Progression: Maintenance Tech I - II Conventional
The six-step troubleshooting process
1.Identifying the problem 2.Analyzing the Situation 3.Isolating the Elements 4.Diagnosing the Symptoms 5.Resolving the Problem 6.Verifying the Solution
If the leakage detector indicates there is a leak and displays a reading of 14 microvolts per meter (uV/m) measured at 80 feet from a possible leak source, what is the approximate calculated level of the leak from 10 feet?
112 uV/m.
Across 6 MHz, what is the maximum in-channel frequency response (ICFR) defined in the Data Over Cable Service Interface Specification (DOCSIS)?
3.0 dB peak-to-valley (P/V).
Cumulative Leakage Index (CLI)
A calculation of the relative amount of signal leakage in a broadband cable network that is provided annually as a numerical score to the Federal Communications Commission (FCC) that represents a cable system's signal leakage prevention.
What is a desirable characteristic of a ferroresonant network power supply?
A desirable characteristic of a ferroresonant network power supply is a steady output voltage over a wide range of input voltages.
Long-term evolution (LTE)
A fourth generation (4G) wireless broadband technology based on Internet protocol (IP) enabling Internet access via cellular devices at potential data rates that exceed 100 Mbps downstream and 30 Mbps upstream.
Where is a standby network power supply likely to be located?
A large standby network power supply cabinet can only be mounted on a pole or set and anchored onto a concrete pad.
What could cause low-frequency roll-off of the downstream spectrum discovered when sweeping an amplifier?
A loose seizure screw in the downstream path.
Microvolts per meter (µV/m)
A measurement of a signal leak's power or intensity as gauged over a certain distance; abbreviated µV/m.
Quadrature amplitude modulation (QAM)
A modulation technique for transporting digital information using a combination of amplitude modulation (AM) and phase modulation (PM).
Monopole
A one-quarter wavelength or five-eighths wavelength vertically polarized antenna mounted on a vehicle for system monitoring; often a vehicle-mounted whip antenna used in detecting signal leakage.
Bridger amplifier
A portion of the downstream signal is boosted before being split and routed to as many as four separate coaxial cables—the branches in the architecture.
Describe the ports of a typical power inserter.
A power inserter has three ports: one port for alternating current (AC) voltage from the power supply and two ports for the combined AC voltage and RF signals
What is spliced into the hardline coaxial cable to combine the AC power with the transported RF signal in a hybrid fiber/coax (HFC) network?
A power inserter.
Why is a digital multimeter (DMM) that takes a true root mean square (RMS) measurement of alternating current (AC) more accurate when measuring the quasi-square wave output of a ferroresonant power supply?
A true RMS DMM takes several measurement samples during a wave cycle and uses complex formulas to display an accurate measurement of the quasi-square wave output of a ferroresonant power supply
What happens if a utility power outage shuts off a network power supply that sends alternating current (AC) to several amplifiers?
A utility power outage that shuts off a network power supply that sends (AC) to several amplifiers causes a service interruption to all customers served by those amplifiers.
How is alternating current (AC) inserted into the network through a direct hardline coaxial cable connection to an amplifier housing?
AC from a network power supply with a direct hardline coaxial cable connection to an amplifier housing is inserted into the network using the amplifier AC circuitry.
What is the advantage for supplying alternating current (AC) to multiple amplifiers from one network power supply?
Allows the designer to place amplifiers without concern about access to electrical utility power.
In hybrid fiber/coaxial (HFC) networks, where does the sweeping sequence for both the forward and return paths begin?
Although the signals in HFC networks flow in opposite directions, the sweeping sequence for both the forward and return paths begins with the first amplifiers that are downstream from the fiber node.
Dipole antenna
An antenna that consists of an electrical conductor that is split at the center with an insulator so that each conductor can be accessed to transmit or receive a signal.
What enabled the power limitation for network power supplies in broadband cable networks to be increased from 60 volts alternating current (VAC) to 90 VAC?
As cable TV networks evolved into broadband cable networks, National Electrical Code (NEC) Article 830, which defines power limitations for network-powered broadband communications systems, raised the maximum voltage from low-power sources to 100 VAC.
What do normalized reference traces taken at a fiber-node test point establish?
Baseline sweep responses that are used to balance and sweep all the amplifiers serviced by that fiber-node.
What is the source of energy in a standby power supply if the electricity from the local utility is temporarily out of service?
Batteries within the standy power supplies.
Why are network design maps drawn with symbols that represent each of the network elements connected by the various types of cable?
Because using replicas of the actual broadband cable elements on network design maps is inefficient. Network design maps are drawn with symbols that represent each of the network elements connected by the various types of cable.
What is required for checking the physical network integrity when maintaining the coaxial cable network?
Being observant and performing some minor tasks while engaged in regularly scheduled activities.
How does surge protection at the input and output of a ferroresonant power supply defend against voltage surges?
By passing voltage surges (within the surge device rating) to ground without damage.
TDR
Calculates and displays the distance to the cable faults based on the time difference between the sent and reflected pulses along with the characteristics of the cable.
Customer premises
Connected to the network through distribution taps spliced into the coaxial cable.
Which is a benefit of an aggressive signal leakage policy?
Decreased ingress-related service calls.
Leakage detector
Discovers, then measures, broadband cable signals leaking from the network.
When sweeping a line extender, what can be expected due to the distribution taps in the coaxial cable going in and out of the line extender?
Distribution taps in the coaxial cables going in and out of line extenders create amplitude variations in the sweep response
What occurs when a sweep signal level meter (SLM) is normalized?
During normalization, the sweep SLM looks at the raw sweep and compensates for any slope and amplitude variations to display a frequency response that is flat, which is then stored as the reference used to measure the network frequency response.
CableLabs estimates 40% of American households can be reached by an HFC network.
False. CableLabs estimates 90% of American households can be reached by an HFC network.
What technologies are defined in DOCSIS 4.0 to help sustain the hybrid fiber/coax (HFC) network infrastructure for several more years?
Full Duplex DOCSIS (FDX) and Extended Spectrum DOCSIS (ESD).
Why is a dipole antenna used for Federal Communications Commission (FCC) leakage measurements?
Having well known performance characteristics, the half-wave dipole antenna, and the length of its elements, is designed to operate at a specific frequency. At the design frequency and a specific field strength, the half-wave dipole antenna provides a known output signal.
How must a directional test point be installed in an amplifier to enable insertion of upstream sweep pulses and view the downstream sweep?
In a path common to the downstream and upstream.
In a standby network power supply, what switches the power supply into standby operation and converts the battery direct current (DC) to alternating current (AC)?
In a standby network power supply, an inverter switches the power supply into standby operation and converts the battery DC to AC when it senses a power outage or when the incoming voltage drops or rises significantly
In hardline coaxial cable for underground installations, what is the purpose for the flooding compound between the jacket and the sheath?
In hardline coaxial cable for underground installations, the flooding compound seals the cable against corrosive elements in case the jacket is damaged.
What does the term "cumulative" mean in the context of the Cumulative Leakage Index (CLI) reported to the Federal Communications Commission (FCC)?
In the CLI reported to the FCC, the term "cumulative" is used because the calculation is designed to present the overall effect of the leakage in the network.
In the hybrid fiber/coax (HFC) network, what function do splitters and directional couplers in the return path serve?
In the HFC network return path, splitters and directional couplers combine return signals that originate and arrive from separate distribution runs.
What is the distinction between a line extender amplifier and a distribution amplifier?
In the coaxial cable portion of the HFC network, typically there are distribution amplifiers that have multiple downstream outputs and line extenders with one downstream output.
Which of the following problem(s) are caused by egress from a hybrid fiber/coax (HFC) network?
Interference with aeronautical navigation and communication, amateur radio, public service, and cellular communications.
What leakage level must be entered in the leakage log?
Leaks 20 microvolts per meter (μV/m) or higher measured 10 feet from the cable.
What is a likely cause when a sweep response displays a low-frequency roll-off?
Low-frequency roll-off could be caused by a loose seizure screw acting like a capacitor that passes high frequencies while attenuating low frequencies, a defective tap plate, or water inside a tap.
Many cable operators require which type of leaks to be fixed?
Many cable operators have a policy to immediately repair all detected leaks, even those below 20 microvolts per meter (μV/m), which exceeds the FCC requirements.
DMM
Measures AC and DC voltages, resistance for continuity checks, and current.
SLM
Measures analog TV channels, and can quickly measure digital channel parameters and identify network impairments.
In modern sweep systems, what type of nonintrusive and noninterfering test signal is inserted into the downstream?
Narrow-band continuous wave (CW) test carriers, called pulses, at frequencies between channels.
What is a common solution when congestion from modem activity and traffic becomes unacceptable in a hybrid fiber/coax (HFC) network?
Node splitting, the subdividing of serving areas into two or more smaller serving areas.
What advantage is realized by increasing the voltage in a broadband cable network from 60 volts alternating current (VAC) to 90 volts?
Operating with 50% more voltage reduces the voltage drop and current drawn in the network for more efficient power utilization.
What type of network architecture design did the original broadband cable networks use to transport television and audio signals to customer premises?
Originally, broadband cable networks were designed using copper/aluminum coaxial cable in a tree-and-branch architecture to transport television and audio signals to customer premises.
Why is signal leakage interference at long term evolution (LTE) telephone frequencies difficult to prevent?
Preventing leakage interference at LTE frequencies is especially challenging as almost everyone has an LTE phone that can pick up interference from a nearby TV, set-top box (STB), or cable modem connection.
What do the values indicated on the tap face plate by a sticker or number stamped into the housing of an RF distribution tap indicate?
RF distribution tap values indicated on the tap face plate by a sticker or number stamped into the housing is the signal loss (in dB) between the downstream tap input port and the tap (drop) ports
When trying to find the source of a very strong leakage signal, what should be done?
Reduce the sensitivity of the leakage detector or even remove the antenna and allow the connector alone to pick up the leakage signal.
Trunk amplifiers
Several are typically cascaded in series to maintain channel amplitude at useable levels at customer premises farthest from the headend.
What is an effective preventive maintenance practice that is also required by regulating authorities?
Signal leakage monitoring and repair is an extremely effective preventive maintenance practice that is also required by regulating authorities
Egress
Signals that escape or leak from a closed communications system, such as from a cable network, potentially causing interference with other communications systems. Synonymous with leakage.
How do the leakage regulations for quadrature amplitude modulation (QAM) channels differ from analog modulation channels?
Since the QAM channel power levels are required to be below the level of the leakage test signal, the FCC ruled that enacting QAM channel specific leakage monitoring and measurement regulations and methodology is unnecessary.
What does a normalized reference trace from a fiber-node test point eliminate from the sweep process?
Slope and response variations of the headend and optical transport.
When troubleshooting signal leakage in the drop system, what does it mean if all signs of signal leakage disappear when the ground block is disconnected and terminated on the side connected to the customer premises?
Something in the customer premises is the leakage source.
Even though the downstream sweep test pulses are intended to fit in the narrow frequency band between channels, what parameter can cause interference if set too high?
Sweep test pulse amplitude.
Which of the following is true regarding line extenders? Choose all that apply.
Sweeping the upstream through a line extender is the same as performing the same process on a single path in a distribution amplifier. In network designs in which the line extenders have the same sloped downstream output as fiber-node and distribution amplifiers, the same reference trace can be used for response measurements.
What conditions enable an amplifier's forward, downstream output test point to be used to inject test pulses into the upstream?
Test pulses can be injected into the upstream through an amplifier's forward, downstream output test point if the test point is located where the forward and return paths are shared.
Which of the following is true about calculating cumulative leakage index (CLI)? Choose all that apply.
The I∞ method of calculating CLI gives all leaks equal weight. In 2018, the FCC eliminated the I3000 method of calculating CLI in favor of in favor of the more effective I∞ method.
In a hybrid fiber/coax (HFC) network, what term defines the maximum number of cascaded amplifiers in a network design?
The Node +N term defines the maximum number of cascaded amplifiers in a network design. For example, a network designed for a maximum of six cascaded amplifiers is called a Node +6 network, for one fiber node plus six amplifiers.
What inserts alternating current (AC) into the network with a direct connection to an amplifier rather than using a power inserter?
The amplifier AC circuitry.
According to the Federal Communications Commission (FCC) leakage regulations, what distance must an antenna be from the network for leakage level measurements?
The antenna must be 3 meters (10 feet) from the network elements and 3 meters (10 feet) above the ground.
When standing waves are displayed in the sweep response, what does the frequency separation between response peaks indicate?
The approximate distance from the test point to the fault.
In a standby network power supply, what comes online to convert the battery voltage to alternating current (AC), which then goes to the ferroresonant transformer?
The battery-powered inverter.
What is the biggest difference between troubleshooting an issue in the customer drop and the hybrid fiber/coax (HFC) network?
The biggest difference between troubleshooting an issue in the customer drop and the HFC network is the number of customers affected and distances between signal status checks.
What is an amplifier station?
The collective amplifier housing and all internal modules.
What should you be looking for when analyzing the network design maps to troubleshoot a problem?
The device common to those customers affected before traveling to make signal status checks.
What signal level meter (SLM) function can measure digital channel parameters and identify network impairments?
The digital signal analyzer function can quickly measure digital channel parameters and identify network impairments.
When using the triangulation technique to find the source of a leak, why is a dipole antenna used?
The dipole antenna is directional and picks up the strongest signal that is at a right angle, or perpendicular to the antenna elements.
How can a distribution amplifier be identified in the network or on a network design map?
The distribution amplifier has multiple downstream outputs.
Branches in the architecture
The downstream signal is distributed within nearby neighborhoods using 0.412-inch to 0.625-inch diameter coaxial cable, splitters, and directional couplers.
What is the goal when injecting sweep test pulses into an active network?
The goal when injecting test pulses into an active network is to avoid interfering with the channels being transported
When sweeping the upstream return path in a hybrid fiber coax (HFC) network, where are the upstream levels and sweep responses measured?
The headend.
What is done for leak measuring 1.25 microvolts per meter (μV/m) from about 160 feet away from the coaxial cable network?
The leak level is likely 20 μV/m or higher when measured 10 feet from the cable and must be fixed and recorded in the leakage log
When calculating the network cumulative leakage index (CLI), what is done with leaks that are equal to or greater than 50 microvolts per meter (µVm) measured 10 feet from the network?
The leakage values are squared and then added together, then multiplied times a factor based on how much of the network was tested in 90 days.
How can a less-experienced technician identify what non-standard symbols on the network design maps represent?
The legend at the bottom of the network design map that defines the map symbols, cable types, and amplifier data.
Which part of a ferroresonant transformer regulates the load on the secondary winding?
The magnetic shunt.
In an HFC network, what is the area defined as power realm?
The physical area defined by cable resistance, combined amplifier load requirements, individual amplifier voltage minimums, and limits on total AC current.
What features of other network architectures appear to be major advantages over the hybrid fiber/coax (HFC) network architecture?
The seemingly infinite bandwidth of passive optical networks (PON) and the wireless accessibility of 5G networks appear to be major advantages over the HFC network architecture.
What is the RF distribution tap value indicated on the tap face plate by a sticker or number stamped into the housing?
The signal loss between the tap downstream input port and the tap ports.
What are the three main components of a typical standby power supply?
The typical standby power supply has three main elements, 1) a ferroresonant transformer that transforms the utility 115 VAC to the 60 or 90 VAC output voltage, 2) a set of batteries acting as a backup power source, and 3) an AC inverter that converts the DC battery backup power to a 60 or 90 VAC output
How is the voltage drop across the cable loop resistance derived?
The voltage drop across the cable loop resistance is derived from Ohm's law, E = I x R, in which E is the voltage drop, I is the current through the cable, and R is the cable loop resistance.
What test instrument sends out a test signal and displays any reflections caused by impedance mismatches in the cable that are characteristic of cable faults?
Time domain reflectometer (TDR)
What is a good practice to ensure accurate sweep measurements?
To ensure accurate sweep measurements, it is good practice to store a new reference trace at the fiber node before beginning to sweep each day and when sweeping areas served by a different fiber node.
What do many standby power supplies have to optimize the lifespan of the batteries?
To optimize the lifespan of the batteries, most standby power supplies have multiple battery charging modes.
In a power inserter with three filtering networks, what is the purpose of the high-pass filter?
To prevent the 60 hertz (Hz) alternating current (AC) from passing between the two radio frequency (RF)/AC ports.
Why is the main downstream output/upstream input port of a distribution amplifier typically the first to be swept in the downstream direction?
To select equalizers and set the output amplitude levels.
DOCSIS 4.0 offers Full Duplex DOCSIS (FDX) and Extended Spectrum DOCSIS (ESD) to help HFC networks compete with passive optical network (PON)
True
An advantage an HFC network offers over passive optical network (PON) architectures and the wireless access of 5G networks is PONs are costly to build and 5G networks are bandwidth limited.
True.
Ingress
Unwanted signals entering a broadband cable network that cause interference to desired signals, often as a result of poor shielding or faulty connections.
When performing preventive maintenance on a network power supply, why should the electrical connections be checked?
When performing preventive maintenance on a network power supply, check the electrical connections, which become loose over time due to vibration or temperature changes
When sweeping a distribution amplifier with multiple active downstream ports, which port is typically the first to be swept?
When sweeping a distribution amplifier, the main downstream output/upstream input port, which is always active, is typically the first to be swept in the downstream direction to select equalizers and set output amplitude levels.
What is the input voltage at an amplifier when the source voltage is 90 volts alternating current (VAC) and the voltage across the loop resistance in front of the amplifier is 2.5 V?
When the source voltage is 90 VAC and the voltage across the loop resistance in front of an amplifier is 2.5 V, the amplifier input voltage is 90 - 2.5 = 87.5 VAC.
When does the shape of the quasi-square waveform from a ferroresonant network power supply resemble a sine wave?
With a full 15-ampere (A) load, the shape of the quasi-square waveform from a ferroresonant network power supply resembles a sine wave.
In the tree-and-branch architecture, how is the downstream signal from the trunk fed to the distribution branches?
Within each trunk amplifier, a portion of the downstream is fed to a bridger amplifier to boost the signal before being split and routed to the distribution branches.
