on site testing for pim
TRANSCRIPT
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On Site Testing for PIM
PIM- Passive Intermodulation
Christian Entsfellner
Productmanager
Rosenberger Germany
Laddie Basa
Technical Sales Engineer
Rosenberger Site Solutions
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On Site Testing for PIM
PIM- Passive Intermodulation
David (Dave) Bedford
Sales Manager
PIM Analysers
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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
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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
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Coax JumpersFiber DistributionPower Dividers
Mounting Hardware
Coax JumpersSurge ArrestorsFiber Distribution
Main FeederCoaxial/Optical Fiber
Grounding Kits
Installation Tools
Coaxial and Fiber Optic Cables
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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
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Section I: PIM Basics
What is PIM?
Why test for PIM?
What causes PIM?
Examples
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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?
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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.
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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
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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
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Example
PIM criterion for DUT is
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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
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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
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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
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Set-up Screen Display - Verify Test Set-up at a Glance
Last setup before powering down, will be initial setup when powering back up
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Analyzer Receiver Noise Floor Verification
AC power on but RF off (no 2-tone or sweep test):
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Analyzer Residual PIM at its Test Port
AC and RF power on (2-tone or sweep test):
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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
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Functional Test Result with -110dBm (-153dBc) PIM Reference
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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
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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.
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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
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Create Data Report- load data file
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Create Data Report- select file from saved folder
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Create Data Report- result with ability to reformat
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Create Data Report- select add comments
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Create Data Report- add comments
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Create Data Report- save final results as pdf file
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Create Data Report- final result
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Remote Operation- set band
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Remote Operation- setup test parameters
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Remote Operation- adjust parameters as in manual mode
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Remote Operation- press start or stop measurement
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Remote Operation- save pdf
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Section IV: Test Methodology
Component PIM test
Cable system PIM test
Total system PIM test
Trouble shoot
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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)