Technical Training Session

August 20th, 2014

Return Path Impairments

Presented by Bruce Smylie Arcom Digital

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

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

Noise Funneling

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.

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.

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”.

Impulse Noise

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.

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

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.

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.

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.

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

Ingress Noise

Ingress Noise

Ingress Noise Modem causing CNR alarm

Corrected by using RSA

Ingress Noise

Ingress and Impulse Noise

Sources of Ingress

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

• Corona effect

Air ionizations, Plasma effect

• Magnetic materials

Hysteresis

Core saturation

• Poor Contacts

• Loose, corroded

• Non linear behavior

CPD is a non-linear distortion

CPD

• Occurs on both downstream and upstream portion of the cable network

CPD

CPD

CPD

CPD

CPD

Sources of CPD

Every connector interface in coaxial plant is potential source:

– Terminators

– Splitters

– Amplifiers

– Junctions

– Splices

– Taps

– Filters

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

Sources of CPD

Sources of CPD

Sources of CPD

Sources of CPD

Sources of CPD

Sources of CPD

Sources of CPD

• Defect causing both CPD and Ingress

SNR Terminology

Impact on performance

• CNR reduction caused by raised noised floor

Impact on performance

• CNR Reduction

• MER Impact

• Slow modem traffic

• Noisy telephony

• Loss of data traffic (outage)

• Increased truck rolls

• Increase in repeat calls

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

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

Overall Network Health

Overall Network Health

Overall Network Health

Q&A Reference Material