pim training

8/10/2019 PIM Training

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Passive Intermodulation PIM)


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Passive Intermodulation Fundamentals

John Miller

Applications Engineer

Kaelus(office) +44 (0)1383 437920

(mobile) +44 (0)7800 542843


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AMERICAS: EMEA: APAC:

Global Technical Service & Support


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What is Passive InterModulation (PIM)

PIM = Interference

PIM = Noise generated by Tx signals interacting with

materials in the RF path.

PIM = Reduced BTS Coverage and Capacity.


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The result

MANY unwanted frequencies are generated.

f1

f2

f1+f

2f

2-f

1

2f1-f

2

2f12f

2

2f2-f

1

3f2-2f

14f

2-3f

1

3f1-2f

2

4f1-3f

2

Interference

Interference

Desired


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PIM order

Frequency

Amplitude

f1

f2

f1+f

2f

2-f

1

2f1-1f2

2f1

2f2

2f2-1f1

3f2-2f14f

2-3f

1

3f1-2f24f

1-3f

2

3rdOrder

5thOrder

7thOrder

The order of an intermodulation product m*f1n*f2 = m+n.

2*f1-1*f2 = 3rd order product

4*f2-3*f1 = 7th order product.

The lower the order the higher the level (typically)

Odd products are most likely to fall in the Rx band.


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PIM is getting more complex with

Networks evolution towards:

Indoor or outdoor complex DAS

systems (shared by several

operators)

Site sharing with multiple transmit

carriers (same RF infrastructure for

multiple operators)

Multi-technology sites (GSM 900

MHz, GSM 1800 MHz, UMTS 2100

and 900 MHz, CDMA 450, ...LTE)

Combining Unit

GSM 900GSM 1800WCDMA

OP1

BTS

OP2

BTS

OP3

BTS

OP1

BTS

OP2

BTS

OP3

BTS

OP1

NodeB

OP2

NodeB

OP3

NodeB

Load

1800/W

CDMA

900/

1800

Triplexer

RF Output ports

PSPS

PSPS

PSPS

PSPS

Outdoor

area

AntAnt

AntAnt

AntAnt

PSPS

AntAnt

AntAnt

Ant

PSPS

PSPS

AntAnt

PSPS

AntAnt

AntAnt

AntAnt

PSPSAntAnt

PSPSAntAnt

PSPSAntAnt

PSPS

AntAnt

Indoor

Area 1

Indoor

Area 2

Indoor

Area 3

Indoor

Area 4

Indoor

Area 5


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What are the main PIM Sources

Non-linear metal-to-metal contacts:

Loose RF connectors.

Poorly prepared RF cable terminations

Improperly mated / misaligned parts

Cracked / cold solder joints

Loose mechanical fasteners (screws,

rivets)


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Incident signals

Reflected signals

Ideal Infrastructure

Transmitted signals

Minimum loss

Minimum

Reflections measured by sweep test

Measures the quality of impedancematching in the system.

Linear Infrastructure

(No new frequencies)


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Incident signals

Reflected + interference signals

Transmitted signals

Non-ideal Infrastructure

Reflections still measured by sweep test

Interference measured by PIM tester

Non-Linear Infrastructure

(Creates new frequencies)


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Possible to have Same Band intermodulation

issues

3rdorder

5thorder

7thorder

GSM900

935 MHz 960 MHz890 MHz 915 MHz

900 GSM Rx band 900 GSM Tx Band

935 MHz 960 MHz890 MHz 915 MHz

900 GSM Rx band 900 GSM Tx Band

GSM1800

1805MHz 1880MHz1710MHz 1785MHz

1800GSM Rx band 1800GSM Tx Band


1800GSM Rx band 1800GSM Tx Band

UMTS2100


2100 UMTS Rx band 2100 UMTSTx Band


2100 UMTS Rx band 2100 UMTSTx Band


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Also, Cross Band intermodulation issues

involving UMTS

DCS1800 into UMTS2100

1805MHz 1880MHz 1920MHz 1980MHz

1800GSM Tx band UMTS2100 Rx Band

3rdorder

5thorder

And with LTE there are multiple combinations nowadays


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Where to look for PIM on statistics?

Main search focus on:

GeneralCDR, CSR, CSSR

GSM

GSM Mean interference on Idle (IOI)

TCH Completion Rate and Drop % TRAFFIC RATE Erlangs

TCH Assignment Rate

SDCCH Assignment rate and drops

HO Success Rate

UL Quality Erlang Minutes Per Drop

DROP_AFTER_TCH_ASSIGN

SDCCH_RADIO_FAIL

CDR data and voice

RRC Success rate% RAB Establishment Success %

Voice Traffic Erl

PS Traffic (Mb)

Average Throughput

RTWP RSSI

UMTS


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PIM Source

PI

M

PI

M

TX 1

TX 2

TX 1 TX 1

TX 2

TX 2

PIM Test Equipment

PI

M Low PIM Load

How does a portable PIM tester work?


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-100 dBm

0dBm

0dBc

-143 dBc

=

dBm dBc

Power relative to the carrier levelAbsolute power relative to1mW

PIM level is expressed in either dBm or dBc

CARRIE

R

PI

M

2 x 20 Watts

CARRIER

+43 dBm

PI

M


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PIM level is meaningless without also stating

the carrier power level.

PIM level is VERY dependent on test

power level.

~3dB change in PIM level for every 1dB

change in test power.

2W not enough power to certify a site.

IEC 62037 recommends 2x 20W

(+43dBm) test carriers.

-100 dBm

CARRIER

PIM

+43 dBm

20 Watts

0dBm

CARRIER

PIM

2 Watts

-130 dBm

+33 dBm

Noise Floor


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PIM test process at cell site:


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Site

Guy Wires

Steel Tower

Other Sites IMD

RF In-Line Surge Arrestors

Low Grade Antennas

Roof Flashing/Vent Hoods

Installation

Poorly torqued connectors

Scratches

Stress Fractures

Contamination

On conduction materials

Dielectric material

Materials

Rust

Ferromagnetic materials

Poor Quality Plating

Test Equipment

Poor Quality Loads

Low quality or damaged

jumpers, adapters and

connectors

Misc.

Cracked / Cold Solder joints

Contact Pressure

PIM Sources at the cell site:


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Resistive loads

generate PIM


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90 connectors

typically not as

good as straightconnectors.


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RF Connector Selection:

Avoid using Type-N

7-16 DIN connectors are more robust and produce less PIM


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Poor cable

preparation

Dirt / trash


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Poor cable

preparation


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Poor cable

preparation


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Cabledamage


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PIM testing should be dynamic

Passing a static PIM test does not necessarily insure long termperformance.

Lightly tap RF connections.

Flex cables while holding connector fixed.

If PIM level jumps out of specificationmake repairs.

Find problems before Mother Nature does!

Wind induced vibration

Temperature variations


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Dynamic versus Static testing:

Fault locations are found by gently tapping on connections or components

Tapping on a bad junction causes PIM to spike

Dynamic PIM testing is very important!

Finds the location of static PIM failures

Stresses all connections to make sure that the feed system is robust and will

not fail prematurely due to environmental exposure (Hot, Cold, wind loading,

vibration, etc.)


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PIM

Incident signalsTransmitted signals

Reflected + interference signals

Linear Infrastructure

PIM sources can be external to the system!


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External PIM Sources


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Typical 65 Beamwidth Antenna Patterns

4 ft. (1.2m) 800MHz

8 ft. (2.4m) 800MHzEnd View

(Azimuth Pattern)Side View

(Elevation Pattern)


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If external PIM is suspected, rotate antenna on

mast.

PIM PIM

45 Rotation


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Elevation tilting may be more effective to

identify external PIM sources.

PIM PIM

15 Rotation


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Antenna Testing

Make sure there are no PIM sources within

the field of view of the antenna!

Recommendations:

BE SAFE!

Point antenna toward the sky.

No metal objects within the half-power

beamwidths of the antenna in both

Azimuth and Elevation.

Antenna should be placed on non-metallic

supports during test.

Test equipment and test operators should

be located off the end of the antenna; not

the side. Use a known good antenna to verify the

test environment before testing.

PIMPIM

PIM

SKY

SKY


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Testing Antennas

Empty

cardboard

boxes

(NO STAPLES)

Large PVC

pipe


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PIM Tests

S


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Summary

PIM = reduces site performance

PIM sources can be eliminated / minimized through:

Careful construction techniques

Use of low PIM components. Careful site design.

PIM testing should be dynamic (not static)

PIM testingANDVSWR testing are needed to verify systemperformance.


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KAELUS field trial evaluation

PIM S i EMEA b KAE US


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KAELUS trials:

>319 feeder lines surveyed.

26 Operators and OEMs, 17

countries

Many PIM problems recorded

Few VSWR problems found

The sites were originally

commissioned with Sweep test

equipment so it is no surprise thatthe VSWR results are good

PIM Survey in EMEA by KAELUS

70.37%

3.09%

29.63%

Sites or sectors with PIM

problems

Sites or sectors with

VSWR problems

Sites or sectors without

PIM Problems


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PIM S i EMEA b KAELUS


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The PIM defects found wereprimarily due to workmanship

issues at the RF connections.

Many lines had multiple

defects

KPI impro vements repor ted

on the major i ty of si tes that

PIM was detected and

repaired at site

PIM Survey in EMEA by KAELUS

65.35%

28.95%

13.60% 14.04%

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

Connectors Jumper Cables Other Passive Antennas


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GSM 900 Greenfield Site



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GSM 900This site has suffered repeated intermittent ULQUAL issues and been visited many

times.

On the 22/10 with the riggers changed the antenna because of bad PIM measurements.

PIM detection and Correction



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GSM 900 + WCDMA 850 Indoor DAS System

GSM 900 WCDMA 8 0 I d DAS


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GSM 900 + WCDMA 850 Indoor DAS

A carrier operating a WCDMA850 network overlaid on a GSM900

network had an in-building distributed antenna system suffering fromhigh Dropped Call Rates (DCR).

The DCR was logged over a period of time and plotted in. There was a

significant increase when the CDMA equipment at the site was

switched on.

GSM 900 WCDMA 850 I d DAS


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After all PIM generating connections were reworked the receiver noise floor was

reduced to -112dBm.

Rx Noise

floor before

PIM testingRx Noise floor

after

reconstruction

using PIM

tester

Here -a 5dB gain

at the noise floor

GSM 900 + WCDMA 850 Indoor DAS


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UMTS2100 Rooftop Site


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3G Rooftop

Urban dense site

Surge Arrestors were the source of PIM

After their replacement

Drops in Voice and Packet improved


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p p

After PIM changes

PIM t t i t iQA S i


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PIM test equipment: iQA Series

High Power Premium

Adjustable power (2

20W) Adjustable frequencies

Rugged construction

Integrated transit case

Panel PC with touch screen interface,

on-board reporting

Accessory Kit:


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Accessory Kit:

Transit case

Jumper cables

Adapters

Wrench Torque Wrench

Low PIM load

PIM source

Cleaning kit


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iQA Series


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Precautions

iQA Ph i l Ch t i ti


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iQA Physical Characteristics

3 Stage folding tow handle

Wheels

Fold away bench

mounting legs

Shock mounted

electronics

360air inlet filter

surrounding electronics

Rugged protective case with

three external lifting handles

Cooling Fans

One each side

4 internal


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iQA

Software

OPERATOR TEST SCREEN


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Test Point Label

Numeric Level

indication: Displays

RF OFF - Rx Noise

Floor

RF ON - PIM

Function ButtonsLevel 2 access

indicator/lock

HPA temperature

indication

F1 & F2 test

carrier power levels

Alarm StatusIM3,5,7 or 9 frequency,

by selection

F1 & F2 test

Frequencies

RF test power ON/OFF

button

PIM level Bar indicator

Active with RF on

Adjustable Pass / Fail

threshold indicator

OPERATOR TEST SCREEN

ALARM SCREEN


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ALARM SCREEN

Touching here toggles between the

operator and alarm screen

Touching any Red indicator will

provide a short description of

the fault and any action that

should be attempted by the

operator in this space

These green

icons will turn

red to indicated

a fault

Test Set Operator Security Levels


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Test Set Operator Security Levels

.Level 1Set State UserLevel 1limits the operator to operating

with preset test states (preset frequency,

test power, test time, pass/fail threshold

and test point labels).

Level 2Open User

Level 2allows the operator access to all

configuration and test facilities supported

by the instrument.

Access to the test set alarm status and the report screen is available to both levels.

Level 1 touch controls


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toggle between dBm and dBcswitch to Report screen

record test result while test

power is on

select report label for the next

test sequence

turns audible PIM level buzzer

on and off.

used to load test states from

USB drive.

Provides Level 2 access

Initiate soft shutdown of the test

set.

switches to the Alarm status

screen

switches Test Power (RF) On and

Off

Accessing Level 2


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Accessing Level 2

Step 1. Touch this button to

bring up Password keyboard..

Note: Factory default password is left blanktouch enter only before

user password has been set.

Level 2 Menu


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Level 2 MenuLevel 2 access indicator/lock shows as unlocked.

A touch on this open icon will relock the access to this level

Resets all variable to those set during manufacture

Closes the iQA application and returns user to the MS

Windows Desktop

Returns to the test function buttons leaving all level 2 touch

controls available to the operator

Allows setting of Test period via the pop up key pad shownAllows setting of Test period via the pop up key pad shown

Level 2 Test Point Labels


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Level 2 Test Point Labels

Allows configuration of test point labels via the secondary

screen shown below

Allows setting up and editing of test point labels.

Refer to the User Manual for additional information as

necessary

Returns to test screen

Level 2 Test states


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Level 2 Test states

Returns to test screen

Allows access to, saving and renaming test states.

Level 2 Password


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Level 2 Password

Allows setting and changing of Level 2 access password.

Level 2 touchcontrols


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locks out level 2 access

Set pass/fail test threshold

Set F1 test power

set F1 set F2 Selects IM3, IM5, IM7,

IM9 or IM11

Set F2 test power

Note: Level 2 users have access to all Level 1 controls


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Testing examples

and Q&A

Our PIM test ing heri tage :


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g g

Developed factory PIM test systems for RF

Equipment manufacturers in 1996.

>800 FactoryPIM test systems in service

Developed Portable PIM systems for

wireless operators in 2004.

>1800 PortablePIM test systems in service


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2 l ll h d

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