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ROC 2 PART 2 Revised Questions and
Answers / Sure A +
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. Triangulation - ✔✔A signal leakage-finding technique in which the intersection of an imaginary line drawn at a right angel from two separate dipole antenna locations identifies the leakage source. Near-field probe - ✔✔A short antenna fixed at the end of a connector cable that allows for close-in measurements in places such as attics or crawl spaces; signal leakage antenna that provides the most narrowly focused measurement and the greatest accuracy, often used in confined areas such as attics or crawl spaces. 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. Which is a benefit of an aggressive signal leakage policy?• - ✔✔Decreased ingress-related service calls. 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. 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. 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.
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. 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. 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 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. What geometric shape is a sine wave based upon? - ✔✔• A right-degree triangle. What are the three elements of a carrier wave that can be manipulated? - ✔✔• Amplitude, frequency, and phase. What are the peaks and minima of the amplitude modulation (AM) waveform envelope related to? - ✔✔• The amplitude of the modulation signal. In a hybrid fiber/coax (HFC) network what type of crude amplitude modulation (AM) detector causes common path distortion (CPD)? - ✔✔• An envelope detector. In a conventional amplitude modulation (AM) transmission, how much power is in the sidebands and how much is in the carrier? - ✔✔• Two-thirds of the power is in the carrier with one-third in the sidebands. Why can Carson's Rule be used to determine the bandwidth of a frequency modulation (FM) carrier?
- ✔✔• In most cases, the amplitude of the sidebands furthest from the carrier frequency are so low that they can be ignored.
What is used in some receivers to remove all attenuation before the amplifier until the received signal level reaches a designed threshold? - ✔✔• Delayed automatic gain control (AGC). Which class of amplifier utilizes a push-pull amplifier configuration in which each transistor conducts current during opposite cycles of the input signal? - ✔✔• Class B amplifier. Which class of amplifier has an output that is very high in harmonics and must be attenuated by a filter network? - ✔✔Class C amplifier. Which class of amplifier efficiency approaches, but never achieves, 100%? - ✔✔• Class D amplifier. Ferroresonant - ✔✔A power supply technology that uses the non-linear inductance of a transformer with a resonate capacitor to effectively operate with a steady output voltage with changing input voltages. What characterizes N-doped silicon that is used in bipolar junction transistors (BJT)? - ✔✔• N-doped silicon has an excess of free electrons compared to P-doped silicon. What is another name for the bipolar junction transistor (BJT) common collector configuration? - ✔✔• Emitter follower. In what application would a bipolar junction transistor (BJT) common base configuration be used? - ✔✔• For impedance isolation between a low-impedance device and high-impedance amplifier. Calculating the signal voltage and current range on the output of a bipolar junction transistor (BJT) involve repeated applications of what? - ✔✔• Ohm's law. In a basic N-channel junction field effect transistor (J-FET), what when negative bias is applied to the gate? - ✔✔• The J-FET depletion region is expanded, decreasing the current that is transported between the source and the drain. Why do metal oxide semiconductor field effect transistors (MOSFET) have internal zener diodes from the gate to the source or substrate? - ✔✔• To prevent damage from static electricity.
In an N-channel enhancement mode metal oxide semiconductor field effect transistor (MOSFET), what effectively turns the P substrate between the two wells into an induced N-channel? - ✔✔• A suitable positive voltage placed between the gate and the source. What is a consequence of high-speed charging and discharging of the capacitance in a complementary metal oxide semiconductor (CMOS)? - ✔✔• Power is dissipated as heat. How does complementary metal oxide semiconductor (CMOS) technology combat capacitance in a circuit? - ✔✔• It combines N-channel and P-channel metal oxide semiconductor field effect transistors (MOSFET) onto a single substrate. What logic family of bipolar transistor logic circuits is used extensively where the fastest speeds are required at the expense of power dissipation? - ✔✔• Emitter coupled logic (ECL). What enables the collector current in an operational amplifier's differential amplifier to be independent of the two input voltages, VI+ and VI-? - ✔✔• DC bias circuitry in the differential amplifier emitter circuit. What determines the voltage gain of an operational amplifier (op amp) inverter? - ✔✔• The value of the input and feedback resistors. In an operational amplifier (op amp), what is a common practice to minimize voltage offsets at the inputs to an inverter? - ✔✔• Make the net DC resistance the same on both inputs to the op amp. In an operational amplifier (op amp), what is open-loop gain? - ✔✔• The pre-determined gain of the op amp without feedback. What distinguishes an operational amplifier (op amp) configured as a voltage follower with gain from an inverter circuit? - ✔✔• The input signal in the voltage follower with gain goes to the non-inverting input (+). In an operational amplifier (op amp) summing amplifier circuit, how can unequal weights be given to the signals being summed together? - ✔✔• By using different value input resistors for each signal.
What benefit does a power-doubling configuration offer compared to a single cascade push-pull hybrid amplifier? - ✔✔• Twice the output with the same distortion. How does feed-forward amplifier technology achieve distortion reduction that is better than power- doubling? - ✔✔• By introducing delay lines and error amplifiers. 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. 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 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). 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. 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. How can a distribution amplifier be identified in the network or on a network design map? • The distribution amplifier has multiple downstream outputs. 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. 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 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 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. Monochromatic - ✔✔A narrow range of wavelengths which result in the appearance of only one color. Coherent - ✔✔RF and optical waves which are the same frequency and phase. Photodetector - ✔✔An optoelectronic device that transforms light energy into electrical energy Chromatic dispersion (CD) - ✔✔A characteristic of all optical fiber that causes transported pulses of light to spread out and overlap before they reach the receiver, hindering the receiver's ability to interpret data and causing bit errors in high-speed data transmissions. Bragg grating - ✔✔An optical fiber segment with lines etched to create different refractive indexes causing some wavelengths to be reflected, and other wavelengths to pass through. Why are Velcro straps preferred over standard plastic tie wraps when bundling pigtails for storage in a splice panel? - ✔✔Because Velcro straps are removable and can hold the pigtails together without placing undue strain on the optical fibers. The current produced by an optical detector when there is either no optical signal or the signal is below the detector's minimum input level. - ✔✔Dark Current What functions does the detector in an optical receiver perform? - ✔✔Conversion of an optical carrier to an electrical signal, and demodulation of the modulated optical carrier. Which standards organization is considered to be the creator of the world's most recognized communications standards, known as recommendations? - ✔✔• The International Telecommunication Union (ITU). In which component in a fiber-optics communication system do changes to the intensity of the optical signal occur? - ✔✔• The optical
Ethernet - ✔✔Ethernet is a family of Institute of Electrical and Electronics Engineers (IEEE) 802. standards that deal with the transmission of digital packets Acceptance test - ✔✔Length and loss test of fiber-optic cable that is typically performed twice— when the cable is received from the manufacturer and after the cable is installed and spliced into the network. Mode field diameter (MFD) - ✔✔The measure of the spot size or beam width of light propagating in a single-mode fiber. The vast majority of the optical power propagates within the fiber core, and a small portion, up to 20%, may propagate in the cladding near the core. Cleanliness - ✔✔Cleanliness is the single most important issue facing the technician during splicing. Monitoring the status of optical nodes - ✔✔Involves the use of a node transponder that continuously monitors a number of critical functions. Digital return path transmissions - ✔✔Use dense wavelength division multiplexing (DWDM) digital return transmitters in hub-to-headend architectures. Broadband cable operators provide customers with high-speed data (HSD) connections to the Internet via their HFC networks using what standard? - ✔✔Data Over Cable Service Interface Specification (DOCSIS). What is MPEG (Moving Picture Experts Group)? - ✔✔A universally accepted standard for digital television, first released in 1992. Which of the following is true about optical nodes? - ✔✔They contain four main sections: the optical receiver, the RF amplifier module, the reverse optical transmitter, and the DC power supply. What product based on the Data Over Cable Service Interface Specification (DOCSIS) defines the protocols for Internet protocol (IP) telephony over hybrid fiber/coax (HFC) networks? - ✔✔PacketCable. In a centralized server video-on-demand (VOD) architecture, - ✔✔The number of servers needed for video content storage is smaller than in the distributed server architecture.
Which of the following statements about local ad insertion is true? - ✔✔Local ad insertion is performed usually by a video server. In regard to providing high-speed data (HSD) service, - ✔✔The cable modem termination system (CMTS) can provide a data transfer rate up to 38 Mbps, using 256-QAM in a single 6 MHz channel. Which of the following is true about the synchronous optical network (SONET) transmission standard? - ✔✔SONET is the North American standard used for telephony applications. Why was the zero-dispersion point in single-mode fiber moved to 1,550 nm? - ✔✔To take advantage of the low intrinsic absorption and lower attenuation at 1,550 nm in single-mode fiber. What type of single-mode fiber is intended for fiber-to-the-home (FTTH) installations? - ✔✔The ITU- T G.657 bend-insensitive fiber (BIF). What are the primary causes of intrinsic loss in single-mode fiber? - ✔✔Material absorption and Rayleigh scattering. The phenomenon, total internal reflection, is what enables an optical fiber to guide light. What characteristic of optical fiber causes total internal reflection? - ✔✔The difference in refractive indexes, between cladding and core, causes light to be reflected off the cladding and back into the core along the optical fiber. Where would you expect Fresnel reflections to occur in a fiber-optic network? - ✔✔At connections and mechanical splices where the signal source is entering or exiting the cable. Chromatic dispersion is a combination of which two dispersions? - ✔✔Material and waveguide dispersion. What is one advantage and one disadvantage of single-mode fiber with a large mode field diameter (MFD)? - ✔✔The larger the MFD, the easier it is to splice and connectorize the fiber, although it becomes more sensitive to bending losses.
What is the purpose of buffer tubes in fiber-optic cable? - ✔✔Buffer tubes protect and separate the optical fiber in smaller bundles. When splicing fiber-optic cable, why is it a good safety practice to clean off fiber strippers and other hand tools after each use? - ✔✔To prevent the accidental transfer of fiber debris or fiber chips onto clean hands. Where would you expect to install a mid-entry splice in a fiber-optic cable network? - ✔✔A location where a select number of optical fibers need to be spliced, and the remaining buffer tubes and fibers remain untouched. Dead zone box - ✔✔Connected between the OTDR and the fiber under test, this device effectively fills the OTDR dead zone with a known good piece of fiber (in the box) so even the beginning of the fiber under test can be properly seen on the OTDR trace Optical time domain reflectometer (OTDR) - ✔✔A test instrument that injects light waves into an optical fiber, and then displays the reflected light's amplitude and length of time to return, which is used to measure the length and attenuation of optical fiber and pinpoint the presence of any connectors, splices, or faults. Neutral density filter - ✔✔An optical filter that decreases the intensity of light without changing spectral distribution or wavelength of the light, aka, gray filter. Angled physical contact (APC) - ✔✔A technique of polishing a fiber and/or connector ferrule with an 8 - degree endface to minimize reflective light How do technicians know the specific type of single-mode fiber used in a particular project? - ✔✔They have read the project's specification records. Which type of fiber-optic cable provides the most stable transport characteristics and additional protection from stresses caused by macrobends and microbends? - ✔✔Loose-tube cable. What is a consideration for the use of ribbon fiber? - ✔✔Ribbon fiber requires different tools and equipment to perform splicing.
What are the two critical elements that align the optical fibers in a connection? - ✔✔The ferrules and the mating adapter. In an optical network, what is reflectance? - ✔✔Reflectance is the reflected light from a single Fresnel reflection event. How should surface particulates usually be removed from optical connectors? - ✔✔By using a compressed-air cleaner designed for optical connectors. Since they provide the same functions, what is the primary difference between the fiber distribution hub (FDH) and fiber access terminal (FAT)?. - ✔✔The FAT is typically easier to install and has lower fiber counts than the FDH. Which statement about pigtails used for optical fiber terminations is true? - ✔✔Prior to splicing, pigtails should be labeled to correspond with the correct color code and patch panel designation. How are optical splitters used in the forward path? - ✔✔In the forward path, optical splitters are used as passive branching devices that divide an optical signal across multiple output fibers. Which optical splitter package is similar in appearance and size to a standard fusion splice protector?
- ✔✔Fused biconical taper (FBT). Cleave - ✔✔A controlled break in an optical fiber that results in a clean, flat surface on the end of the fiber that is perpendicular the fiber's length. Concentricity - ✔✔The measurement of the location of a conductor or optical fiber core with respect to the absolute center of the circular insulation (wire) or cladding (optical fiber). Micron (μm) - ✔✔A micrometer: The equivalent of one one-millionth (1 × .000001) of a meter. Which type of fusion splicer is ideal for fiber-to-the-x (FTTx) splicing? - ✔✔The fixed V-groove splicer.
The National Electrical Safety Code (NESC) provides guidelines concerning which portion of the fiber- optic cable network? - ✔✔Minimum safety clearances between different conductors of overhead and underground electric supply and communications lines. What is a safety concern when aerial fiber-optic cable is installed between poles, even though there are no high-voltage power lines? - ✔✔The buildup of lethal amounts of static electricity on the fiber- optic cable that can discharge through a person on a ladder or some other conductor connected to ground. What is used in outside plant fiber-optic cable to protect and isolate the optical fibers from stress? - ✔✔Strength members and buffer tubes. What is the purpose of grounding to earth? - ✔✔To protect against the adverse effects of lightning and assist in the reduction of static.inbound and outbound span. What information is documented at fiber-optic slack and splice locations? - ✔✔Incoming and outgoing sequential markings showing the cable's physical length. What can be attached to the pulling line to prevent the fiber-optic cable from twisting during installation? - ✔✔A break-away swivel. What are two critical factors for a successful installation of fiber-optic cable? - ✔✔Cable pulling tension and cable bend radius. What should be done to prevent the buildup of lethal amounts of static electricity on long lengths of aerial fiber-optic cable? Install grounding clamps, which connect the cable exterior and metallic messengers to a good solid ground at each pole site. - ✔✔Install grounding clamps, which connect the cable exterior and metallic messengers to a good solid ground at each pole site. When working on a ladder, which rungs are forbidden for standing? - ✔✔The top two rungs of any ladder. Optical network unit/optical network terminal (ONU/ONT) - ✔✔Generic term for the device containing two modules, the ONU, which connects the customer premises to the optical distribution network (ODN). The second device, the optical network terminal, provides the electrical interfaces to the customer premises equipment (CPE).
Passive optical network (PON) - ✔✔The generic term for the point-to-multipoint (P2MP) networks that utilize fiber-to-the-premises (FTTP) topology. What is an example of transport media in a telecommunications network? - ✔✔Coaxial cable. Which answer best describes network topology? - ✔✔It's a sub-layer of network architecture that describes the physical and logical configuration of connected elements between the signal source and the network termination elements. What does a point-to-multipoint (P2MP) topology consist of? - ✔✔A P2MP topology consists of a host element connected through a splitter or optical coupler to two or more receiving elements. Which type of network topology allows troubleshooting a problem or switching around the problem to be accomplished easily from the central hub? - ✔✔Star. Which type of network topology has been focused primarily on alternative routing around cities and industrial areas? - ✔✔Ring. What is one reason why broadband cable operators install fiber-optic cable in stages instead of changing the infrastructure all at once? - ✔✔Changing the infrastructure all at once would cause too many service disruptions. What is the difference between the fiber-to-the-node (FTTN) and fiber-to-the-curb (FTTC) topologies? - ✔✔An FTTC is allowed a smaller number of RF amplifiers between the optical fiber and the customer premises. What type of fiber-to-the-x (FTTx) topology does a passive optical network (PON) use to make a point-to-multipoint (P2MP) fiber-optic cable connection between the broadband cable headend and the customer premises? - ✔✔Fiber-to-the-home (FTTH). In a passive optical network (PON), which category of fiber-optic cable is routed from the headend into the optical distribution network (ODN)? - ✔✔Trunk.
Select the answer that best completes this sentence: In analog modulation, the _____ of the light wave changes in _____ proportion to the _____ analog signal. - ✔✔Intensity; direct; incoming. Which type of optical detection involves a photodiode that converts the light waves to an electrical signal that varies in proportion to intensity changes in the light waves? - ✔✔Direct. Which layer of a synchronous optical network (SONET) maps the signals into a synchronous payload envelope (SPE)? - ✔✔Path. The frame structure of a synchronous transport signal (STS) is divided into two parts. What are they?
- ✔✔The transport overhead, which contains the section and line layers, and the synchronous payload envelope, which contains the path overhead and the payload data. What occurs in the wavelength division multiplexing (WDM) process? - ✔✔The optical output from multiple lasers operating at different wavelengths is combined and transported over a single, common optical fiber. In what type of installation is wide wavelength division multiplexing (WWDM) used? - ✔✔It is used in passive optical networks. Coarse wavelength division multiplexing (CWDM) applications were expanded to include use in what band, where a large OH absorption loss occurred with older single-mode fibers? - ✔✔E-band. What is one element used in the transmission and reception of dense wavelength division multiplexing (DWDM)? - ✔✔High-quality, temperature cooled distributed feedback lasers. Optoelectronics - ✔✔Any technology that responds to light waves or is used in a fiber plant, such as a laser, photodiode, optical coupler or amplifier, etc. What are the main elements of an optical transmitter? - ✔✔Data encoder/modulator, electrical interface, laser, optical interface. What is one process that has to happen before digital modulation can occur in an optical transmitter? - ✔✔The data must be encoded.
In networks transporting data rates that are higher than _____, Fabry-Perot (F-P) lasers are considered inadequate. - ✔✔2.5 Gbps. Why are the amplitude levels into an optical transmitter different between analog television and quadrature amplitude modulation (QAM) carriers? - ✔✔Because analog carriers have a video sync pulse, which can be used to set amplitude. QAM carriers don't have a sync pulse; the average power of the carrier is used to adjust the QAM carrier's amplitude. What are the main elements of an optical receiver? - ✔✔Demodulator, electrical interface, optical detector, optical interface. A technician is determining whether the optical power into an optical receiver is within the acceptable dynamic range. He finds that the optical power is too high, but the loss budget agrees with the design. What should he do to optimize the optical power in this situation? - ✔✔Install an optical attenuator. Typically, what is the first step to take when adjusting an optical receiver? - ✔✔Turn on the optical receiver. Which type of optical amplifier produces no measurable distortion to the modulated light wave? - ✔✔Erbium-doped fiber amplifiers (EDFA). Which component of a digital optical network is used to receive digital modulation light waves and convert them to an electrical signal? - ✔✔Optical transponder. Which type of optical coupler provides the least amount of insertion loss? - ✔✔Fused. Saturation point - ✔✔The level in which an amplifier stops boosting the input signal and the output becomes nonlinear and excessive distortion is generated. Which category of fiber-optic cable design typically uses some variation of the star topology? - ✔✔Signal distribution. What is the ideal way for a broadband cable network designer to plan the replacement of coaxial cable with fiber-optic cable to shorten amplifier cascades? - ✔✔Use the existing coaxial network infrastructure.
