D3 End Lesson Qs
3.4 How else can a capacitance of 243 nanofarads (nF) be expressed?
0.243 microfarads
1.7 What is the total direct current (DC) loop resistance of a 350-foot piece of Series 59 drop cable when the DC loop resistance of that Series 59 cable is 56.04 ohms per 1,000 feet?
19.614 ohms
4.9 What type of filter is used in channel to traps to block some frequencies from arriving at the customer premises?
Band-stop filters
6.9 What is a priority in any standby power supply maintenance program?
Battery care
3.2 Which element likely has distributed capacitance?
Coaxial cable
1.2 Which of the following best describes current?
Excessive flow for a specific conductor size can cause the conductor to become too hot and melt or burn the conductor's insulating cover
1.4 How can an installer control the resistance of the drop cable being installed at a customer's premises?
Replace Series 59 with Series 6 cable because the Series 6 cable center conductor is larger in diameter, with lower resistance than Series 59 cable
1.8 Which term best describes the opposition a material or device offers to the current flow?
Resistance
9.4 Even though the downstream sweep test pulses are intended to fit in the narrow frequency band between channels, what parameter can cause interference if set too high?
Sweep test pulse amplitude
6.6 What inserts AC into the network with a direct connection to an amplifier rather than using a power inserter?
The amplifier AC circuitry
9.8 When standing waves are displayed in the sweep response, what does the frequency separation between response peaks indicate?
The approximate distance from the test point to the fault
3.5 What happens when you apply the direct current (DC) voltage of a battery to the conductive plates of a capacitor?
The plate connected to the positive battery terminal becomes positively charged as electrons, attracted by the positive voltage, flow from the plate
5.1 What is inductance?
The property by which voltage and current is induced into a circuit by a changing magnetic field
8.10 when configuring the upstream return in a distribution amplifier with multiple upstream ports, the amplitude levels for which port should be adjusted first?
the distribution amplifier upstream port with the most attenuation in its upstream path
8.5 how is the AC voltage separated from the RF signal in a distribution amplifier?
*** By a capacitor that passes RF but blocks the low frequency 60 Hz AC voltage which finds a low resistance path through the RF choke that blocks RF
8.6 what is the expected DC voltage on most HFC network equipment?
+ 24 VDC, +/- 0.5V
1.9 How many ohms is the amount of resistance that allows 1 ampere of current to flow when 1 volt of electromotive force is applied to a circuit?
1
2.3 To transport electric power efficiently, what power line voltage-current combination would deliver the same amount of power as 10 amps and 10,000 voluts, but with the least conductor loss?
2 amperes and 50,000 volts
1.3 What is the total DC loop resistance of a 1,850-foot piece of 0.500-inch coaxial cable with a DC loop resistance of 1.34 ohms per 1,000 feet?
2.479 ohms
9.2 Across 6 MHz, what is the maximum in-channel frequency response (ICFR) defined in the Data Over Cable Service Interface Specification (DOCSIS)?
3.0 dB P/V
2.4 Which sine wave frequency has the shortest wavelength?
750 MHz
6.10 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 AC source is a 90 VAC network power supply?
83.79 VAC
7.2 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 (to protect the distribution amplifier)?
A fast transfer electric crowbar (FTEC)
9.7 What could cause low-frequency roll-off of the downstream spectrum discovered when sweeping an amplifier?
A loose seizure screw in the downstream path
3.10 Which type of capacitor is likely used in a low frequency alternating current (AC) circuit where the maximum breakdown voltage is from 200 volts to 1,600 volts?
A paper capacitor
3.9 Which type of capacitor is constructed like a paper capacitor but with a different dielectric, and is available with either axial or radial leads?
A plastic-film capacitor
2.1 What forces AC to flow through a circuit?
A polarity changing voltage
2.10 What form of fluctuating DC is a symptom of a malfunctioning DC power supply in HFC amplifiers and fiber nodes?
AC ripple
6.7 What is the advantage for supplying AC to multiple amplifiers from one network power supply?
Allows the designer to place amplifiers without concern about access to electrical utility power
5.2 What is generated when the magnetic field around an inductor collapses?
An opposing voltage called cemf that is proportional to the rate of the changing current
10.4 Which type of applications are EVM expressions best suited?
Applications that have small random noise-like errors
3.6 What is 1 time constant (1 T) of a capacitor?
Approximately 63% of the source voltage, the product of the circuit resistance (R) and the capacitance (C) of the capacitor (R x C)
9.9 What do normalized reference traces taken at a fiber-node test point establish?
Baseline sweep responses that are used to balance and sweep all the amplifiers serviced by that fiber-node
4.5 Why is the circuit impedance dependent on the AC frequency?
Because the capacitive and inductive reactance vary with the AC frequency
7.5 What is the purpose for distribution amplifiers in an HFC network?
Boost the downstream signals before being divided and circulated throughout neighborhoods in the coaxial cable portion of the network
6.2 How does surge protection at the input and output of a ferroresonant power supply defend against voltage surges?
By passing voltage surges (within the surge device rating) to ground without damage
3.3 What is the ratio of the charge transferred between the capacitor plates to the potential difference between the plates?
Capacitance
3.7 Why is the total capacitive reactance of a network of capacitors connected in parallel calculated by adding their reactance together like a series of resistors?
Capacitors in parallel act like one large capacitor whose plate area is equal to the sum of the conductive plate areas of the individual capacitors
6.8 Where is a clamp-on ammeter attached to measure the output current from a network power supply?
Clamped around the conductor attached to the leg that tightens down on the coaxial cable connector pin
10.9 What does a hole in the center of a QAM constellation symbol error cloud indicate?
Coherent interference from ingress, or a beat from another channel modulator, landing inside the QAM channel
7.10 Where does a distribution amplifier module receive the direct current (DC) required for operation?
From a DC power supply module that converts the alternating current AC voltage to DC voltage
4.10 What property of a filter with inductors (L) and capacitors (C) can stretch and distort digital TV data pulses, making it difficult for the receiver to recover the signal?
Group delay
10.3 What does the MER measurement of a QAM channel tell a technician?
How close the QAM channel is to the cliff where the number of bit errors exceeds the FEC capacity of the receiver and reception stops
10.5 In an adaptive equalizer display, what do the vertical bars to the right of the incident signal, the eighth bar from the right, represent?
How much equalization is being applied to the channel
9.6 How must a directional test point be installed in an amplifier to enable insertion of upstream sweep pulses and view the downstream sweep?
In a path common to the downstream and upstream
4.2 What is the cemf reaction that opposes a change in current flow through an inductor is called?
Inductive reactance
5.5 What is the opposition to AC above the resistance of the inductor to DC called?
Inductive reactance
10.1 Why do digital modulation channels have measurable analog parameters?
It is based on modulating an analog RF carrier with digital data
1.5 Which of the following best describes total resistance in a circuit?
It is the sum of the individual resistances in the circuit
7.6 What does a thermal control circuit in a distribution amplifier do?
It maintains the amplifier output levels as the input levels vary with temperature changes
1.6 What happens when the cross-sectional area of a conductor doubles?
Its resistance decreases to half its original value
1.1 Which of the following best describes load resistance?
Load resistance is the total resistance when the source and wire resistances are very small
5.10 What characteristic of ferrite allows its use as core material in RF applications?
Low electrical conductivity for less internal power loss at RF than other iron-core transformers
10.6 When checking the ICFR of a QAM channel in the customer premises, a frequency response with a repetitive ripple is a symbol of what?
Micro-reflections
4.8 What does a filter with enhanced flatness across the top, and sharpness at the edge of the bandwidth passed by the filter contain?
Multiple resonant circuits
5.4 What is the induction of emf into an inductor from the changing magnetic field lines around another inductor that encircle, or link, the turns of the inductors called?
Mutual inductance
5.8 What enables a transformer to transfer electrical energy from circuit to another
Mutual inductance
9.1 In modern sweep systems, what type of nonintrusive and noninterfering test signal is inserted into the downstream?
Narrow-band CW test carriers, called pulses, at frequencies between channels
6.1 What advantage is realized by increasing the voltage in a broadband cable network from 60 VAC to 90 volts?
Operating with 50% more voltage reduces the voltage drop and current drawn in the network for more efficient power utilization
2.8 What is defined as the most positive or most negative point of each sine wave half cycle?
Peak value
9.5 What does a normalized reference trace from a fiber-node test point eliminate from the sweep process?
Slope and response variations of the headend and optical transport
1.10 What does current flow encounter within a power source when traveling from the positive terminal to the negative terminal?
Source resistance
4.6 What is the bandwidth of a resonant circuit?
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
6.4 In a standby network power supply, what comes online to convert the battery voltage to AC, which then goes to the ferroresonant transformer?
The battery-powered inverter
4.1 What happens when AC is applied to an inductor?
The changing polarity AC source current is continually opposed by the inductor cemf current
5.9 For the power in the primary and secondary windings of a transformer to remain equal, what must the current in the secondary windings do when the voltage is stepped up?
The current in the secondary windings must step down in proportion to the voltage increase
2.6 What is the sine wave phase angle?
The distance in degrees from the 0 degree reference point to any other point on the waveform
9.3 When sweeping the upstream return path in a HFC network, where are the upstream levels and sweep responses measured?
The headend
5.3 What units are used to express inductance?
The henry (H)
5.6 What is the relationship of the inductive reactance of an inductor and frequency?
The higher the frequency, the higher the inductive reactance
7.1 When opening a distribution amplifier station housing, why is it usually unnecessary to loosen the bolts at the bottom of the housing?
The housing lid is usually attached to the base of the housing with hinges
6.3 Which part of the ferroresonant transformer regulates the load on the secondary winding?
The magnetic shunt
2.7 What is the peak value of a sine wave?
The most positive or most negative level of each sine wave half cycle
4.7 In a resonant circuit, what property is adjusted to achieve the desired bandwidth?
The quality factor (Q)
2.9 What is a characteristic of the quasi-square wave produced by the ferroresonant transformer in HFC network power supplies?
The quasi-square wave edges become more rounded as the load increases
5.7 When a circuit has several inductors, how is the total inductive reactance calculated?
The same way the total resistance of resistors in a circuit is determined
10.7 Why does the information in STB and modem diagnostic screens often appear cryptic to a customer?
The screens use initials, acronyms, and jargon intended for people that are familiar with the product
2.5 What defines the period of a sine wave?
The time that it takes for completion of one cycle of the signal
10.8 What enables assessment of upstream DOCSIS channel parameters using the QAM analyzer function of a signal level meter (SLM)?
The upstream channels from the built-in DOCSIS modem are optimized for the upstream path and the channel parameters displayed by the instrument
3.8 What do you call the maximum voltage that a given capacitor can handle?
The working voltage
7.9 What characteristics about upstream signals from cable modems and set-top boxes (STB) make them impractical for verifying and aligning a distribution amplifier return section?
They are of short duration and originate from various locations
7.4 How does a distribution amplifier in a fiber node receive the downstream radio frequency (RF) signals?
Through a coaxial cable that is connected to the downstream optical receiver
2.2 How is the AC voltage from a generator accessed?
Through slip rings that maintain physical contact with stationary brushes that can be connected directly to a circuit
6.5 In a power inserter with three filtering networks, what is the purpose of the high-pass filter?
To prevent the 60 Hz AC from passing between the two RF/AC ports
9.10 Why is the main downstream output/upstream input port of a distribution amplifier typically the first to be swept in the downstream direction?
To select equalizers and set the output amplitude levels
7.7 Why is there a diplex filter at each downstream output port in a distribution amplifier?
To separate the downstream radio frequency (RF) from the upstream RF signals
10.10 When a test instrument indicates measurements that fall outside of minimum or maximum requirements, why should a technician recognize what the failed measurements are?
To troubleshoot and resolve the cause of failed measurements
7.3 What is the basic amplifier application that increases the amplitude of the radio frequency (RF) signal to compensate for the signal loss of cable and passive devices preceding the amplifier called?
Unity gain
3.1 How do you obtain the simplest form of capacitance?
Using two parallel metal plates separated by an insulator
10.2 Which characterizes a QAM channel?
When of equal amplitude and bandwidth, the power level of a QAM channel is several dB higher than an analog TV channel
4.3 Why does it appear that a capacitor passes AC, but blocks DC?
With an AC source, the capacitor continually charges and discharges for current flow in the same direction, appearing to pass through the capacitor
4.4 How does capacitive reactance oppose a changing applied voltage?
With energy that is temporarily stored in an electric field
8.3 What is installed in the input stage of a distribution amplifier for a flat frequency response into the input amplifier when the input signal has negative tilt?
a cable equalizer with positive slope
8.7 What term describes the frequency spectrum into an amplifier having higher amplitude at low frequencies than the high frequencies?
negative tilt
7.8 What is used to select which distribution amplifier secondary downstream output ports are active and whether they have equal or unequal output levels?
plug-in modules or jumpers
8.9 what value of interstage equalizer should be installed if the associated amplifier tombstone field is blank and the amplifier output slope is 7 dB
the default factory value
8.8 when configuring the input stage of a distribution amplifier, what element values can vary from those in the amplifier tombstone, depending on the input amplitude measurements?
the input equalizer and attenuator pad values
8.4 why is the term "gain control" applied to amplifier gain and controls inaccurate?
the only way to vary the output of any amplifier is to adjust the amplitude level of the signal going into the amplifier
8.1 Describe an application for a distribution amplifier in an HFC network?
to maintain downstream amplitude levels to addresses farthest from the fiber-node
8.2 In a distribution amplifier, why is the frequency response at the input of the second output stage sloped?
to reduce intermodulation distortion levels caused by amplifying high amplitude input levels
