Maintenance Tech I-II Conventional Questions and Answers 2023

What advantage is realized by increasing the voltage in a broadband cable network from 60 volts alternating current (VAC) to 90 volts? - Correct answer-Operating with 50% more voltage reduces the voltage drop and current drawn in the network for more efficient power utilization. How does surge protection at the input and output of a ferroresonant power supply defend against voltage surges? - Correct answer-By passing voltage surges (within the surge device rating) to ground without damage. Which part of a ferroresonant transformer regulates the load on the secondary winding? - Correct answer-The magnetic shunt. 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? - Correct answer-The battery-powered inverter. In a power inserter with three filtering networks, what is the purpose of the high-pass filter? - Correct answer-To prevent the 60 hertz (Hz) alternating current (AC) from passing between the two radio frequency (RF)/AC ports. What inserts alternating current (AC) into the network with a direct connection to an amplifier rather than using a power inserter? - Correct answer-The amplifier AC circuitry. What is the advantage for supplying alternating current (AC) to multiple amplifiers from one network power supply? - Correct answer-Allows the designer to place amplifiers without concern about access to electrical utility power. Where is a clamp-on ammeter attached to measure the output current from a network power supply? - Correct answer-Clamped around the conductor attached to the lug that tightens down on the coaxial cable connector pin. What is a priority in any standby power supply maintenance program? - Correct answerBattery care. What is the voltage into the second amplifier in cascade, if each amplifier draws 1.5 amps of current, the loop resistance of each section of cable is 1.38 ohms, and the alternating current (AC) source is a 90 volts AC (VAC) network power supply? - Correct answer-83.77 VAC. 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? - Correct answer-STB and DOCSIS modems are assigned different upstream channels with dedicated receivers in the headend. 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? - Correct answer-PacketCable. Why is 38 MHz typically the highest frequency in the sub-band frequency that is used for upstream modem transmissions? - Correct answer-The upper edge of the sub-band frequency spectrum is prone to group delay caused by the diplex filters. What enables the set-top box (STB) upstream carrier to be located below 20 MHz and still be reliably received? - Correct answer-The narrow bandwidth and quadrature phase shift keying (QPSK) modulation. What system is a byproduct of the "funneling effect"? - Correct answer-A many-to-one system. House amplifiers with a passive return path are used for what type of situation? - Correct answer-For situations when long service drops are used and the forward path needs to be amplified but return path amplification is unnecessary. Why does the output level from customer premises equipment (CPE) vary? - Correct answer-To compensate for variable amounts of attenuation in the return path of each device. 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? - Correct answer-3.5 dB. What purpose do diplex filters fulfill when installed at the input and output of a two-way amplifier module? - Correct answer-To route the forward and return signals over different circuit paths to the appropriate section so that they can be amplified separately. How does the signal attenuation through coaxial cable in the sub-band frequency spectrum compare to the attenuation at forward path frequencies? - Correct answer-At sub-band frequencies, the signal attenuation is significantly less than in the forward path. What recourse do broadband cable operators have if citizens band (CB) and ham radio signals ingress into their network? - Correct 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. How is impulse noise characterized when viewed on a spectrum analyzer? - Correct answer-Impulse noise will appear as random spikes of energy across the entire return path frequency spectrum (5 to 42 MHz). How can the amount of thermal noise added to a network be minimized? - Correct answer-By ensuring that the RF input is at or above the specified minimum input level to all amplifiers. What location in the network is common path distortion (CPD) most severe? - Correct answer-At the output of a forward amplifier because the forward levels are highest and the return levels are lowest. What distinguishes a micro-reflection from other types of signal reflections? - Correct 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 (µs). What are the symptoms of hum on an upstream digital modulation channel? - Correct answer-Bit errors occur, similar to impulse noise and ingress on the upstream path. 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? - Correct answer-Regardless of the frequency, if the impulse noise or ingress is high enough, it can cause laser clipping. 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? - Correct answer-That there are high micro-reflections and that the cause is near the modem, likely in the drop system. What practice can uncover potential return path problems in the drop system that can be mitigated before entering the network? - Correct answer-Prescreening the drop system for ingress or egress. 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? - Correct 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. What should be done before diagnosing a return path problem in the drop system? - Correct answer-Confirm that the hybrid fiber/coax (HFC) network is working properly. 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? - Correct answer-The Max Hold function. What should be done when the location of electrical interference in the power network is identified? - Correct answer-Notify the power company with the exact location so the cause of the interference can be repaired. What can be used with a signal level meter (SLM) to check the drop system for RF continuity at sub-band frequencies? - Correct answer-A signal generator. What information can be gathered by a return path monitoring system that captures the quadrature amplitude modulation (QAM) return channel from a DOCSIS modem? - Correct answer-The group delay, in-band ripple/tilt, and micro-reflections on the QAM channel. What feature of DOCSIS proactive network maintenance (PNM) can save the technician hours of troubleshooting? - Correct 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. When should a preamplifier be used to measure impairments with a spectrum analyzer? - Correct answer-If the noise floor drops less than 10 dB when the input signal is removed from the spectrum analyzer. What does the spectrum analyzer Zero Span function do? - Correct answer-The Zero Span function stops the analyzer's sweep and parks its tuner to a specific frequency, displaying amplitude vs. time How is laser clipping in the return path characterized on a spectrum analyzer? - Correct answer-By an elevated noise floor above 42 MHz after the optical signal has been converted back to RF, typically in the headend. 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? - Correct 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 amplitude level should the output of return amplifiers be adjusted? - Correct answer-So that the amplifier gain is equal to the path attenuation that follows the amplifier. 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? - Correct answer-The value of the attenuator pad at the input of the STB demodulator. What type of measurement removes any errors attributable to bandwidth and provides an "apples-to-apples" comparison between carriers of differing bandwidths? - Correct answer-The constant power per hertz (power/Hz) measurement. Why are RF return channel carriers unusable for aligning return path equipment? - Correct answer-RF return channel carriers are of short duration and from multiple sources. 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? - Correct answer-These frequencies are at the edges of the return frequency spectrum and are available. Where should the injected sweep pulses be placed to avoid interference with active return carriers when sweeping the return path? - Correct answer-Between active return carriers only if there is adequate space to accommodate the bandwidth of the injected sweep pulses What is reported when the signal level meter (SLM) in a return path alignment system displays the return test carriers as a delta measurement? - Correct answer-The calculated difference between the configured input and the received input. When is the return path considered to be properly balanced with unity gain? - Correct 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. 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? - Correct answer-These variations are normal and can usually be disregarded. The return path alignment system transceiver is specified to have 0 dBmV from 5 MHz to 42 MHz. With injected test carriers that are flat across the return spectrum and the input to a line extender at the correct level, what value equalizer and attenuator pad should be installed if the transceiver reports 3.2 dBmV at 6 MHz and 2.5 dBmV at 41 MHz? Equalizers come in 2 dB increments and attenuator pads in 1 dB increments? - Correct answer-A 0 dB equalizer, and 3 dB attenuator pad. Which type of digital modulation contains four symbols with 2 bits in each symbol? - Correct answer-Quadrature phase shift keying (QPSK). How many decimal values can eight bits of data represent? - Correct answer-256 What is a characteristic of orthogonal frequency division multiplexing (OFDM) channel subcarriers? - Correct answer-They can be modulated at the maximum order of modulation for a given bandwidth that is suitable for the condition of the network. What media access control (MAC) protocols are specified for digital set-top boxes (STB)? - Correct answer-ALOHA and time division multiple access (TDMA).