re-work at antenna locations (when antenna locations are pre- tested)

30. Antenna Location Testing
Place antenna as close to design location as possible using low PIM pole
Perform PIM test
Low test power ( dBm typical)
Lowest frequency only (700 or 850 MHz)
Pass/Fail limit (depends on test power)
Find passing location within 1 m of design location
Small movements = big changes in PIM!
PIM tester

31. Things to Avoid Around Antennas:
For every rule there is an exception
This is why it is important to test!
Try to avoid placing antennas within 1m of:
Metal seams (ductwork, etc.)
Concrete with obvious signs of rust
Lighting fixtures
Electronic devices
Products containing RF ID tags

32. PIM Master MW82119A Features

33. Key Specifications / Capabilities for DAS
Parameter
Specification
Small size
350 x 314 x 152mm
(13.8 x 12.4 x 6.0in)
Light weight
9 kg to 12 kg *
(20 lb to 27 lb)
Battery operation
> 3.0 hours
Wide power range
25dBm to 46dBm
(0.3W to 39.8W)
Low residual PIM
-117 2x 43dBm
Distance-to-PIM™
YES
PIM vs. Time
Remote Control
* - Weight varies by frequency option

34. Battery Operation = Enhanced Portability

35. Tapping on RF connections
PIM vs. Time Capability
PIM magnitude vs. time
Tap on all RF connections while performing the PIM test
Visual indication of PIM stability
Peak PIM held for Pass/Fail
Tapping on RF connections
Limit Line

36. Distance-to-PIM (DTP) Capability
The fastest way to locate PIM
PIM magnitude vs. distance
Eliminates guess-work
Able to see PIM beyond antenna
6 markers + marker table to identify multiple sources

37. Wide Range of Test Accessories
R - Backpack Accessory Kit
R – Transit case (Holds MW82119A only)
R – Transit case (Holds MW82119A plus accessories) (accessories not included)
R - Hard Case Accessory Kit

38. Conclusion PIM is a challenge in DAS environments
Many potential sources
More harmful frequency combinations
Best practices for mitigating PIM include:
Using high quality components
Using trained installation crews
PIM testing as you build (starting with antenna locations)
Anritsu PIM Master is well suited for PIM testing in a DAS environments
Exceptional portability
Fully integrated, Distance-to-PIM (DTP) technology