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CPD Troubleshooting

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The pin of the terminator was corroded and loose. ... The impairment was found in 4 stops after the node and fixed within an hour and a half. ... – PowerPoint PPT presentation

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Title: CPD Troubleshooting


1
CPD Troubleshooting
2
The CPD Problem
  • Most frustrating, time-consuming network issue to
    troubleshoot
  • Comes and goes unpredictably
  • Disappears when you think youve found it
  • Reappears after the problem has been fixed
  • No cable service provider is immune

3
Why treat CPD?
  • CPD greatly diminishes network performance and
    reliability
  • Services with higher modulation formats are
    easily distorted by CPD
  • digital video
  • High-speed Internet
  • Digital phone services

4
What is CPD?
  • An intermodulation distortion of downstream
    signals due to nonlinearities found at metallic
    junctions.

5
The Common Path
6
Where is CPD Found?
  • Every connector interfaces in coaxial plant is
    potential source
  • Terminators
  • Splitters
  • Amplifiers
  • Junctions
  • Splices
  • Taps
  • Filters

7
Physics of CPD
  • Contaminated interfaces oxidation
  • Bimetallic Corrosion - Electrochemical corrosion
    between dissimilar metals
  • Single Metal Corrosion - Corrosion from air and
    moisture in unprotected metals
  • Crevice Corrosion - Connectors
  • Stress Corrosion - Stress corrosion at bend,
    shear, and clamp points
  • Temperature, vibration, humidity
  • Lubricants, cleaning solvents, skin oils
  • Diode Effect

8
Causes of CPD Loose Connections
  • At microscopic level, contacts are comprised of
    many contact surfaces separated by cavities
  • Surface area and pressure govern conductivity
    characteristics
  • As connectors age, adequate contact surface area
    and pressure may be lost, creating CPD
  • Insertion/installation may create stress points
    that are catalysts for corrosion formation
    leading to CPD

9
Nonlinear Intermodulation Diode Effect
  • Nonlinear - A signal that passes through a device
    and the shape of the signal from the input to the
    output is changed.
  • Beats
  • F1 - F2
  • F1 F2

Channel Beat
Channel Beat
Channel 7 175.25 MHz Channel 8 181.25
MHz Channel 9 187.25 MHz Channel 10 193.25
MHz Channel 11 199.25 MHz Channel 12 205.25
MHz Channel 13 211.25 MHz
8 minus 7 6 MHz 9 minus 7
12 MHz 10 minus 7 18 MHz 11
minus 7 24 MHz 12 minus 7 30
MHz 13 minus 7 36 MHz
8 plus 7 356.50 MHz 9 plus
7 362.50 MHz 10 plus 7
368.50 MHz 11 plus 7 374.50 MHz
12 plus 7 380.50 MHz 13 plus 7
386.50 MHz
10
Return path without CPD
Signs of CPD
  • 6 MHz spikes in return path 6, 12, 18, 24 MHz
    ..
  • Raised return path noise floor
  • Elevated CSO/CTB in the downstream

Return path with CPD
11
Why treat CPD? - cont
  • Non-linear Intermodulation
  • Ingress
  • Impedance mismatch / suck outs
  • BER/MER
  • Reflections

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Severity, Unpredictability and Prevention
  • Degree of corrosion in the formation of a diode
  • Distance of corroded connector and forward output
    of an amplifier
  • Magnitude of the forward and reverse signals at
    the CPD source
  • Day-Night Effect and Temperature
  • Vibrations
  • Clean connectors
  • Dry connectors
  • Proper connection

29
Conventional CPD Remediation
  • Wait until the problem is severe
  • Use two or more techs
  • One to monitor spectrum analyzer
  • One or more techs in the field to disconnect
    devices until problem is isolated
  • Labor intensive and disruptive
  • Unreliable with no positive confirmation of fix

30
Conventional CPD Remediation
  • Last amp in
  • First amp out
  • Halves
  • From known feeder leg termination back to amp
  • Contractors to change out equipment

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Go Interactive
45
Procedures and Results
46
Background
  • The following are results from the first week of
    the live trial performed from 12/3/07 through
    12/7/07.
  • Network troubleshooting using Hunter was
    performed 12/4 12/6.
  • Two teams of technicians with Arcom
    representatives worked in 10 of the 32 designated
    trial nodes fixing 13 impairments using Hunter.
  • The trial effectively demonstrated that CPD
    sources could be easily identified and
    permanently repaired.
  • The following is a description of the work that
    was performed, procedures taken and ending
    results.

47
Node WI137 step 1
  • This node presented a CPD source located at
    120.525uS from the headend server. Once
    determining to work on this this node, the first
    step was to go to the node and isolate which leg
    the source of the impairment is located.

48
Node WI137 step 2
  • Using the Quiver handheld radar, we measured CPD
    9.15uS from the node coming from the west leg.
    After inputting the time-distance into Quiver
    Navigator maps, Navigator directed us to the next
    logical split at amp AM0022.

49
Node WI137 step 3
  • Now at amp AM0022 we used the Quiver handheld
    radar again and without taking the network down
    we were able to measure a CPD time-distance at
    4.87uS coming from the western leg. After
    inputting this time-distance into Navigator we
    determined to proceed to amp AM0034.

50
Node WI137 step 4
  • At amp AM0034 we used the Quiver probe on the
    seizure screw test point of splitter SP0012 and
    measured CPD 2.4uS heading north. Quiver
    Navigator showed the source of the impairment to
    be located at tap TP0197 or terminator TM0026.

51
Node WI137 step 5
  • At the tap TP0197 and terminator TM0026 location,
    technicians went through their normal
    troubleshooting of visually inspecting the
    equipment, tightening connections and replaced
    line terminator TM0026. The pin of the
    terminator was corroded and loose. Using headend
    mode in the Quiver we verified that the CPD
    impairment was fixed.
  • We were able to locate and fix the source of this
    nodes impairment within 50 minutes and in 3
    determined stops after the node.

52
CPD Stats for WI137
  • The graph below represents the CPD statistics for
    Node WI137 from 12-4-07 through 12-7-07. This
    nodes impairment was in high alarm from 12pm to
    11pm on 12-4-07. Even though this impairments
    amplitude dropped to a low level on 12-5-07, we
    were able to track and fix during normal work
    hours using Hunter.

9.15uS repair
53
Node WI122
  • This node had 3 impairments fixed over the first
    week of the trial. On 12/4/07 there was CPD at
    4.15uS from the node. In 3 stops we found and
    fixed a cracked cable at the input connector at
    the tap. On 12/6/07 there was CPD 8.4uS and
    10.89uS from the node. Both impairments were
    tracked to line terminators and were fixed within
    1 hour.

54
Node WI122 Graph 12/4 12/7
4.15uS repair
8.4uS repair
10.89uS repair
55
Node VC003
  • Using Quiver at the node we measured CPD 13.78uS
    (approx 6063 feet from node). By knowing the
    time-distance and using our Quiver Navigator maps
    we were able to bypass 5 amplifiers, 6 splitters
    and 4 DCs. The impairment was found in 4 stops
    after the node and fixed within an hour and a
    half. Source was a line terminator.

56
Node BA001
  • BA001 showed 2 sources of CPD at 2.62uS and
    10.8uS from the node. We were able to track both
    concurrently down the same leg. Sources split
    off of different legs out of amp AM0031. After
    fixing the closer impairment we went back to
    AM0031 and proceeded to track and fix the farther
    impairment. Both sources were line terminators.

2.62uS repair
10.8uS repair
New intermittent CPD source
57
Node WI042
  • We measured CPD 4.60uS from the node. In 2 stops
    from the node we located a cracked cable wrapped
    in aluminum foil and tie wraps. I new piece of
    cable was spliced in and fixed the impairment.

58
Node WI043
  • Measured CPD 5.64uS from node. In 4 stops we
    tracked source to a terminated tap with a broken
    port and 2 blackened terminators

59
Node WI093
  • Distance to the CPD source from the node was
    3.87uS. In two stops after the node source of
    impairment was a bad terminator on a DC-7

60
Node WI048
  • CPD source measured at 9.505uS from node.

Node BA006
  • CPD source was measured 7.575uS from node.

61
Before/After CPD Statistics
  • CPD Alarms 12-4
  • CPD Alarms 12-7

62
Before/After CPD Charts
  • Nodes with CPD 12/04/07
  • Nodes with CPD 12/07/07

63
References
Bharat Patels - Report on Common Path
Distortions http//www.arcomdigital.com/files/CPD_
report.pdf Ronald Mesavage Common Path
Distortion Communication Technology June 1,
2006 http//www.cable360.net/ct/data/15091.html
www.arcomdigital.com
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