Roc Fundamentals
Calculate the capacitive reactance of a power inserter's feed-through capacitor when: (1) the frequency is 60 Hz; and (2) the capacitance value is 1,000 pF.
(answer) 2.65 MO.
According to the FCC, leaks _____ and above measured _____ feet from the cable must be logged and repaired.
(answer) 20 µv/m, 10
1:5 ratio is equal to
(answer) 20%
A signal increase of 1 dB represents a __________ increase in power.
(answer) 25.89%
How many decimal values can eight bits of data represent?
(answer) 256
You are planning a fiber-optic network and want to amplify the signal so you can send it farther into the field. At which wavelength must the laser emit?
(answer) 1,550nm
What are the symptoms of hum on an upstream digital modulation channel?
(answer) Bit errors occur, similar to impulse noise and ingress on the upstream path.
An RF/AC bypass tap
(answer) Has the added feature of being able to maintain RF signal and AC voltage continuity during faceplate removal.
The three networks of the PacketCable 1.0 architecture are
(answer) The DOCSIS HFC (hybrid fiber/coax) access network; the managed IP network; and the PSTN.
When is UTP cable preferred over STP?
(answer) When there is little electrical interference.
A 1 mV decrease in a signal level of 40 dBmV is approximately equivalent to a decrease in level of
(answer) 0.1db.
Which testing device is the best to use to measure cable faults?
(answer) A time domain reflectometer (TDR).
A fraction is converted to a percent by
(answer) Dividing the numerator by the denominator and multiplying by 100.
Most line extender housings have
(answer) One input port for receiving the forward RF signals and one or two output ports for distributing the amplified forward RF signals.
The input-to-output power ratio of a coaxial cable that has 1DB of attenuation is
(answer) 1.2589:1.
In a DOCSIS 3.1 orthogonal frequency division multiple access (OFDMA) upstream channel, the average power of the subcarriers are normalized to what bandwidth?
(answer) 1.6 MHz.
The input-to-output power ratio for 2 bels of similar impedance cable is
(answer) 100.1
Which of the following are the aeronautical frequency bands?
(answer) 108-137 and 225-400 mHz.
How much signal is necessary from the subscriber's tap port @ 750 MHz to provide a minimum of 3.0 dBmV to the TV set when the drop is 150 feet of Series 6 cable and just one outlet use 5.65 dB per 100 feet for the attenuation rate and round off to nearest tenth of a dBmV?
(answer) 11.5 dBmV.
The code words and spreading algorithm of synchronous code division multiple access (S-CDMA) enable simultaneous transmission of up to how many modems on the same RF return channel?
(answer) 128
How much signal is needed from the subscriber's tap port @ 750 MHz to provide a minimum of +3.0 dBmV to each of the TV sets when there is 132 feet of Series 6 cable and a two-way splitter? Use 5.65 dB per 100 feet for the Series 6 cable attenuation rate and 4.0 dB for the splitter attenuation.
(answer) 14.5 dBmV.
The power ratio for 2 DB is
(answer) 1:1
The terminating tap
(answer) Is the last tap installed at the end of the feeder cable run.
When the output of a line extender is 3 dB lower than it normally should be,
(answer) The signal is 3 dB lower than normal from that point on.
Which advanced Physical Layer (PHY) technology developed and added to DOCSIS 2.0 includes byte interleaving?
(answer) Advanced time division multiple access (A-TDMA).
Which of the following automatically captures the location of leakage data right down to the street address?
(answer) GPS-assisted leakage measurement instruments.
What is ingress?
(answer) Signals leaking into the cable system.
Values expressed in dBmV progress in a nonlinear fashion when compared to a linear mV scale because
(answer) They are based on the logarithms of power ratios.
The output port RF signal level is ______________ dBmV at 55.25 MHz and the tap port signal level is _______________ dBmV at 55.25 MHz for a two-way feed-through tap when: (1) the input port signal level is 30.5 dBmV at 55.25; (2) the insertion loss is 3.3 dB at 55.25 MHz; and (3) the tap loss is 7.6 dB at 55.25 MHz.
(answer) 27.2 and 22.9
An input-to-output power ratio of 10:1 has an input-to-output voltage ratio of
(answer) 3.162:1, the square root of the power ratio.
When calculating return path attenuation in the drop system, what is the attenuation loss through the hot-leg of an unbalanced three-way splitter at sub-split frequencies?
(answer) 3.5
What is the uV/m level of a -37 dBmV signal leakage measurement at 127.2625 MHz?
(answer) 37.75 uV/m.
The impedance of coaxial cable or a device is made up of the combined effects of which three electrical properties?
(answer) Resistance, inductance, and capacitance.
Which of the following devices is an active device?
(answer) An addressable tap.
What are the FCC requirements regarding leakage monitoring?
(answer) Quarterly monitoring and annual reporting.
Which of the following is true?
(answer) To calculate the directional coupler's output port and tap port signal levels in dBmV, first obtain the manufacturer's specifications for insertion losses.
Why does the output level from customer premises equipment (CPE) vary?
(answer) To compensate for variable amounts of attenuation in the return path of each device.
In a fiber-optic cable, what is the purpose of the cladding?
(answer) To guide light down the fiber.
A typical power inserter faceplate
(answer) Contains electronic components, cover bolts, and interconnect pins.
Chipsets with ingress cancellation algorithms are most effective for removing impairments in what portion of the RF return frequency spectrum?
(answer) Within the upstream channel bandwidth.
When using a digital signal analyzer to troubleshoot data throughput in the Data Over Cable Service Interface Specification (DOCSIS) network, what is the minimum modulation error ratio (MER) into the cable modem for a 256-QAM carrier?
(answer) 32 dB or greater.
What is the output port signal level at 547.25 MHz for a directional coupler when: (1) the input signal level is 35.0 dBmV at 547.25 MHz; (2) the output port insertion loss value is 1.4 dB at 547.25 MHz and 0.7 dB at 55.25 MHz; (3) the tap port insertion loss value is 16.2 dB at 547.25 MHz and 15.9 dB at 55.25 MHz; and (4) the tap to output port isolation value is 18 dB at both 547.25 MHz and 55.25 MHz?
(answer) 33.6 dBmV.
What is the return signal pass band frequency used in most of North America?
(answer) 5-42 MHz.
What is the AC input voltage of a power inserter when: (1) the cable between the power supply and the power inserter is 200 feet long; (2) the power supply cable's DC loop resistance is 1.07 ohms/1,000 feet; (3) the power supply output voltage is 60 VAC; and (4) the total current requirement is 11.4 amps?
(answer) 57.56 VAC.
What would be the downstream throughput if two 256-QAM channels with a throughput of 38 megabits per second (Mbps) were bonded?
(answer) 76 Mbps.
What is the tap port RF signal level at 547.25 MHz for a four-way terminating tap when: (1) the preceding tap's output port signal level is 25.0 dBmV at 547.25 MHz; (2) the cable length between the two taps is 110 feet; (3) the cable loss rate specification is 1.82 dB/100 feet at 550 MHz and 0.54 dB/100 feet at 50 MHz; and (4) the tap loss is 14.2 dB at 547.25 MHz?
(answer) 8.8 dBmV.
A length of coaxial cable that has an attenuation of 10 DB will experience an RF signal power loss of ___, with __ of the signal remaining.
(answer) 90% 10%
In addition to being accurate and detailed, a successful troubleshooter knows that
(answer) A critical step in troubleshooting is verifying the signal levels and signal quality at the tap to establish the baseline performance for the installation.
A number that compares an amount that is less than the whole to the whole amount is
(answer) A fraction.
Why is a leakage detector preferable to a signal meter for detecting leakage?
(answer) A leakage detector has an increased sensitivity to weak signals.
What system is a byproduct of the "funneling effect "?
(answer) A many-to-one system.
When aligning the optical return path, what are the ideal characteristics of the test signal injected into the upstream optical transmitter?
(answer) A noise signal of the same bandwidth to be used for upstream transport.
As you prepare to set up the fiber-optic network, you realize you need a coupler that will allow any of its ports to be used as either input or output. Which coupler should you choose?
(answer) A reflective star coupler.
What can be used with a signal level meter (SLM) to check the drop system for RF continuity at sub-band frequencies?
(answer) A signal generator.
The leakage detector's calibration can be verified using the system's leakage carrier, a signal level meter, and
(answer) A variable attenuator.
What media access control (MAC) protocols are specified for digital set-top boxes (STB)?
(answer) ALOHA and time division multiple access (TDMA).
What access schemes were introduced with advanced Physical (PHY) Layer technologies in DOCSIS 2.0?
(answer) Advanced time division multiple access (A-TDMA) and synchronous code division multiple access (S-CDMA).
The return amplifier
(answer) Amplifies the return signals for transmission to the next return amplifier upstream relative to the forward path.
A passive component that reduces signal amplitude equally at all frequencies in a distribution amplifier is
(answer) An attenuation pad.
_____________________ is a short length of fiber that serves as an amplifier in fiber-optic networks, allowing light signals to travel farther while retaining signal strength.
(answer) An erbium-doped fiber amplifier (EDFA).
What is the function of an interdiction unit?
(answer) An interdiction unit controls the level of service to the drop ports it contains.
How does the signal attenuation through coaxial cable in the sub-band frequency spectrum compare to the attenuation at forward path frequencies?
(answer) At sub-band frequencies, the signal attenuation is significantly less than in the forward path.
What location in the network is common path distortion (CPD) most severe?
(answer) At the output of a forward amplifier because the forward levels are highest and the return levels are lowest.
Why is using dBmV, a voltage measurement, acceptable to express the power per Hz power allocation across the channel bandwidth?
(answer) Because a constant 75-ohm impedance is being used.
Why are the data throughput rates for both downstream and upstream in Data Over Cable Service Interface Specification (DOCSIS) networks asymmetrical?
(answer) Because the narrower bandwidths and lower orders of modulation for the return path carriers cause the DOCSIS downstream and upstream data rates to be unequal or asymmetrical.
Where should the injected sweep pulses be placed to avoid interference with active return carriers when sweeping the return path?
(answer) Between active return carriers only if there is adequate space to accommodate the bandwidth of the injected sweep pulses
How is laser clipping in the return path characterized on a spectrum analyzer?
(answer) By an elevated noise floor above 42 MHz after the optical signal has been converted back to RF, typically in the headend.
How can the amount of thermal noise added to a network be minimized?
(answer) By ensuring that the RF input is at or above the specified minimum input level to all amplifiers.
On cable system design maps, standard symbols include a
(answer) Circle for a two-way tap, a square for a four-way tap, and a hexagon for an eight-way tap.
In a Data Over Cable Service Interface Specification (DOCSIS) network, why is the data throughput over the return or upstream path typically less than the throughput of data over the forward or downstream path?
(answer) Compared to the downstream path, the narrower bandwidths and lower orders of modulation used to transport data over the return path cause the downstream and upstream data throughput to be unequal or asymmetrical.
What criteria does the Data Over Cable Service Interface Specification (DOCSIS) certification process ensure?
(answer) Compliance with the DOCSIS standard and interoperability between suppliers.
What should be done before diagnosing a return path problem in the drop system?
(answer) Confirm that the hybrid fiber/coax (HFC) network is working properly.
A constant bit rate (CBR) telephone system is considered to be circuit-switching technology because the analog audio signal is
(answer) Converted into a digital DS0 circuit and switched to other cable telephony customers or to the telephone company's network.
Which Data Over Cable Service Interface Specification (DOCSIS) version was the first to provide an option for raising the top frequency of the upstream spectrum to 85 MHz in order to create enough bandwidth for upstream carriers from modems running on previous DOCSIS versions?
(answer) DOCSIS 3.0
The purpose of PacketCable is to
(answer) Define the architecture for the delivery of real-time IP applications with service levels comparable to POTS.
What evolved after the introduction of switched digital video (SDV) illustrated some limitations of legacy hybrid fiber coax (HFC) networks?
(answer) Distributed access architecture (DAA).
A minimum acceptable signal level of 0 dBmV at a TV set input.
(answer) Equals 1 mV across 75 ohms.
As cable companies have expanded their use of fiber-optic cable, they have also brought it closer to the customer premises, increasing the bandwidth available to customers. Which answer below best represents the progression of fiber-optic network architecture?
(answer) Fiber-to-the-feeder (FTTF), fiber-to-the-neighborhood (FTTN), fiber-to-the-curb (FTTC), fiber-to-the-home (FTTH).
Which of the following statements is true?
(answer) For each power inserter, the system design must ensure that: (1) the current required by any one RF/AC port does not exceed that port's power-passing specification; and (2) the current required by both RF/AC ports does not exceed the AC input port power-passing specification.
House amplifiers with a passive return path are used for what type of situation?
(answer) For situations when long service drops are used and the forward path needs to be amplified but return path amplification is unnecessary.
From where do Data Over Cable Service Interface Specification (DOCSIS) modems receive their configuration files, billing system messages, and access control messages?
(answer) From the cable modem termination system (CMTS) acting as a "proxy" or messenger that transfers messages and files between the modems and the respective servers.
A directional tap that feeds a signal through to other taps.
(answer) Has a directional coupler portion that efficiently routes most of the signal to the output port while removing a small amount of signal and passing it to the splitter network.
In following the six-step troubleshooting process, one of the first pieces of information to establish is
(answer) How many customers are affected in order to identify the issue to a specific customer premises or multiple customers.
How does Internet protocol (IP) multicast differ from IP broadcast?
(answer) IP multicast traffic is only sent to specific modem addresses on the network; IP broadcast traffic is sent to all modems on the network.
What Internet protocol (IP) address modes can a Data Over Cable Service Interface Specification (DOCSIS) 3.0 and 3.1 modem be provisioned in?
(answer) IP version 4 (IPv4), IP version 6 (IPv6), alternate provisioning mode (APM), and dual-stack provisioning mode (DPM).
When should a preamplifier be used to measure impairments with a spectrum analyzer?
(answer) If the noise floor drops less than 10 dB when the input signal is removed from the spectrum analyzer.
How is impulse noise characterized when viewed on a spectrum analyzer?
(answer) Impulse noise will appear as random spikes of energy across the entire return path frequency spectrum (5 to 42 MHz).
What distinguishes a micro-reflection from other types of signal reflections?
(answer) In Micro-reflections, the echoed signals arrive back at the source with a time delay relative to the incident or transmitted signal, ranging from nanoseconds (ns) to a few microseconds (us).
In what applications are avalanche photodiodes (APD) most likely to be used?
(answer) In fiber-to-the-home (FTTH) architectures where the high attenuation of optical splitters must be overcome.
Which of the following statements is true?
(answer) In general, the closer the tap is to the amplifier output port, the higher the tap value.
What signal leakage information and measurements must be included with the annual reporting to the FCC?
(answer) Information carried on signals in the aeronautical bandwidths.
The signal power level in a directional coupler
(answer) Is greater at a 7 dB tap port than at a 12 dB tap port with the same input signal level.
When light strikes a medium at an angle less than the critical angle, what happens to the light?
(answer) It is reflected.
Which of the following describes a power inserter?
(answer) Its specifications for power passing, isolation, and insertion loss are identical to those specifications for splitters and directional couplers from the same manufacturer.
What layers of the Open Systems Interconnection (OSI) reference model are applied between Data Over Cable Service Interface Specification (DOCSIS) modems and the cable modem termination system (CMTS)?
(answer) Layers 1 through 4 Physical layer, Data Link Layer, Network Layer, and Transport Layer are applied between the DOCSIS modem and CMTS.
In the RF return path, what adjusts the carrier amplitude from the channel source to correct for unequal path attenuation between the source and the first return amplifier (or node)?
(answer) Long loop automatic gain control (AGC).
If a return path impairment appears to be caused by impulse noise, why is it a good idea to begin troubleshooting at distribution taps of 17 dB or lower?
(answer) Low value taps have less isolation between ports and offer less attenuation to ingress and impulse noise coming from an individual drop system.
What are the units that can be used to represent signal level values?
(answer) Millivolt (mV), decibel millivolt (dBmV), and microwatt (µW) or nanowatt (nW).
If a leak is at an amplifier location, which antenna would be best for more precise determination of the exact source?
(answer) Near field probe.
What recourse do broadband cable operators have if citizens band (CB) and ham radio signals ingress into their network?
(answer) None, as long as the radio transmissions are at or below legal power levels, it is the cable operator's obligation to prevent these signals from entering their network.
What should be done when the location of electrical interference in the power network is identified?
(answer) Notify the power company with the exact location so the cause of the interference can be repaired.
What are two features that were added in Data Over Cable Service Interface Specification (DOCSIS) 3.1 to extend the viability of hybrid fiber/coax (HFC) networks into the next decade?
(answer) Orthogonal frequency division multiplexing (OFDM) and low-density parity-check (LDPC).
What features were introduced with the 3.1 version of the Data Over Cable Service Interface Specification (DOCSIS 3.1) to increase the downstream and upstream data throughput?
(answer) Orthogonal frequency division multiplexing (OFDM) and low-density parity-check (LDPC).
What feature of DOCSIS proactive network maintenance (PNM) can save the technician hours of troubleshooting?
(answer) PNM peforms correlation of data from all the modems in an area to pinpoint where the likely problem in the network can be found.
What did the 1.1 version of the Data over cable service interface specification (DOCSIS) introduce, incorporating solutions for transporting real-time data applications (such as voice traffic) over the cable operator's managed IP network, and doing so with quality comparable to that of the telephone company?
(answer) Packet cable
The line extender amplifier housing has
(answer) Plug-in connectors that direct the incoming forward RF signals from the input port to the RF amplifier module and the outgoing amplified signals from the amplifier module to the output port.
What practice can uncover potential return path problems in the drop system that can be mitigated before entering the network?
(answer) Prescreening the drop system for ingress or egress.
DOCSIS 1.1 added Service Flow to its media access control (MAC) protocol to
(answer) Provide a mechanism for upstream and downstream quality of service management.
Which type of digital modulation contains four symbols with 2 bits in each symbol?
(answer) Quadrature phase shift keying (QPSK).
What was added to the first Data Over Cable Service Interface Specification (DOCSIS) that enabled broadband cable operators to provide telephone service with quality and reliability that rivaled the products of the traditional telephone companies?
(answer) Quality of service (QoS) controls, enhanced security, and adaptive equalization in the upstream path.
Why are RF return channel carriers unusable for aligning return path equipment?
(answer) RF return channel carriers are of short duration and from multiple sources.
Why is it imperative to keep all ingress and impulse noise, even that outside the frequency range of the RF return carriers, to a minimum?
(answer) Regardless of the frequency, if the impulse noise or ingress is high enough, it can cause laser clipping.
The line extender amplifier
(answer) Requires the AC input voltage typically to be received through the port seizure screw connection.
What enables set-top boxes (STB) and Data over cable service interface specification (DOCSIS) modems to operate as completely separate systems that operate independent of each other?
(answer) STB and DOCSIS modem are assigned different upstream channels with dedicated receivers in the headend.
What is one limitation of Fabry-Perot (FP) lasers that is eliminated in distributed feedback (DFB) lasers?
(answer) Side modes.
When adjusting amplifier controls, remember that
(answer) Signal level controls compensate for slight variations in the input signal level caused by temperature changes and by signal loss from coaxial cable and passive devices.
Which technology will carry a signal the greatest distance without a repeater?
(answer) Single-mode.
What amplitude level should the output of return amplifiers be adjusted?
(answer) So that the amplifier gain is equal to the path attenuation that follows the amplifier.
What is it necessary in the optical return path to get the most performance from the DOCSIS 3.1 specification?
(answer) Some combination of higher transmit power, more sensitive receivers, and lower path loss.
Which step in the troubleshooting process requires a discussion with the customer to gather more detail about the problem?
(answer) Step 1: Identify the problem.
A directional coupler
(answer) Tap port leg can supply signal to a multiple dwelling unit (MDU) or a smaller number of customers while maintaining the maximum amount of signal on the original cable.
Signal attenuation between two individual customer tap ports at a specific frequency, with all other ports terminated, is the definition of
(answer) Tap-to-tap isolation.
What is the primary difference between coaxial express cable and coaxial distribution cable in an HFC architecture?
(answer) Taps are installed on coaxial distribution cable and not on express cable.
The term "bel" originated with the early days of
(answer) Telephone.
When looking at a cable modem's PreEqualization Tap response, what do you know if the ninth bar is less than 10 dB below the eighth bar?
(answer) That there are high micro-reflections and that the cause is near the modem, likely in the drop system.
One-tenth bel or 1 DB ratio.
(answer) The 10th root of the 1 bel ratio.
Which optical band is used for optical amplifiers due to the attenuation loss and availability of economical optical amplifiers?
(answer) The C band.
When comparing different sizes of?directional couplers with identical input signal levels,
(answer) The DC-12âs resulting tap port signal voltage levels are lower and output port signal voltage levels are higher than the respective port output levels for DC-7.
Which Data Over Cable Service Interface Specification (DOCSIS) layer is used by the cable modem termination system (CMTS) to differentiate between cable modems?
(answer) The DOCSIS Media Access Control (MAC) Layer.
Why is installing high-pass filters (HPF) at the tap on drops without two-way services considered a short-term solution to ingress and impulse noise migrating into the hybrid fiber/coax (HFC) network?
(answer) The HPF will have to be removed when cable modems and digital set-top boxes (STB) are activated at the addresses that have an HPF installed.
The first version of the Data Over Cable Service Interface Specification (DOCSIS) was approved as an international standard by what organization?
(answer) The International Telecommunication Union (ITU).
What spectrum analyzer function is particularly useful as it captures and holds ingress, impulse noise, and other impairments on its display so that they can be viewed and analyzed?
(answer) The Max Hold function.
Which Open Systems Interconnection (OSI) reference model layers does the MAC Layer in the Data Over Cable Service Interface Specification (DOCSIS) overlap?
(answer) The Physical and Data Link Layers.
What does the spectrum analyzer Zero Span function do?
(answer) The Zero Span function stops the analyzer's sweep and parks its tuner to a specific frequency, displaying amplitude vs. time
When all other factors are equal, if the bonding wire and the cable connecting the drop cable to consumer electronics are the same size, which should be shorter in order to correctly bond the installation?
(answer) The bonding wire.
What is reported when the signal level meter (SLM) in a return path alignment system displays the return test carriers as a delta measurement?
(answer) The calculated difference between the configured input and the received input.
What type of measurement removes any errors attributable to bandwidth and provides an "apples-to-apples" comparison between carriers of differing bandwidths?
(answer) The constant power per hertz
What happens to the data throughput when transitioning from quadrature phase shift keying (QPSK) to 16-QAM (quadrature amplitude modulation) in a channel of the same bandwidth?
(answer) The data throughput doubles.
In the forward signal path of the line extender,
(answer) The first equalizer is where the frequency-dependent attenuation (tilt) caused by the coaxial cable between the line extender and the previous upstream amplifier is corrected.
What information can be gathered by a return path monitoring system that captures the quadrature amplitude modulation (QAM) return channel from a DOCSIS modem?
(answer) The group delay, in-band ripple/tilt, and micro-reflections on the QAM channel.
Why is the broadband cable industry developing its own passive optical network (PON) standard instead of using standards already developed by the International Telecommunication Union (ITU) and the Institute of Electrical and Electronics Engineers (IEEE)?
(answer) The industry has invested a lot of money in HFC networks, Data Over Cable Service Interface Specification (DOCISIS), and other systems and devices that are still currently being used, but they are not compatible with ITU and IEEE PON standards.
What enables the set-top boxes (STB) upstream carrier to be located below 20 MHz and still be reliably received?
(answer) The narrow bandwidth and quadrature phase shift keying (QPSK) modulation.
What was done in Data Over Cable Service Interface Specification (DOCSIS) 3.0 to allow enough bandwidth for upstream carriers from previous DOCSIS versions?
(answer) The option to increase the top frequency of the upstream to 85 MHz.
You are doing an aerial installation of fiber-optic cable. When you survey the installation path, you see that the path runs near several short outbuildings and over a series of hedges. Which installation method should you use?
(answer) The pull-in method.
In a traditional analog return, the optical detectors are responsive to the power of the received signal. How does the signal level at the output of the upstream receiver relate to changes to its input power?
(answer) The signal level at the output of the upstream receiver changes 2 dB for every 1 dB change of received optical power level.
Operational gain is
(answer) The signal level difference between the input signal and the output signal.
When analyzing a problem, what can the technician learn by asking the customer to show or demonstrate the problem?
(answer) The symptoms of the problem can be viewed and any unusual screens or customer entries can be identified.
Three components of the tap housing (and not the tap faceplate) are
(answer) The threaded mounting tap, seizure screw mechanisms, and right-angled input and output ports.
The "bypass AC current capacity" is
(answer) The total AC current the line extender amplifier can pass through to other active devices.
Why is 38 MHz typically the highest frequency in the sub-band frequency that is used for upstream modem transmissions?
(answer) The upper edge of the sub-band frequency spectrum is prone to group delay caused by the diplex filters.
What should be checked if a large percentage of set-top boxes (STB) transmit above 55 dBmV, the upper end of the STB transmission level range?
(answer) The value of the attenuator pad at the input of the STB demodulator.
Why is the E band undefined for fiber-optics communications?
(answer) There is a lot of older fiber-cable still in use that may have unacceptable water-peak attenuation.
Why would a three-way unbalanced splitter be used in a system design?
(answer) There is a need for one of the three output ports to have a lower insertion loss than the other two ports.
Why are 6 MHz and 41 MHz good choices for test carriers when injecting test carriers into a return path spectrum of 5 MHz to 42 MHz?
(answer) These frequencies are at the edges of the return frequency spectrum and are available.
What should be done about injected test carriers at the node appearing at the transceiver in the headend with frequency response variations of less than 1 dB?
(answer) These variations are normal and can usually be disregarded.
What is a characteristic of orthogonal frequency division multiplexing (OFDM) channel subcarriers?
(answer) They can be modulated at the maximum order of modulation for a given bandwidth that is suitable for the condition of the network.
When closing any distribution amplifier housing,
(answer) Tighten the bolts to the recommended torque in the proper tightening sequence, using an appropriate torque wrench.
What access technology does the first version of the Data Over Cable Service Interface Specification (DOCSIS 1.0) use to send data upstream over the network's RF return path?
(answer) Time division multiple access (TDMA).
In the traditional analog return path, what is critical about the upstream optical transmitter?
(answer) To make sure the RF level into the upstream transmitter is correct.
What is the best explanation of the function cladding performs in a fiber optic cable?
(answer) To reflect light as it passes through a cable.
What purpose do diplex filters fulfill when installed at the input and output of a two-way amplifier module?
(answer) To route the forward and return signals over different circuit paths to the appropriate section so that they can be amplified separately.
It is important to follow safety procedures when installing and handling fiber-optic cable. What should you use to pick up fiber pieces after you splice a cable?
(answer) Tweezers.
In the term 10BaseT what does the T mean?
(answer) Twisted pair.
Values expressed in dBmV that are preceded by a minus sign (-) represent
(answer) Values of voltage less than 1 millivolt (mV) across 75 ohms.
Which of the following is the distance occupied by 1 hertz (Hz)?
(answer) Wavelength.
Which of the following is used to define the waveform of an optical signal?
(answer) Wavelength.
29db
(answer) What is the maximum tap value that can be installed when the tap is connected directly to a line extender amplifier output and: (1) the line extender output is 45 dBmV @ 745.25 MHz; (2) the longest amount of Series 6 coaxial cable from the tap to either of the two TV sets is 150 feet; (3) the Series 6 coaxial cable attenuation rate is 5.65 dB/100 feet @ 750 MHz; (4) the drop includes a splitter with a 4.0 dB loss; and (5) the system minimum signal level required at each of the two TV sets is 3.0 dBmV?
When is the return path considered to be properly balanced with unity gain?
(answer) When the test carriers injected into the last amplifier in the cascade reach the transceiver in the headend with the same level as from the node.
Poor performance in the fiber-optic network leads you to believe that there is a fault in the fiber-optic cable and you want to test a section of the network with an optical time domain reflectometer (OTDR). How should you connect the OTDR to the fiber-optic cable?
(answer) With an optical mechanical splice.
Tap loss is
(answer)The signal attenuation between the input port and each tap port at a specific frequency.
