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Passive Intermodulation Passive Intermodulation

FundamentalsFundamentals

V.6_4.13

Kaelus Passive Intermodulation Kaelus Passive Intermodulation Kaelus Passive Intermodulation Kaelus Passive Intermodulation Kaelus Passive Intermodulation Kaelus Passive Intermodulation Kaelus Passive Intermodulation Kaelus Passive Intermodulation Seminar/WorkshopSeminar/WorkshopSeminar/WorkshopSeminar/WorkshopSeminar/WorkshopSeminar/WorkshopSeminar/WorkshopSeminar/Workshop

Course Objectives

In this course, we will cover the following items: Introduce Passive Intermodulation (PIM) Identify sources of PIM Recognise the benefits from eliminating PIM problems Demonstrate products used for PIM testing Demonstrate through hands-on exercises:

How PIM test equipment operates Identify critical safety elements associated with PIM testing Conduct equipment verification Conduct a test Interpret PIM Results Review key elements

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Key Terms DTF Distance to Fault (Return Loss/VSWR) DTP Distance to PIM (Passive Intermodulation) RTF Range to Fault (DTF and DTP combined) DUT Device Under Test IM Intermodulation PIM Passive InterModulation RL Return Loss TMA Tower Mounted Amplifier Dynamic test Test with movement (Tap and Flex) dBm Power ratio relative to 1mW dBc PIM power referenced to Carrier power BTS Base Transmitting Station or Base station

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About Kaelus Kaelus designs and manufactures a wide range of innovative RF and

microwave solutions for the wireless telecommunications sector Within Smiths Group we rebranded as Kaelus, four existing Smiths trading

entities into a single operating unit in 2010, while preserving the technology and management of our individual companies

Kaelus experience and understanding of the radio environment enables us to excel by developing technically differentiated offerings that improve network performance

Kaelus is an operating unit of Smiths Interconnect Microwave, within Smiths Group, plc.

PIM Test InstrumentsRF Conditioning Products Site Services

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Global Support and calibration facilities

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AMERICAS: EMEA: APAC:

What is Passive Intermodulation (PIM)? PIMPIMPIMPIM = Interference

PIMPIMPIMPIM = Noise generated by TX signals at a cell site interacting with non-linear characteristics of the RF path

f1 f2

f1+f2f2-f1

2f1-f2

2f1 2f2

2f2-f13f2-2f1

4f2-3f13f1-2f2

4f1-3f2

PIMPIM

Tx frequencies

Multiple frequencies + High power + Non-linear characteristics = PIM

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What Do You Mean By Non-Linear?

Current does not increase Linearlynot increase Linearlynot increase Linearlynot increase Linearly as the applied voltage is increased Metal-to-metal contacts with low contact pressure Oxides on metal surfaces initially impeded current flow As voltage increases current begins to flow through voids and thin spots Arcing may occur across micro air gaps (cracks, surface roughness, loose

connections)

voltage

curr

en

t

These non-linear junctions behave like diodes the key component of a mixer.

Linear

Non-Linear

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Non-Linear Junctions & MaterialsMetalMetalMetalMetal----totototo----metal contacts:metal contacts:metal contacts:metal contacts: Loose RF connectors Poorly prepared RF cable terminations Improperly mated / misaligned parts Cracked / cold solder joints Metal chips / shavings inside connectors Loose mechanical fasteners (screws, rivets) Overlapping sheets of metal (flashing, vents) Loose bolts and brackets

Materials:Materials:Materials:Materials: Nickel plating on RF conductors Rust Poor or deteriorating plating on components

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PIM Sources Poorly constructed or damaged RF

components Poor Installation Improperly torqued connectors Scratches Stress fractures Contamination on conduction materials Dielectric material Site environment Guy wires Steel tower Other sites IMD Roof flashing/vent hoods Rust

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RF Connector Selection

Type N connectors will work, but 7-16 DIN connectors are more robust and are less likely to produce unacceptable levels of PIM

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6

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90connectors:Do not twist connector on cable

Sources of PIM

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Resistive loads

generate PIM

Sources of PIM

7

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Poor cable preparation:

Improper tool use

Dirt / Trash:

Cleaning

Sources of PIM

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Poor cable preparation:

wrong tool

Sources of PIM

8

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Poor cable preparation:

wrong tool

Sources of PIM

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Cable damage:

Improper tool use

Sources of PIM

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PIM trial in Europe pre 2009

>280 feeder lines surveyed. 24 Operators and OEMs, 15 countries Many PIM problems recorded Few VSWR problems found The sites were originally commissioned with Sweep test equipment so

it is no surprise that the VSWR results are good

----17171717----

70.77%

3.52%

29.23%

Sites or sectors with PIMproblems

Sites or sectors withVSWR problems

Sites or sectors withoutPIM Problems

PIM trial in Europe pre 2009 technologies

----18181818----

47

37

27 25

5 5 3 2

GS

M90

0/G

SM

1800

/UM

TS

2100

GS

M90

0

GS

M18

00

GS

M90

0/U

MT

S21

00

UM

TS

2100

GS

M90

0/G

SM

1800

GS

M18

00/U

MT

S21

00

CD

MA

450

10

PIM trial in Europe pre 2009 PIM Defects Found

The PIM defects found were primarily due to workmanshipissues at the RF connections

Many lines had multiple defects

Other passive devices with PIM problems included:

Diplexing filters

Surge protectors

Bias-Ts

KPI improvements reported on the majority of sites repaired

Survey Results

41.25%

17% 16.25%

62.50%

0%

10%

20%

30%

40%

50%

60%

70%

Feed Cables JumperCables

Antennas OtherPassiveDevices

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PIM Test Specifications

First edition of IEC 62037 was published on 9/16/1999 (>12 years ago!) Purpose: To establish a standard test method for measuring

PIM Provide a method to compare the PIM performance of different

devices Key recommendations of the specification:

1. Third Order IM products typically represent the worst case condition of unwanted signals; therefore measuring IM3 characterizes the DUT

2. PIM comparisons should be done at the same power level. (2x 20 W recommended for mobile communications systems)

3. Devices should be subjected to an impact or movement while PIM testing

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PIM Level is expressed in dBm or dBc

-100dBm

0dBm

Reference

0dBc

Reference

-143dBc=

dBm dBc

Power relative to the carrier levelAbsolute power relative to 1mW

CA

RR

IER

PIM

2 x 20 Watts

CA

RR

IER

+43dBm

PIM

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You Need to Know the Power Level

PIM level is VERY dependent on test power level

2.2dB to 3dB change in PIM level for every 1dB change in test power

As the test power changes, the measured PIM level changes

Calculating equivalent test levels when changing test power requires careful attention!

*All calculations in dBm

-100dBm

CA

RR

IER

PIM

+43dBm

20 Watts

0dBm

Reference

CA

RR

IER

4 Watts

-121dBm

+36dBm

PIM

-21dBm(3 X 7)

-7dBm

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Exercise Calculating dBcAssume that you measure two different jumper cables. The field terminated jumper is tested with the Kaelus iHA 4-watt (36dBm)

test unit and the factory terminated jumper was tested with the Kaelus iQAunit at 20-watts (43dBm). The test results are as follows:

PIM of field terminated jumper = -111dBm at 2 x 36dBm carrier power PIM of factory terminated jumper = -111dBm at 2 x 43dBm carrier power

Calculate the PIM of both devices in dBc Field terminated jumper = _________ dBc at 2 x 36dBm Factory terminated jumper = _________dBc at 2 x 43dBm

Note that both had the same PIM measurement value, -111dBm, if you ignored the carrier power. However, you now know that the test power used can give you very different results. Which is the better cable?

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Why Do We Care?

PIMPIMPIMPIM = Reduced coverage, reduced capacity and slower data rates

PIM that falls in the Rx band elevates the noise floor Reduces the ability of the system to detect real signals The primary cause of PIM is poor construction quality

Tx bandRx band

Interference f1 f2

IM 3IM 5

IM 7

IM 3IM 5

IM 7

1710

1785

1805

1880

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Also occur across band

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DCS1800 into UMTS2100

1805MHz 1880MHz 1920MHz 1980MHz

1800GSM Tx band UMTS2100 Rx Band

3rd order

5th order

And with LTE there are multiple combinations nowadays

Why Is PIM So Important Now? Dramatic increase in smart phone traffic

Higher data rates Broadband technologies Greater traffic density Video bandwidth demand

Zoning / tower loading forcing co-location Site sharing multiple operators on the same site Infrastructure sharing multiple bands and

technologies combined on the same RF path The probability of PIM falling in an operators The probability of PIM falling in an operators The probability of PIM falling in an operators The probability of PIM falling in an operators

Rx band is increasing.Rx band is increasing.Rx band is increasing.Rx band is increasing. Operators have limited spectrum and must Operators have limited spectrum and must Operators have limited spectrum and must Operators have limited spectrum and must

reduce PIM interference from stealing network reduce PIM interference from stealing network reduce PIM interference from stealing network reduce PIM interference from stealing network capacity.capacity.capacity.capacity.

Tx/Rx 900Tx/Rx 1800

Tx/Rx 900Tx/Rx 1800

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PIM is getting more complex

Networks are evolving:

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)

----27272727----

Combining UnitGSM 900GSM 1800WCDMA

OP

1B

TS

OP

2B

TS

OP

3B

TS

OP

1B

TS

OP

2B

TS

OP

3B

TS

OP

1N

od

e B

OP

2N

od

e B

OP

3N

od

e B

Lo

ad

1800/WC

DM

A

900/1800

Triplexer

RF Output ports

PSPS

PSPS

PSPS

PSPSOutdoor

area

AntAnt

AntAnt

AntAnt

PSPS

AntAnt

AntAnt

Ant

PSPS

PSPS

AntAnt

PSPS

AntAnt

AntAnt

AntAnt

PSPSAntAnt

PSPSAntAnt

PSPSAntAnt

PSPS

AntAnt

IndoorArea 1

IndoorArea 2

IndoorArea 3

IndoorArea 4

IndoorArea 5

PIM Impact On Network Performance

PIM = interferencePIM = interferencePIM = interferencePIM = interference Dropped calls Call initiation failure Reduced data rates Blocked calls Premature handoff Reduced coverage Reduced capacity

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High DroppedHigh DroppedHigh DroppedHigh DroppedCall RateCall RateCall RateCall Rate PIM induced

noise shrinks the effective cell size

Gaps in coverage result in higher dropped call rate

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Significant increase in call drops after a new carrier was added to a DAS system with PIM problems.

PIM Impact On Network Performance

High average receive signal strength indication (RSSI) differential between main and diversity paths.

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Diversity

Main

PIM problems

corrected

Rx levels

tracking

together

BTS PIM causing elevated

average noise on the Main

branch

Diversity path not impacted

Key indicator of an

internal interference

problem

External interference

would impact both paths

equally

PIM Impact On Network Performance

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GSM: Elevated Interference on Idle (IOI) channels

High interference

levels before fixing

PIM problems.

Decreased interference

after fixing PIM

problems.

Increased successful

traffic channel (TCH)

allocations

PIM problems

corrected

PIM Impact On Network Performance

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PIM problems

corrected Significant

improvement

after fixing PIM.

BTS is blind to new mobiles trying to access

the cell

Not impacting Dropped Call Rate because the

call never initiated on the sector

PIM Impact On Network Performance

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The BenefitThe Benefit

RX Noise floor RX Noise floor

before PIM before PIM

testingtesting

55dB reduction in dB reduction in

RX Noise floor RX Noise floor

after correcting after correcting

PIM problems.PIM problems.

PIM Impact On Network Performance

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Ideal Infrastructure

Input signals

Reflected signals

Transmitted signals

Minimum loss

Minimum

Linear Infrastructure

(No new frequencies)

Reflections measured by sweep test

Measures the quality of impedance

matching in the system

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Non-Ideal Infrastructure

Input signals

Reflected + interference signals

Transmitted signals

Reflections still measured by sweep test

Interference measured by PIM tester

Non-Linear infrastructure

(Creates new frequencies)

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But It Passes The Sweep Test? Yes but PIM testing and sweep testing

are very different tests

Sweep gear transmits a single frequencysingle frequencysingle frequencysingle frequency at low powerlow powerlow powerlow power (1mW) into the system and measures the magnitude of the reflectedreflectedreflectedreflectedpower at that frequency

PIM testing transmits two frequenciestwo frequenciestwo frequenciestwo frequencies at high powerhigh powerhigh powerhigh power (20W each) into the system and measures the power of the interferenceinterferenceinterferenceinterferencegenerated at a third frequencythird frequencythird frequencythird frequency

BothBothBothBoth tests are important and necessary to tests are important and necessary to tests are important and necessary to tests are important and necessary to ensure quality site constructionensure quality site constructionensure quality site constructionensure quality site construction

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But It Passes The Sweep Test? Range to Fault PIM sweep showing multiple PIM sources Note Return Loss is all OK, better than 28dB

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But It Passes The Sweep Test? Same feeder after re-terminating jumper cable at 4 meters Note: Second PIM source located at 41-42 meters after Note: Return Loss is all OK, better than 28dB

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How Does PIM Test Equipment Work?

PIM test equipment transmits 2 2 2 2 test tonestest tonestest tonestest tones at high powerhigh powerhigh powerhigh power into the system under test in order to excite any non-linear junctions

The test equipment is tuned to accurately measure and display the magnitude of the PIM generated

A typical IM3 system level field specification with 2 x 20W test tones: -140dBc (-97dBm) new construction -130dBc (-87dBm) existing sites

PIMSource

20 W

PIM Test Equipment

20 W

IM 3

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PIM Testing is Not New!

Summitek Instruments (now Kaelus) has been producing bench top PIM test systems for 15 years

Kaelus Bench PIM Analyzers are used by nearly every RF equipment manufacturer worldwide in both engineering and manufacturing

Kaelus has delivered more than 1,200 BPIM systems worldwide

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Rugged, Portable Versions

Portable PIM test sets were developed in Australia at the request of Telstra by Summiteks sister division, then known as Triasx

Kaelus has delivered more than Qty 5,000 x PPIM systems worldwide

These systems are being used by network operators worldwide to reduce PIM in their RF infrastructure

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iQA Passive Intermodulation Analyzer

High Power Adjustable power +33dBm to +43dBm Fully adjustable frequencies Full reporting functionality Rugged construction Integrated transit case Panel PC with touch screen interface, on-

board reporting Designed and developed in 2007, 3000+

units deployed globally

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8

9 10 11 12

13

15 16 14

17

18

19

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PIM test equipment: iQA Series:

Time Trace

Spectrum Analyzer

Frequency Sweep

iQA Passive Intermodulation Analyzeradditional user modes

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Range to Fault Mode (optional)

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Requires RTF enabled iQA or iPA test instrument and RTF Module

One Tx frequency is held fixed Second Tx frequency is swept across a range

of Tx frequencies Resulting PIM frequency measured that fall in

the RX band Frequency data is post-processed to create

time domain data Location of PIM faults are calculated and

displayed. Similar process occurs to calculate distance

to RL

What's New : RTF and Battery Operated Test Sets

----46464646----

Designed and built for purpose starting

with a clean sheet of paper:

Battery Powered, Light weight,

Remote Controllable, Rugged,

Durable, Reliable and compact.

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Highly portable and ruggedized design built for purpose for top-of-tower testing

Includes tablet for remote control allowing the operator at the top of the tower to have hands-free for dynamic testing and safety

IEC Specified Test Power: 2 x 20 watts Battery powered On board, touch screen interface

available for local control when necessary

Includes the Kaelus industry leading report generator

iPA Passive Intermodulation Analyzer

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iPA Key advantages

Variable output power provides versatility: In-Building, rooftop, top and bottom of tower +20 dBm to +43 dBm

Residual PIM at 2 x 43 dBm carrier power -117 dBm (-160 dBc, maximum) - 125 dBm (-168 dBc, typical)

Ruggedized and Lightweight 26 pounds (12 kg) Impact resistant display

Optional range to fault function Remotely controllable

Provides convenience in all test situations Adds to personnel safety for top-of-tower testing

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iPAConfigurable and Ruggedized for Field Testing

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Designed with tower climbers in mind

Lifting lugs at either end for hoisting and multiple hanging and mounting orientations

Rotating handles for any orientation

Webbing straps on both sides for comfortable hand carrying

iPA Wireless Remote Control

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Any device with Wi-Fi and a web browser can connect and view or control the iPA

Tablet included with the every unit Multiple devices can view data while testing as

viewers or master controllers Safety Master Control functionality avoiding

inadvertent RF transmission Top of tower control from base allowing for field

engineer at the base to control testing with tower climber making the tower top connections and dynamically testing

View multiple screens on the remote device, e.g. time trace and standard PIM.

iPA acts as an access point providing a secure wireless network utilizing WPA/WPA2 security

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1. Fill in the site details: Name the site Use ALL for sector &

feeder Enter your name as operator

2. Test parameters will be listed automatically by the software to verify the instrument settings are correct

3. Required test points: PIM source Low PIM load Port 1 (of mini BTS) Port 2 (of mini BTS) Add more as needed during

troubleshooting process

Kaelus Reports

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How do we test for PIM, Safety Review

PIM test equipment is capable of producing up to 50W of RF power in the 700 to 2600 MHz region

Users must take proper precautions to minimize exposure to RF fields: Always terminate the output port of the test equipment into a load, a loaded

line, or a line that will radiate the energy to free space before turning on the RF power

Always turn off the RF power whenever a test is not being conducted Always turn off the RF power before disconnecting a RF connection on a

line under test Burns to fingers and permanent damage to eyes can result from exposure to

connectors carrying high levels of RF power Ensure that any antenna being tested is placed so that no personnel are

exposed to RF field levels in excess of the maximum allowable exposure limits

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How do we test for PIM?

----53535353----

Perform a static PIM test first.

If the line fails terminate the line and use RTF analysis to quickly identify the location of static

PIM faults.

PIM problems are typically at RF connections!

Use the RL + PIM overlay screen to visualize RF connector locations

Fix the largest PIM fault & repeat.

Once all static PIM faults are corrected, perform dynamic PIM testing.

If the line fails while dynamic PIM testing you know where the fault is! (It is where you are

tapping!)

Is Dynamic Testing Really Necessary?

YES!!YES!!YES!!YES!! Tapping or gently flexing a faulty connection will cause the PIM to spike If the PIM goes above the specification, the connection needs to be repaired Dynamic testing makes sure that the feed system is robust and will not fail

prematurely due to environmental extremes (Hot, Cold, wind, vibration, etc.) Dynamic PIM testing is requiredis requiredis requiredis required by the IEC specification as well as your

customers. (Also referred to as Percussion Test).

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PIM Teams

PIM testing is a team activity. In order to correctly test PIM and isolate problems there is almost always going to be more than one person involved, the norm is: The person doing the dynamic testing (tap, flex of

cables, connectors, antennas, etc) May be required to climb

The person operating the test equipment

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Reduce System Down-time

PIM testing is OUT OF SERVICE testing which means it will Line Sweep test and interrupt service

There are a few steps necessary to ensure the outage is minimal or conducted at a time when traffic is low on the system: Make sure the proper NOC or operation center knows

what is about to happen (Get a clearance if necessary) Schedule the test during the maintenance window if

needed Prepare your equipment and plan (Tailgate) in advance to

minimize the outage time Notify others when the test is complete and service is

restored

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Test Frequencies PGSM 900

----57575757----

Test Frequencies GSM1800

----58585858----

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Test Frequencies UMTS2100

----59595959----

Typical Cell Site Objectives

----60606060----

Configuration3rd Order IM with 2x 20W

(+43dBm) Test Power

New construction -140dBc (-97dBm) Max Specified by US operators

New construction -150dBc (-107dBm) Max Possible new specified by US Operators for LTE networks

Existing site modifications -130dBc (-87dBm) Max Specified by US Operators

Site specifications need to be determined by the operator

Typical specification could be:

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RTF Overview

----61616161----

User Interface

----62626262----

RTF analysis mode - Overlay view

Displays overlay of PIM vs. distance and RL vs. distance graphs

Markers will be available for both RL and PIM to display the relative distance between peaks.

Errors that impact RTF accuracy impact both the RL measurement and the PIM measurement equally.

The relative distance between a known reflection (such as the end of the transmission line) and a PIM source will be more accurate than either individual RTF

measurement.

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Range to Fault Mode

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PIM RTF Graph

Return Loss DTF Graph

PIMRTF & Return Loss DTF Graph

Basic RTF Screen

PIM Sources Can Be External

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Input signals

Transmitted signals

Reflected + external PIM signals

Linear infrastructure

PIM

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External PIM

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Range to Fault PIM sweep showing PIM sources: approximately 7 meters in front of the antenna, jumper cable Approximately 3 meters in front of the antenna

Note Return Loss is all OK, better 28dBm

Antenna

External PIM

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Picture of the site showing a support approximately 3.5 meters infrontof the antenna a possible cause of PIM

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External PIM

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Elevation Tilting May Be Effective To Identify External PIM

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PIMPIM

15Rotation

35

External PIM Sources

System failed PIM testing (-120dBc)

Eliminated PIM sources inside shelter

Attached PIM load to jumper at antenna

Passed PIM (

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Antenna Testing Prior to InstallationMake sure there are no PIM sourcesMake sure there are no PIM sourcesMake sure there are no PIM sourcesMake sure there are no PIM sourceswithin the field of view of the antenna!within the field of view of the antenna!within the field of view of the antenna!within the field of view of the antenna!

Recommendations: BE SAFE! Point antenna toward the sky No metal objects within 20 of the

side of the antenna or 10 from the ends

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

PIMPIM

PIM

SKY

SKY

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Antenna Testing

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~3m

~6m

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Summary Passive Intermodulation (PIM) interference degrades site

performance

PIM testing and VSWR testing are both required to verify site performance and installation quality

Properly designed and constructed sites will have low PIM Use low PIM components Take your time and do it right the first time

Use the right tools and follow manufacturers instructions when building cables

Use a torque wrench on all connections Clean, clean, clean

Passing a dynamic PIM test certifies high quality RF system construction

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Accessories

iPA System includes: iPA-xxxx PIM Unit iPad Mini (WiFi Only) Soft bag storage Charger 1 re-chargable lithium

batteries SD Card containing

manuals

RTF Module (optional)

74

iPA Premium Accessory Kit

(iKA-0060A) includes:

Hard case

Dual charging cradle

2 spare batteries

Low PIM load

PIM Source

Torque wrench

Adjustable wrench

3-meter test cable

Adapter Kit

Cleaning Kit

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Operational Demo Review of the operator interface Creating report headers Creating test point labels Test setup verification

Measure and record low PIM Load Measure and record PIM source

Demonstrate dynamic test of cable as a system test PIM load not properly tightened Record PIM vs. time Save data Capture screen

Show other test modes Swept Frequency measurement Spectrum Analyzer mode

Measure PIM source with RF off and RF on

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PIM Testing Hands On

PIM test modes Equipment set-up Equipment verification Power levels Low PIM loads Conducting the test Trouble shooting

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