CBNT flashcards

49 cards. Read the term and the definition here. The deck at the top of this page is optional.

HFC architecture

Hybrid fiber-coaxial network: headend or hub sends optical signals over fiber to a node, which converts them to RF for the coaxial trunk, feeder, distribution, and drop that reach the subscriber.

Fiber node function

A fiber node receives downstream optical signals, converts them to RF for the coax plant, and converts upstream RF back to optical for transmission to the hub. It defines the service group boundary.

DOCSIS 3.1 OFDM

DOCSIS 3.1 uses orthogonal frequency-division multiplexing downstream, with channels up to 192 MHz wide and modulation up to 4096-QAM, plus OFDMA upstream for greater spectral efficiency.

Amplifier cascade effect

Each RF amplifier in a cascade adds noise and distortion, reducing CNR and increasing CSO/CTB. Longer cascades therefore limit plant performance, which is why fiber-deep designs shorten them.

Compression connector rule

Coax F-connectors should be compression type, not crimp, because compression gives a more reliable, moisture-resistant mechanical and electrical bond and better shielding against ingress and leakage.

Center conductor protrusion

The coax center conductor must not extend past the connector face into the port. A protruding stinger damages the mating connector, creates impedance mismatch, and causes signal reflections and ingress.

APC versus UPC connectors

SC/APC connectors are green with an 8-degree angled end-face; SC/UPC are blue and flat. Mating APC to UPC causes high loss and back-reflection, so the two styles must never be connected.

OTDR launch cable

An OTDR launch cable is a known-length fiber jumper placed before the first connector under test. It allows the instrument to measure that first connector accurately, which it otherwise cannot resolve.

dBmV to dBm conversion

In a 75-ohm system, dBmV equals dBm plus 48.75. For example, 0 dBmV corresponds to about 48.75 dBm, allowing coax RF levels and optical power readings to be compared.

MER acceptance threshold

Modulation error ratio is measured in dB and higher is better. Common DOCSIS acceptance is at least 30 to 33 dB for 256-QAM, with DOCSIS 3.1 OFDM often requiring 33 to 35 dB or more.

Pre-FEC versus post-FEC BER

Pre-FEC bit error rate is measured before forward error correction and should be very low, such as 1E-6 or better. Post-FEC BER should be essentially zero after correction is applied.

Upstream transmit level window

The cable modem upstream transmit level should fall within the plant design window, often roughly 35 to 50 dBmV depending on tap value. Readings at the top of the window suggest loss or misalignment.

FCC leakage limit

Under 47 CFR 76.605(a)(11), cable plant leakage measured 3 meters from the plant must not exceed 20 microvolts per meter, a limit that applies especially in protected aeronautical bands.

Leakage and ingress link

Leakage and ingress occur at the same physical faults, such as cracked cable or loose connectors. Repairing the fault stops both egress interference and upstream ingress noise entering the plant.

Noise funnel diagnosis

A noise funnel is a rising upstream noise floor seen as more modems transmit. It indicates ingress from many sources or a common fault, and is observed with a spectrum analyzer at the node.

CSO and CTB distortion

Composite second order and composite triple beat are distortion products from amplifier nonlinearity. They appear as discrete beats and worsen as amplifier output levels rise above rated design values.

Drop ground block bonding

The drop ground block must be bonded to the building grounding electrode system per NEC Article 820, using copper conductor. Gas lines and unbonded water lines must never serve as grounds.

Ladder 4-to-1 rule

A ladder should be set so the base is one quarter of the working height away from the wall, giving a 4-to-1 ratio, with three points of contact and no work above the top rung.

Laser safety in fiber work

Never look into a fiber end-face or unterminated connector. Use an optical power meter to confirm no light is present before inspection, and treat all fiber as potentially live at all times.

Plant-side escalation

When measured levels show the fault is outside the drop, open a ticket with the tap identifier and level data rather than repeatedly replacing customer equipment, which does not fix plant faults.

PON splitter loss

A passive optical splitter divides one fiber among many subscribers. A 1:32 splitter introduces roughly 17 dB of loss, which must be included in the optical loss budget calculation.

Optical loss budget

Total optical loss equals fiber attenuation, about 0.35 dB per km at 1310 nm, plus splice loss, connector loss, and splitter loss. The sum must stay within the transceiver's budget.

Mid-split and high-split

Spectrum plans define upstream bandwidth: low-split uses 5 to 42 MHz, mid-split 5 to 85 MHz, and high-split 5 to 204 MHz. Higher splits increase upstream capacity but require plant upgrades.

Fusion splice loss target

Fusion splices should typically achieve 0.1 dB loss or less, while mechanical splices target 0.3 dB or less. Connector loss targets are about 0.3 dB for UPC and 0.5 dB for APC.

OTDR reflective event

On an OTDR trace, connectors appear as reflective spikes because of the air gap, while splices and bends appear as non-reflective step-downs in backscatter. This distinction helps identify fault types.

Coax tilt definition

Tilt is the difference in signal level between the lowest and highest downstream channels. Amplifiers use equalizers and slope to flatten tilt, since excessive tilt degrades high-frequency channel performance.

MER versus SNR

For QAM signals impaired only by noise, MER is approximately equal to SNR. When the impairment is nonlinear, such as clipping or CTB, MER degrades faster than SNR, revealing distortion.

Spectrum analyzer RBW setting

Resolution bandwidth should be small enough to resolve the carriers being measured, often 30 to 100 kHz for 6 MHz channels. Averaging traces reduces noise and improves readability.

Digital channel power measurement

Digital carriers have a flat, noise-like spectrum, so channel power must be measured with the meter's channel-power function rather than a peak detector, which would over-read the level.

Leakage unit conversion

Field meters often display leakage in dBmV/m, while FCC limits are stated in microvolts per meter. Convert using E in microvolts per meter equals 10 raised to the dBmV/m divided by 20, times 1000.

Laser clipping cause

Excessive upstream RF drive to the node laser pushes it beyond its linear range, causing clipping that raises MER and BER. Reducing upstream levels or adding attenuation restores linear operation.

Impulse noise detection

Impulse noise consists of short bursts from appliances, power lines, or arcing that cause uncorrectable errors without raising average MER much. BER history or impulse-noise meter functions help detect it.

NEC Article 820 grounding

NEC Article 820 covers coaxial cable grounding and bonding, requiring the drop ground block to connect to the building grounding electrode. Article 770 covers optical fiber cable installation.

Lockout tagout requirement

OSHA 29 CFR 1910.147 requires lockout and tagout of energy sources before servicing powered plant. Coax and fiber should be treated as energized until verified otherwise.

Customer documentation practice

Technicians should record signal levels before and after work, the repairs performed, and parts used, then give the customer a summary and ticket number for future reference and follow-up.

Service group capacity math

Per-subscriber bandwidth equals total service group capacity divided by active subscribers. Node splits, additional channels, and higher spectrum splits are the standard ways to increase capacity.

RG-6 versus RG-11

RG-6 is the standard coaxial drop cable for residential installations, while RG-11 has lower loss and is used for longer runs. Quad-shield RG-6 improves shielding against ingress and leakage.

CNR design target

Carrier-to-noise ratio is measured in dB and decreases with each amplifier stage. A common design target is 40 to 43 dB or better at the subscriber for digital services.

Aeronautical band leakage priority

Leaks in the protected aeronautical bands, 108 to 137 MHz and 225 to 400 MHz, are priority repairs because they can interfere with navigation and public safety communications.

Fiber inspection scope use

A fiber inspection scope magnifies the connector end-face to reveal dirt, scratches, or damage. End-faces should be cleaned with lint-free wipes and approved solvent, then re-inspected before mating.

Return loss acceptance

Return loss at the outlet should generally be at least 16 to 18 dB. Poor return loss indicates impedance mismatch caused by bad connectors, kinked cable, or unterminated ports.

Upstream node receive level

The combined upstream level at the node must stay within the receiver's dynamic range. Too high causes clipping and distortion; too low produces noise-limited BER and dropped packets.

Uncorrectable codeword monitoring

Uncorrectable codeword counts should remain at zero over a sustained test. A steady rise over time indicates ingress, laser clipping, or amplifier distortion that requires plant investigation.

PPE for field work

Field technicians should wear gloves, safety glasses, a hard hat, and safety shoes, and use a spotter near traffic. PPE requirements follow OSHA general industry and construction standards.

PON upstream multiplexing

In a PON, downstream traffic is broadcast to all ONTs on the split, while upstream traffic is time-division multiplexed so each ONT transmits in an assigned time slot.

Visual fault locator use

A visual fault locator injects visible red light into a fiber to reveal breaks, tight bends, and bad connectors by the glow of escaping light. It is a quick first-line diagnostic before OTDR testing.

Spectrum analyzer reference level

The reference level sets the top of the spectrum analyzer display. It should be adjusted so the trace stays on-screen without clipping, allowing accurate reading of signal and noise levels.

FCC leakage monitoring program

Operators must maintain a leakage monitoring program, patrol the plant, log leaks with location and level, and repair them, as required under FCC Part 76 rules for cable television systems.

TIA-568 and TIA-607

TIA-568 defines structured cabling standards for commercial buildings, and TIA-607 defines grounding and bonding requirements. Both are commonly referenced alongside NEC Articles 770 and 820.