On Site Testing for PIM

PIM- Passive Intermodulation

David (Dave) Bedford

Sales Manager

PIM Analysers

Agenda

Introduction: About Rosenberger Section I: PIM Basics

What is PIM? Why test for PIM? What causes PIM? PIM source examples

Section II: PIM Analyzers and Terminology How they work dBm or dBc? Receiver noise floor and residual PIM Measurement uncertainty and residual PIM

Section III: PIM Analyzer Operation Control Panel and display Set-up for test Perform test Save data and create report Remote operation

Section IV: Test Methodology Component PIM test Cable system PIM test Total system PIM test Trouble shoot

Founded 1958 Hans Rosenberger Sr.

Headquarters Germany and China

14 Manufacturing Facilities Worldwide

Worldwide Sales 345 Million USD

Founded 1958 Hans Rosenberger Sr.

Headquarters Germany and China

14 Manufacturing Facilities Worldwide

Worldwide Sales 345 Million USD

Site Portable PIM

AnalyzerCalibration/Termination

Site Solution Products

Coaxial Connectors & Adaptors

Cable and Cable Assemblies

Fiber Optic Cable Systems

Test and Measurement Products

13 yrs rack mount PIA

Now site portable PIA

Automotive Connectors

Coax JumpersFiber DistributionPower Dividers

Mounting Hardware

Coax JumpersSurge ArrestorsFiber Distribution

Main FeederCoaxial/Optical Fiber

Grounding Kits

Installation Tools

Coaxial and Fiber Optic Cables

Rosenberger Site Portable PIM Analyzer

Lab quality yet portable & rugged Simple Operation Efficient data storage and report generation Protected display visible under direct sunlight Low -168dBc (2x20W) residual PIM for accuracy Stringent test capabilities

Swept as well as 2-tone Power levels from 5 to 40Watts per test tone Meet IEC Test Standard Stress PIM sources Stay above noise floor limitations Dynamic verification with 2-tone time plot

Remote PC operation and direct graphical report Limit alarm (pass/fail) Accessories included

Low PIM load & PIM standard Three Low PIM test cables plus connector adaptors Replaceable test port connector Torque and adjustable back up wrenches Cleaning kit and other

Section I: PIM Basics

What is PIM?

Why test for PIM?

What causes PIM?

Examples

PIM Passive Intermodulation Basics Intermodulation (IM) or frequency mixing results from non-linear behavior

I

V

Linear Behavior

V

I

Non-Linear Behavior

IM generated by passive components is PIM

Transmission line systems include many metal-to-metal junctions

Metal-to-metal junctions exhibit either linear or non-linear behavior

Non-linear Loose contact with sandwiched oxides/contaminates simulate diode

Rough contacting surfaces alter electron flow at voids (tunneling)

Linear by design: highly conductive non-magnetic materials, uniform high contact pressure, smooth surface finish, low current density, durability

Non-linear in service: workmanship, faulty installation, contamination, damage, over stressed, poor solder joint, environmental effects, aging

Any connected transmission line component is a potential PIM source

External (non-connected) PIM sources can also exist if excited by EM fields

Two carriers impinging a non-linear junction generate a multitude of IM products

PIM Products from Non-Linear Junctions

IM order significance Lowest odd orderhighest powerclosest to fundamentals (potential Rx band) IM bandwidth spreads = fundamental bandwidth multiplied by IM order number Increases PIM vulnerability for advanced wide band architectures

Multi-carriers and their products further mix Manifests as noise floor risedesensitizes receivercalls droppedcapacity limited BTS and mobiles power up but IM power increases at faster rate (3dB : 1dB)

F1 F2

IM3

IM7IM5

IM9

IM3

IM5IM7

IM9

Lower IMs Upper IMs

Frequency

P

o

w

e

r

Frequencies of all IM productsFIM(O)= m(F1) n(F2)

Regulatory block pairing precludes low order IM in Rx band (>5th), but new bands under limited spectrum are jeopardizing this coordination abilityTest for IM3easiest to detect

Frequency of lower odd IM Products

FIM3= 2(F1) F2

FIM5= 3(F1) 2(F2)

FIM(O)= m(F1) n(F2)

where O = Order = m + nFor upper odd IMs interchange F1 & F2

Noise Floor Rise Desensitizes Receiver

Receiver inherent thermal noise, noise floor, limits recognition and processing of weak signals

Receiver sensitivity is minimum input signal that can be processed to produce a specified output

The required minimum signal strength above noise floor is generally expressed as S/N ratio

System performance depends on signal strength above receiver sensitivity

PIM raises the noise floor thus desensitizing the receiver

Noise

Rise

S

i

g

n

a

l

S

i

g

n

a

l

Min S/N

Min S/N

Receiver

Sensitivity

Degraded

Receiver

Sensitivity

Signal Strength

Below

SensitivityAbove

SensitivityEqual Signal Strength

Rationalize On Site PIM Testing

PIM creates interference/noise that desensitizes receiver Coverage reduces Calls drop Data rate slows Capacity reduces

Potential of high power PIM products falling in receive band is increasing Multi-band and co-located operation Higher power and carrier combining Addition of new bands under limited spectrum

Advanced architectures more vulnerable and sensitive Increased channel bandwidth Full capabilities depend on optimum noise floor

DTF, RL, and IL tests do not detect PIM Quickly and easily validate linearity of as-built infrastructure

Isolate PIM sources Corrective actions restore systems performance capabilities

Demonstrated effectiveness in finding cause for illusive service problems Degraded performance = dissatisfied customers = lost revenue

Rx Diversity Imbalance Duplex Broadband Noise Rise

Duplex

Rx Onl

y

Test Point A

Test Point B

TP BTP ATx Off

TP ATx On

RSSI Rx0: -62.6dBm

RSSI Rx1: -81.5dBmThreshold = 5dB

PIM analyzer isolated

problem to antenna

Noise rise desensitizes receiverLost revenue: service deterioration

Trouble Shooting - Simple Process of Elimination

Check PIM of easily accessible first terminate with low PIM load: OK

Replace antenna with low PIM load: PIM level still OK

Acceptable low PIM validates antenna problem or external PIM source

PIM testing antenna by itself confirmed sourcehigh PIM level

Replacing antenna restored diversity balance and service quality

Cracked Solder Joint Evidence of Corrosion

Antenna Power Divider

Other Examples of PIM Sources

Internal External

Anywhere there is loose or non-uniform metal contact and/or contamination can be PIM source

Connectors are common faultworkmanship/contamination/loose or non-uniform contact

PIM is very sensitiveworkers tools or keys can be a PIM source

During testing with antenna, workers should stand still and either be above or below antenna

PIM sources can be external if impinging radiated field intensity is sufficiently high

External PIM sources are most difficult to identify but sometimes obvious

PCS

PCS

Tx/Rx0

Rx1

Cellular Duplex

Rx0 RSSI= -64dBm Rx1 RSSI= -71dBm

B-Ba

nd C

arrie

rA-Band Carrier

Roof Top - External PIM Source Example Service Affected Rx Diversity Alarm PIM test system less antenna OK

PIM test antenna OK

Kicking vent identified PIM source

Replacing vent restored diversity balance and service quality

Rusty Roof Vent

Demonstrated service affecting examples infrastructure / external Probability for IM products falling in Rx bands increasing with time Advanced architecture more sensitive (broadband high speed digital) On site PIM tests

Reveal hidden design, workmanship, and installation flaws (RL insensitive) Promote robust quality components and installation Validate linearity to preclude unnecessary service limitations

On site PIM testing is quick and easy Site commissioning Infrastructure reuse Maintenance checks and trouble shooting

Verifying linearity can prevent illusive service degradation Customer satisfaction $$$ Maintenance $$$

Acknowledgement- Scott Semone, MTS Engineer Verizon Wireless, who cooperated in providing data and findings included in this presentation

Section I: Summary and Additional Comments

Section II: PIM Analyzers and

Terminology

How does the PIM analyzer measure PIM?

What is difference between dBm and dBc?

What is receiver noise floor and residual PIM?

How does residual PIM affect measurement accuracy?

f1

f2

DUT

Low PIM Load

Receiver

Signal Source

Tx -Filter P1

P2

P4

P3

Rx

Filter

Tx -Filter

Filter Module

System Hardware

Accessories

PA

PA

PIM Analyzer Block Diagram

Two generated signals (test tones) of different frequencies and monitored power levels (operator set within transmit band) are output to the DUT. When a non-linear junction is encountered, a multitude of resulting PIM signals propagate both in forward and reverse directions. The analyzer selects only that reflected PIM signal which is in accordance with set IM order and then displays/records its power level and frequency. In 2-tone mode there is only one PIM frequency. With sweep mode multiple frequencies are possible and will be displayed in accordance with start/stop settings.

PIM Measurement Units dBm or dBc

dBm is an absolute power level,

referenced to a mW

dBm= 10log(Watts/mW)

=10log(Watts*1000)Watts= 10x

dB= 3

dB= 10

Watts= 2x

dBc is the dB down from the test tone power

Example: Test tone power= +43dBm and IM3= -100dBm

Then dB= +43 - (-100)= 43 + 100= 143dB

A negative sign is used to designate dB below test tone; i.e. -143dBc

Industry test standard specifies 2x20W (2x43dBm)

Stresses PIM source to operational power levels

IM products do not change 1:1 with test tone power (3dB:1dB)

Provides level playing field for comparisons

Analyzer Residual PIM and Noise Floor

Analyzer residual PIM is its internal PIM level

Analyzer receiver noise floor can limit residual PIM

Before taking PIM data check residual PIM and noise floor Use test standard settings: 2 x 20W (2 x 43dBm)

Both should be

Example

PIM criterion for DUT is

Section III: PIM Analyzer Operation

Rosenberger Site Portable

Front panel controls and display

Set-up procedure

Perform PIM test

Save data and create report

Remote operation

Rosenberger Site PIM Analyzerfront panel

ModeLock keys/other buttons ineffective for this model Soft keysstep frequency (arrows)set time & day/dBm or dBc/IM order/step size/alarm limits Two channel hard keysset 2-tone F1 & F2 frequencies/power levels/start stop sweep/RF on/off Key paddata entryright bottom is enter key, any key is escape key Red LED lightsindicate RF power on Red measurement buttonsstart 2-tone single/continuousstart sweep mode single/continuous Displayshows all settings (visible even under direct sunlight) USB portssave data to memory stick and remote operation

Setting up Analyzer Turn on AC power switch15 minute warm up is recommended Use menu and soft keys to preset parameters

dBm or dBc, Date & Time, IM order, alarm limits, & step size

For 2-tone mode use hard keys to set test tones F1 & F2 frequencies and power levels

For sweep mode use hard keys to set start and stop frequencies for F1 & F2 Sweep mode test consists of two sweepsone up and one down The up sweep is F1 start to F1 stop while holding F2 at its start The down sweep is F2 start to f2 stop while holding F1 at is start Recommend leaving sweep at its default settingassures max PIM products

View set-up screen to verify all settingsif set up screen is not being displayed Hit soft esc key to return from menu or any key to return (escape) from other modes

Verify noise floor and residual PIM at test port

Set-up Screen Display - Verify Test Set-up at a Glance

Last setup before powering down, will be initial setup when powering back up

Analyzer Receiver Noise Floor Verification

AC power on but RF off (no 2-tone or sweep test):

Analyzer Residual PIM at its Test Port

AC and RF power on (2-tone or sweep test):

Functional Test at Instrument Test Port

2-tone or sweep test: Compare with PIM reference level within 2dB, 2 x 20W (2 x 43dBm)

Press 2-tone

or sweep

Compare against

PIM reference

Low PIM

Load

DIN m/m

adaptor

Caution: Avoid bumping low PIM load when connected directly to test port

Do not confuse PIM standard for DIN adaptor

PIM

Reference

Functional Test Result with -110dBm (-153dBc) PIM Reference

Analyzer Residual PIM Check at Test Port Extension

Perform 2-tone or sweep mode test: Increased residual PIM indicates deterioration of test cable affecting measurement accuracy in accordance with table in a previous slide

Verify dynamic stability of test cable

Take care of test cable, avoid excessive and frequent bending near connectors

Note/verify receiver noise floor level as described in previous slide

Perform Functional Test with PIM Reference

Perform initially and/or if data appears unrealistic

Allow 15 minute warm up

Insure connectors are clean inside and free of debrisuse canned air and/or alcohol with q-tips and swabs as necessary

Insert PIM reference between end of test cable and low PIM load

Always use torque wrench with backup when tightening connectors

If test cable has significant insertion loss, power settings should be increased accordingly

Press red 2-tone or sweep RF power button and verify PIM level is within 3dB of PIM reference (depends on cable quality and compensation for IL)

To preserve test cable PIM quality, avoid flexing/bending within 5 inches of connector Condition of test cable can impact check resultif necessary eliminate cable to isolate problem

Repeat test with PIM standard directly attached as demonstrated in earlier slides Before turning on RF power, always make sure the supplied low PIM load is used to terminate

components. Other loads may not be low PIM or capable of handling high power.

Perform PIM Test of Component or System

Identical to functional test except PIM standard is replaced by DUT

Un-terminated components must be terminated with low PIM load

Function of 2-tone or sweep buttons respectively

Single short press= single 10 sec 2-tone or single frequency sweep

Press and 2-sec hold= continuous 2-tone digital display or continuous

frequency sweeps

After test cycle completes a soft key save appears

Press any key to escape and return to setup screen

Press save soft key to save data to memory stick inserted in USB port

A prompt instructs to use key pad and enter 3-digit file name

Saved file name will be selected 3 digits prefixed by time stamp

Use PIA software to generate data report

Create Data Report- load data file

Create Data Report- select file from saved folder

Create Data Report- result with ability to reformat

Create Data Report- select add comments

Create Data Report- add comments

Create Data Report- save final results as pdf file

Create Data Report- final result

Remote Operation- set band

Remote Operation- setup test parameters

Remote Operation- adjust parameters as in manual mode

Remote Operation- press start or stop measurement

Remote Operation- save pdf

Section IV: Test Methodology

Component PIM test

Cable system PIM test

Total system PIM test

Trouble shoot

Test Methodology Ground test tower top components including antenna

Antenna ground tests require special treatment to avoid false positive Support antenna above ground away from metal objects pointing to clear sky Set antenna perpendicular to unavoidable near-by metal objects (chain link fence) Verify no interference- compare noise floor into load against into antenna

Noise floor rise with antenna connected is interference Antenna PIM test accuracy will be limited by noise floor rise

Identify possible external PIM sourceorient antenna for lowest PIM level Antenna should not be hypersensitive to realistic dynamic test

PIM test cable system PIM test complete system Trouble shoot cable system

Isolate by changing location of load and test point Be suspicious of any metal/metal junction, especially connectors Perform tap and dynamic tests monitoring stability of PIM level

Trouble shoot complete systemfails when antenna added Possible interference or external PIM source Isolate by verifying noise floorif rise then interference exists Orient antenna direction, increase elevation adjust to max up and change azimuth Re-check cable system terminating with load at last component before antenna Look for any obvious external PIM sources in near proximity of antenna If problem cannot be found in short time, log condition (Verizon Advisory)

Documents

On Site Testing for PIM