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Service Technician exam Revised
Questions and Answers / Sure A +
Which of the following is the distance occupied by 1 hertz (Hz)? - ✔✔Wavelength What is the return signal pass band frequency used in most of North America? - ✔✔ 5 - 42 MHz What is the primary difference between coaxial express cable and coaxial distribution cable in an HFC architecture? - ✔✔Taps are installed on coaxial distribution cable and not on express cable. Which testing device is the best to use to measure cable faults? - ✔✔A time domain reflectometer (TDR). Which of the following is used to define the waveform of an optical signal? - ✔✔Wavelength. What is the function of an interdiction unit? - ✔✔An interdiction unit controls the level of service to the drop ports it contains. Which of the following devices is an active device? - ✔✔An addressable tap. The impedance of coaxial cable or a device is made up of the combined effects of which three electrical properties - ✔✔Resistance, inductance, and capacitance. 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? - ✔✔The bonding Wire Why would a three-way unbalanced splitter be used in a system design? - ✔✔There is a need for one of the three output ports to have a lower insertion loss than the other two ports. Alternating current is a current - ✔✔That changes direction (or alternates) in the conductor each time the potential difference applied to the ends of the conductor changes (or alternates) its polarity.
A simple AC generator containing a wire loop rotating between the poles of a magnet produces AC voltage - ✔✔Through magnetism and mechanical motion Through magnetism and mechanical motion. - ✔✔Is directly proportional to the amount of resistance present and to the square of the amount of current. To transmit AC power efficiently, what power line voltage-current combination would deliver the same amount of power as 10 amps and 10,000 volts, but with the least heat loss? - ✔✔2 amps and 50,000 volts. In a power transmission circuit, the transformer located near the user's home, Typically - ✔✔Converts the high voltage, low current combination carried on the transmission lines to a low voltage, high current combination for residential use. All true AC waveforms - ✔✔Always are symmetrical about the horizontal axis. The output voltage waveform generated by an AC generator during one complete rotation of the generator's armature - ✔✔Is called a sine wave. The square wave and the sawtooth wave AC waveforms - ✔✔Seem to decrease "instantly" from a maximum positive value to a maximum negative value of voltage or current. The polarity of a DC waveform - ✔✔Does not change. A fluctuating DC waveform - ✔✔Can be identical to an AC waveform, except that the fluctuating DC waveform never changes polarity. One cycle - ✔✔Is equal to one complete rotation of the armature of an AC generator. What is the wavelength of one cycle of an AC waveform when: (1) the frequency of the waveform is 80 Hz; (2) the speed of light is 300,000 kilometers per second; and (3) the waveform has an amplitude of 5 volts? - ✔✔3,
Eddy currents - ✔✔Can cause a loss of power in an AC circuit. The eddy-current losses in the conductors of an AC circuit are - ✔✔Dependent on the frequency of the current flowing through the conductors. Skin-effect losses - ✔✔Are reduced by using multiple-strand conductors instead of a single, large diameter conductor. What is the value of the current when: (1) the effective voltage is 120 volts; (2) the resistance of the source is 3 ohms; (3) the resistance of the conductors is 2 ohms; and (4) the resistance of the load is 5 ohms? - ✔✔12.00 amperes What is the power consumed by the load when: (1) the voltage across the load is 7.5 volts; (2) the current flowing through the circuit is 0.25 amperes; and (3) the resistance of the load is 30 ohms? - ✔✔1.88 watts What is the power consumed by coaxial cable loop resistance when: (1) the current of the coaxial cable circuit is 5 amperes; (2) the loop resistance of the coaxial cable is .9345 ohms; and (3) the AC power source has an effective voltage of 60 volts? - ✔✔23.36 Watts Induction - ✔✔Is the production of an electromotive force (emf) in a conductor by changes in the magnetic field around the conductor. A henry is - ✔✔Quite a large amount of inductance, so inductance in AC circuits is usually expressed as a smaller value; in fractions of one henry. Inductance is - ✔✔The property of an electrical circuit or conductor that tends to resist changes in the current flowing through the circuit or conductor. Inductance in an inductor - ✔✔Decreases when the number of turns around the core are decreased or when there is an increase in the spacing between the turns around the core. Inductors - ✔✔Are rated in units of henrys.
Mutual inductance is - ✔✔The property possessed by two inductors positioned so that the changing magnetic field lines around one of the inductors encircle, or link, the turns of the other inductor and induce an emf, or voltage, in that inductor. A transformer - ✔✔is either an air-core or an iron-core transformer. When the primary-to-secondary turns ratio in a transformer - ✔✔Is 1:2 or 1/2, the secondary coil voltage is two times larger than the primary coil voltage. Air-core transformers - ✔✔Get their name from the material used as the core of the transformer. The total inductance of an AC circuit - ✔✔Is equal to the sum of all the individual inductances when the circuit's inductors are connected in series. The total capacitance of individual capacitors - ✔✔Connected in series is always smaller than the smallest capacitor value. The capacitance of a capacitor is - ✔✔The ratio of the electric charge transferred from one plate to the other, to the potential difference between the plates caused by the applied voltage. What happens when a source of DC voltage is applied to the plates of a capacitor? - ✔✔The plate connected to the positive terminal of the source receives a positive charge. Capacitor charging - ✔✔Time is directly related to the size of the circuit resistance and the capacitance of the capacitor. Which of the following statements is true? - ✔✔When the capacitor plates have no charges on them, no electric field exists between the plates. A farad - ✔✔Is a unit of capacitance. One time constant (t) - ✔✔Equals the time required to charge a capacitor to 63% of its fully charged voltage.
Which of the following statements is true? - ✔✔The velocity of propagation is the rate that RF signals travel through the coaxial cable versus the speed that RF signals travel in free space. In abnormal coaxial cable attenuation changes, - ✔✔Trunk and feeder cable can also possess imperfections that cause random differences in attenuation at different frequencies. To connect a coaxial cable to a 750 MHz amplifier, use a - ✔✔Three-piece or two-piece pin connector. To connect two line passive or active devices together without jumper cables, use a(an) - ✔✔Housing-to-housing adapter. To properly prepare hardline coaxial cable for connectorization - ✔✔Some combination coring/stripping tools have an optional stop that automatically sets the coring/stripping depth for the proper center conductor length. When preparing armored cable for connectorization, a tubing cutter is used - ✔✔To cut all the way through the outer jacket and steel armoring so they can be removed using a knife and pliers. The polyethylene jacket on non-armored coaxial cable should be removed - ✔✔Using the correct jacket or non-armored coaxial cable should be removed Flooding compound should be cleaned from the cable - ✔✔Immediately after removing the jacket and/or armoring. Combination coring/stripping tools are used - ✔✔To core the dielectric while simultaneously stripping and beveling the aluminum sheath. After a foam dielectric cable is properly cored and stripped, the cable's center conductor should be - ✔✔Prepared with a pyramid-shaped cut to the tip. After wrench-tightening a two-piece pin connector's front nut to an amplifier, two adjustable wrenches are required because - ✔✔One wrench keeps the front nut from rotating while the other wrench tightens the back nut against the front nut.
To weatherproof a pin connector with heat shrink, the tubing - ✔✔Should be cut straight and clean if it needs to be trimmed, because jagged edges might split the tubing when it is heated. Which is inductive reactance? - ✔✔Equal to 2πƒL; π (pi) is 3.14, f is the frequency of the applied AC source voltage in hertz, and L is the circuit inductance in henrys. Which of the following describes counter electromotive force (cemf)? - ✔✔It determines the amount of current flowing through the circuit from the AC source, in an inductive AC circuit. What is the total inductive reactance of a circuit with three inductors in series when: (1) the inductors have individual inductances of 15 mh, 20 mh, and 25 mh; and (2) the AC power source is 50 Hz? - ✔✔18.84 ohms. Which statement about the total inductive reactance of a circuit with two inductors in parallel is true? - ✔✔It is always smaller than the lowest individual inductive reactance value among the inductors in the circuit. What happens when a capacitor is fully charged? - ✔✔The current reverses directions and flows back through the source. Which of the following is true about capacitive reactance? - ✔✔It is the opposition to current flow in an AC circuit caused by a capacitor. What is the total capacitive reactance of a circuit with two capacitors in series when: (1) the capacitors have individual capacitive reactances of 0.8 ohms and 1.6 ohms; (2) the AC power source is 1 MHz; and (3) the AC power source is 60 volts? - ✔✔2.40 ohms. Which of the following is true about the resonant frequency? - ✔✔It is the frequency at which the inductive reactance equals the capacitive reactance in a circuit with an inductor and a capacitor. Which of the following is true about the bandwidth of a resonant circuit? - ✔✔It is the band of frequencies between the 70.7% points of the voltage curve for parallel resonant circuits or the current curve for series resonant circuits.
What is the interfering RF signal level on output port 2 when: (1) the input leg is terminated; (2) the internal isolation is 32 dB; and (3) there is an applied signal of 7 dBmV on output port 2? - ✔✔- 25 dBmV A two-way splitter that is 600 feet away from an amplifier has what outputs when given the following: (1) the output of the amplifier is 25 dBmV at 50 MHz and 31 dBmV at 550 Mhz; (2) the 600 feet of cable loses 1.98 dB at 50 MHz and loses 6.48 dB at 550 MHhz; and (3) the two way splitter loses 3.8 dB at 50 MHz and loses 4.4 dB at 550 MHz? - ✔✔19.22 dBmV at 50 MHz and 20.12 dBmV at 550 MHz. What is the proper way to express a signal voltage of 10 mV in cable TV terms? - ✔✔20log(10mV/1mV) = 20 dBmV. What are two reasons why the output signal level from a directional coupler is less than the input signal level? - ✔✔The signal power sent to the tap port is not available to go to the output port, and the loss in the transformers and other parts of the directional coupler. Which of the following directional coupler values will exhibit the highest output insertion loss? - ✔✔7 dB Which statement characterizes a directional coupler? - ✔✔Which statement characterizes a directional coupler? What is the downstream output port signal level for a directional coupler when: (1) the input signal level is 35.0 dBmV; (2) the output port insertion loss value is 1.4 dB? - ✔✔33.6 dBmV. What does the configuration of the directional coupler faceplate and housing enable? - ✔✔The housing can be installed in any orientation, regardless of the direction of signal flow. Which of the following describes a power inserter? - ✔✔It contains a high-pass filter network that passes RF signals between the two RF/AC ports and blocks 60-Hz 60 VAC between the same two ports. Which of the following statements is true? - ✔✔For each power inserter, the system design must ensure that (1) the current required by any one RF/AC port does not exceed that ports power-passing
specification and the current required by both RF/AC ports does not exceed the AC input port power- passing specification 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 cable's 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? - ✔✔54. Calculate the capacitive reactance of a power inserter's feed-through capacitor when: (1) the frequency is 50 MHz; and (2) the capacitance value is 1,000 pF? - ✔✔5.30 Ohms. Which characterizes a feed-through tap? - ✔✔It has a directional coupler portion that efficiently routes most of the signal to the output port while removing a small amount of the signal and passing it to the splitter network. The terminating tap - ✔✔Is the last tap installed at the end of the feeder cable run. An RF/AC bypass tap - ✔✔Has the added feature of being able to maintain RF signal and AC voltage continuity during faceplate removal. Three components of the tap housing (and not the tap faceplate) are - ✔✔The threaded mounting tap, seizure screw mechanisms, and right-angled input and output ports. Tap loss is - ✔✔The signal attenuation between the input port and each tap port at a specific frequency. Signal attenuation between two individual customer tap ports at a specific frequency, with all other ports terminated, is the definition of - ✔✔Tap-to-tap isolation. Which of the following statements is true? - ✔✔In general, the closer the tap is to the amplifier output port the higher the tap value On cable system design maps, standard symbols include a - ✔✔Circle for a two-way tap, a square for a four-way tap, and a hexagon for an eight-way tap.
What is the state of the RF signals in a line extender when they are fed into the pre-amplifier? - ✔✔They are in a flat state. Reverse test alignment is used to adjust which of the following signal types? - ✔✔Test signals from the field to the headend. Unity gain is achieved when the signal strength along a cable is maintained at a specific level by the amplifiers. If the gain generated by an amplifier is too high, what will be the most likely result? - ✔✔Signal distortion. A distribution amplifier is housed in a die-cast aluminum housing. What is another item that can be mounted to the housing cover that connects to the distribution amplifier? - ✔✔DC power supply. A distribution amplifier requires a specific power input to function. How much DC power is provided by the B+ regulated DC voltage power supply? - ✔✔+24 volts DC. Shorts in the coaxial cable and excessive amounts of current can damage the distribution amplifier. Several devices can be used to protect the distribution amplifier from these problems. Which device shorts to ground when an overvoltage situation occurs? - ✔✔An FTEC (Fast Transfer Electronic Crowbar). There are several passive components in a distribution amplifier. Each component changes the signal in a different way. Which component reduces the signal equally at all frequencies? - ✔✔An attenuator pad. Which type of distribution amplifier gain control maintains the amplifier's RF output at a set level if the input levels to the amplifier change (within design tolerances)? - ✔✔An automatic gain control (AGC). Many factors influence signal attenuation. What is the effect of temperature on cable signal attenuation? - ✔✔The higher the temperature, the greater the cable signal attenuation. Which of the following distribution amplifier parts is controlled manually? - ✔✔The response control.
As you work with distribution amplifiers on the cable system, you must be aware that what you do can affect the various types of signal distortions. What type of distortion is defined as "an interfering beat whose frequency is ±.75 MHz or ±1.25 MHz from the video carrier frequency"? - ✔✔Composite second order (CSO). When you are installing or troubleshooting a distribution amplifier, what should you do to make sure that there is a flat frequency response coming from the amplifier? - ✔✔Make sure the cover plates are tightened. What does the output waveform of a ferroresonant transformer most closely resemble at maximum load? - ✔✔A sine wave. In a standby ferroresonant power supply, what device keeps the battery- powered AC power from feeding back to the utility? - ✔✔An isolation relay. Which tool do you use to accurately measure the output voltage of a ferroresonant power supply? - ✔✔A true RMS (root mean square) DMM. You are performing periodic maintenance on a standby ferroresonant power supply. Where should you measure the output current? - ✔✔At the stinger wire. There are three filtering networks in a power inserter. What is the purpose of the high-pass filter? - ✔✔To prevent the 60 VAC or 90 VAC from passing between the two RF/AC ports. In a ferroresonant transformer, what part regulates the load on the secondary winding? - ✔✔The transformer shunts. Which tool do you use to measure the input current on the input wiring? - ✔✔A clamp-on ammeter. What would be the voltage drop across a cable 1,250 feet away from a 60 VAC power supply, if the cable is .625-inch with a resistance of 1.1 ohm per 1,000 feet, conducting 4 amperes? - ✔✔5.5 VAC. What is the voltage into amplifier B, the second amplifier in cascade, under the following conditions? Each amplifier draws 1.5 amps of current. The output of
In a conventional axial leaded diode (one with a cylindrical body and leads coming out either end), the cathode is usually denoted by - ✔✔A band around the body of the diode. Which of the following was a popular circuit in the vacuum tube era? - ✔✔Center-tapped circuit. Which of the following statements is true of a forward-biased silicon diode? - ✔✔The voltage drop across the diode is approximately 0.7 volt. Schottky barrier diodes are popular as rectifiers because - ✔✔They have a lower voltage drop than do silicon diodes. One application for the varactor diode is - ✔✔As a reference frequency standard that locks 10 MHz oscillator to a precise frequency. The intrinsic region in the middle of a PIN diode is useful because - ✔✔It allows the RF resistance of the diode to be controlled by the DC current in the diode. If we have chosen our dopants correctly to generate light energy of the correct wavelength, what must be added to a light emitting diode to make it a Fabry Perot (F-P) laser? - ✔✔An interferometer, consisting of a mirror on one end of the laser diode and a partially- reflecting mirror on the other end. What is the purpose of a back-facet diode in an optical transmitter? - ✔✔To sense the light level being put out by the diode. If you needed to couple a control signal from one circuit to another, while keeping the ground connections isolated in the two circuits, what component would you use? - ✔✔Opto-isolator. What are two uses of PIN diodes? - ✔✔As current-variable RF resistors and fast RF switches. In use, a photodiode is normally - ✔✔Reverse biased. Modulation error ratio (MER) is an indicator of digital modulation signal quality. For error-free reception and adequate margin, what should be the minimum MER reading for a 256-QAM
(quadrature amplitude modulation) signal?Modulation error ratio (MER) is an indicator of digital modulation signal quality. For error-free reception and adequate margin, what should be the minimum MER reading for a 256-QAM (quadrature amplitude modulation) signal? - ✔✔32 dB. Bit error rate (BER) is one of the measurements a technician uses to determine how well the network is operating. What is an acceptable post-BER at the end of the drop? - ✔✔<1.0E-9. Coherent interference causes the constellation display to look like a series of small donuts. What is one cause of coherent interference? - ✔✔In-channel ingress. What information about the digital carrier can be learned by accessing the adaptive equalizer function of the digital signal analyzer? - ✔✔How much the adaptive equalizer has to compensate for linear distortions of the digital carrier When you use a digital signal analyzer to examine a digital signal, one of the values you should check is the symbol rate. What should the symbol rate setting be for a 256-QAM signal specified by the International Telecommunication Union (ITU) in ITU-T J.83 Annex B? - ✔✔5.360537 megasymbols per second (MS/s). Many cable operators have a drop certification program and require measurements using a digital signal analyzer with minimum and maximum criteria programmed into the instrument. Why should the technician recognize and understand which channels are being measured when automated measurements are being performed by the digital signal analyzer? - ✔✔To save measurement time, some cable operators perform automated measurements on a sample of channels which can result in problems going undetected in unmeasured channels. You have a cable modem analyzer and you want to replace the cable modem to determine whether the modem is bad. How should the modem analyzer be connected to replace the modem? - ✔✔An ethernet cable is connected from the cable modem analyzer to the customer's computer and the RF drop input cable is connected to the cable modem analyzer Why does it take a few minutes for a cable modem analyzer to become functional once connected to the network? - ✔✔Every time the cable modem analyzer function is enabled, the instrument's internal modem must be provisioned with the cable modem termination system (CMTS).
You want to check the blind spot of the coaxial cable for cable faults. Which of the following actions would be correct? - ✔✔Measure the cable from the opposite end. Certain ways of using a time domain reflectometer (TDR) are considered best practices, and are most likely to give you the most accurate results in the shortest amount of time. If you want to check a coaxial cable for faults and measure its length using the best practice, how would you set the pulse width? - ✔✔Start with the shortest pulse width. Which of the following is a requirement in the process for measuring leakage using a dipole antenna, as required by the FCC? - ✔✔The antenna must be placed 3 meters from the system components and 3 meters from the ground. Many cable companies require which type of leaks to be fixed? - ✔✔All types of leaks must be fixed. According to the FCC, the leakage log should contain which of the following? - ✔✔The probable cause of the leakage. Which of the following FCC required information must a cable system keep on file for two years? - ✔✔Annual CLI calculations, regular (quarterly) monitoring programs, and a list of all channels used in the aeronautical bands. If your leakage detector indicates there is a leak and displays a reading of 14 microvolts per meter (uV/m) when you are 80 feet from a possible leak source, what is the approximate calculated level of the leak from 10 feet? - ✔✔ 112 μV/m. If a large signal leak is found in the aerial plant, what is a good first step in locating the leak? - ✔✔Drive around until an absolute peak is found. Which of the following best describes demand maintenance procedures with regard to signal leakage? - ✔✔The demand maintenance procedures can improve the CLI measurement results by identifying and correcting the largest leaks first. When troubleshooting signal leakage in the drop system, what is indicated if all signs of signal leakage disappear when the ground block is disconnected and terminated on the side connected to the customer premises? - ✔✔The backward route from the ground block to the tap can be eliminated as a source of leakage.
Which typical over-the-air signal sources can cause a false alarm with a signal leakage detector? - ✔✔Typical sources include aircraft communication signals and ham, mobile, and government radio broadcasts. When adjusting or selecting the elements of a dipole antenna for measuring signal leakage, what is the approximate length of each element relative to the wavelength of the signal being measured? - ✔✔One-quarter wavelength. When light strikes a medium at an angle less than the critical angle, what happens to the light? - ✔✔It is reflected. In a fiber-optic cable, what is the purpose of the cladding? - ✔✔To guide light down the fiber. 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? - ✔✔1,550 nm. 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? - ✔✔Tweezers. 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? - ✔✔The pull-in method. 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? - ✔✔With an optical mechanical splice. 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? - ✔✔A refractive star coupler.
