technical training session - scte-isbe san diego...
TRANSCRIPT
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Technical Training Session
August 20th, 2014
Return Path Impairments
Presented by Bruce Smylie Arcom Digital
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Topics 1) Noise Impairments a) Noise Funneling b) Ingress vs. Impulse Noise 2) Common Path Distortion – CPD 3) Impact on performance a) CNR b) MER c) Service calls, line calls, repeat calls, overall node performance 3) Remediation a) Traditional b) Preventive
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Noise Funneling
• Simply put, noise funneling is the summation of all unwanted noise into the return path
• Includes noise generated within the subscribers home, noise generated by active devices (Gaussian noise), noise generated as a result of poor or broken shielding allowing unwanted signals to “ingress” into the cable plant, noise generated when working on plant
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Noise Funneling
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Impulse Noise
• Impulse noise is defined as “noise caused by electromagnetic interference into a cable networks characterized by pulses with a duration typically under 10 uS”. (1)
• Due to the Funnel Effect, a single Impulse Noise source can impact an entire node, sometimes causing laser clipping. Fortunately, Impulse Noise is short duration.
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Impulse Noise Impulse noise is difficult to locate due to it’s
intermittent nature much like the signals from ham radio operators and CB radios and is usually shorter duration. Typically, this type of noise comes from motors with brushes. Induction type motors are usually very quiet in nature. Brush type motors are the most common on hair dryers, vacuum cleaners, electric mixers, electric drills and other small AC power tools.
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Impulse Noise
• Some larger motors are capacitor start, induction run motors which may generate a fairly severe noise spike when starting.
• Bottom line, Impulse Noise source can be elusive and many times appears to “fix itself”.
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Impulse Noise
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Ingress Noise
• Ingress noise is defined as “noise caused by electromagnetic interference into cable networks. Its power decreases with increasing frequency. It is permanently present but slowly varying in intensity as a function of time”. (1)
• Common sources of ingress noise include CB, short wave radio, amateur radio.
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Ingress Noise
• In the return frequencies between 5 and 47 MHz, there are amateur radio frequencies in use at 7.0 to 7.3 MHz, 10.1 to 10.15 MHz, 14.0 to 14.35 MHz, 18.068 to 18.168 MHz, 21.0 to 21.45 MHz, 24.89 to 24.99 MHz, and 28.0 to 29.7
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Ingress Noise
Amateurs may operate with up to 1500 watts peak envelope power (PEP) on all these frequencies except 10.1 - 10.15 MHz, where power is limited to 200 watts PEP.
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Ingress Noise
Loose connectors or line connectors that have been improperly installed cause most of the difficulties you will encounter in the outside plant. Similarly, at the drop, you can expect problems related to F-connectors that are loose and/or corroded.
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Ingress Noise
Single-shielded drop cable can be another source of ingress. In the case of some older plant, there may be enough degradation in the drop cable to cause not only problems with the reverse path, but also for downstream digital services.
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Source of Ingress Points
• Customer Equipment
• Loose connectors
• Damaged cable
• Craftsmanship
• Improperly disconnecting customer (i.e. customer has dish or other service provider that is using existing inside wiring and signals feedback into cable network)
• Many, many more
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Ingress Noise
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Ingress Noise
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Ingress Noise Modem causing CNR alarm
Corrected by using RSA
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Ingress Noise
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Ingress and Impulse Noise
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Sources of Ingress
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Common Path Distortion
• An inter-modulation distortion created by nonlinearities found at metallic junctions.
• Downstream signals encounter a defect that is acting as a diode
• In the NTSC analog world, these distortions are observed at every 6 MHz intervals
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• Corona effect
Air ionizations, Plasma effect
• Magnetic materials
Hysteresis
Core saturation
• Poor Contacts
• Loose, corroded
• Non linear behavior
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CPD is a non-linear distortion
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CPD
• Occurs on both downstream and upstream portion of the cable network
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CPD
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CPD
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CPD
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CPD
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CPD
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Sources of CPD
Every connector interface in coaxial plant is potential source:
– Terminators
– Splitters
– Amplifiers
– Junctions
– Splices
– Taps
– Filters
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Sources of CPD
– 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
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Sources of CPD
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Sources of CPD
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Sources of CPD
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Sources of CPD
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Sources of CPD
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Sources of CPD
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Sources of CPD
• Defect causing both CPD and Ingress
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SNR Terminology
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Impact on performance
• CNR reduction caused by raised noised floor
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Impact on performance
• CNR Reduction
• MER Impact
• Slow modem traffic
• Noisy telephony
• Loss of data traffic (outage)
• Increased truck rolls
• Increase in repeat calls
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Traditional Remediation
• Traditional methods include one tech at headend talking with one tech in field as pads are pulled or power disrupted
• This is not only intrusive but many times only temporarily eliminates CPD or Ingress source
• Wait until problem is customer affecting
• Pull pad or power , breaking diode effect
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Preventative Approach
• Know the overall health of your network
• Prioritize work load by knowing which areas have what type of problem
• Minimize system downtime by utilizing non – intrusive techniques
• Utilize tools and materials that minimize subscriber induced ingress
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Overall Network Health
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Overall Network Health
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Overall Network Health
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Q&A Reference Material