system technician conventional
What is the expected DC voltage on most hybrid fiber соах (HFC) network equipment?
+24 VDC, + 0.5 V.
What is the thermal noise level used for reference in broadband cable noise calculations?
-59.2 dBmV.
When setting proactive network maintenance (PNM) severity metrics for main tap ratio (MTR), how much level change is typically worthy of attention?
3 dB
How many symbols are available at the output of a quadrature phase shift keying (QPSK) modulator
4 symbols, each containing 2 bits of data.
What is sent with digital TV (DTV) transmissions that enables the receiver to synchronize with the sending device to decode and place the data in the correct sequence?
A 27 MHz program clock reference (PCR).
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.
What is done to an operational amplifier (op amp) to create a low-pass filter circuit?
A capacitor is placed in parallel with the feedback resistor that is connected to the op amp inverting input (-).
What does "micro" in micro- reflections denote?
A close-in reflection whose time delay relative to the incident signal ranges from less than a symbol period to perhaps several symbol periods.
If only one modem indicated group delay issue in the return path, what would you suspect to be the culprit in the customer's drop system?
A high-pass filter, data-only filter, or a step attenuator.
What geometric shape is a sine wave based upon?
A right degree triangle
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 source
When included in an oscillator circuit, what component enables the oscillator frequency to be controlled by voltage, hence, the voltage controlled oscillator (VCO)?
A varactor (or varicap) diode.
What would be the likely cause of non-linear distortion in the broadband cable network?
An amplifier.
What information remains after the intermediate frequency (IF) signal is detected, or demodulated?
Analog or digital baseband information.
In addition to device and network parameters from DOCSIS modems, what information is needed to isolate the source of a problem in the network?
Analysis of the data along with network topology and device location.
Which must be done to create an oscillator if, the circuit transistor is in the common emitter configuration?
Another 180-degree phase shift is necessary for positive feedback.
What do nonlinear distortions of quadrature amplitude modulation (QAM) channels look like on a spectrum analyzer?
As noise-like bands without a defined signature
In a broadband cable network, where would a block convertor be most likely used?
At the node
What is the bias voltage setting of the transistors in a push-pull circuit configuration?
At the point that under quiescent (no-signal) conditions, the transistors are about to come on, conducting little if any collector (or emitter) current.
What property of a capacitor enables it to be used with an operational amplifier (op amp) to create a filter circuit?
At very low frequencies, capacitive reactance is high.
Why are micro-reflections some of the more difficult issues to diagnose?
Because they require physical inspection of the connectors and cable to find.
How is the AC voltage separated from the RF signal in a distribution amplifier?
By a capacitor that passes RF but ocks the low frequency 60 hertz (Hz) AC voltage which finds a low resistance path through the RF choke that blocks RF.
How is hysteresis added to an operational amplifier (op amp) comparator circuit to ensure the output is always either high or low?
By adding positive feedback from the op amp output to the non-inverting input.
When there is reflection indicated by an adaptive equalize, how do test instruments calculate the unknown distance to a reflection?
By dividing the time delay between the reflection and the incident signal by the cable velocity of propagation (VoP) per 100 feet.
How does feed-forward amplifier technology achieve distortion reduction that is better than power-doubling?
By introducing delay lines and error amplifiers.
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.
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.
In a radio receiver, what is almost universally used to conduct the energy between the antenna and the receiver tuner?
Coaxial cable
The direct current (DC) power supply modules in fiber-nodes and distribution amplifiers do what?
Convert the network alternating current (AC) voltage to DC o voltage used by the active devices within the weatherproof housing.
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 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).
What is used in set-top boxes (STB) to strike a balance between image rejection, the bandwidth of the intermediate frequency (IF) filter, and the frequency which modulation is done?
Double IF conversion
What logic family of bipolar transistor logic circuits is used extensively where the fastest speeds are required at the of expense power dissipation?
Emitter coupled logic (ECL)
What is another name for the bipolar junction transistor (BJT) common collector configuration? O Signal amplifier.
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
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 does the time-gated switch function on a spectrum analyzer enable?
In-service measurements of noise, beats, and ingress without disrupting service
What are harmonics from amplified quadrature amplitude modulation (QAM) channels generally called?
Intermodulation noise
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 type amplifiers are designed and intended to provide the final boosting of amplitude to the downstream signals exiting the headend?
Launch amplifiers.
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 of the op amp
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.
In which portion of a filter's frequency passband is group delay most likely to be encountered?
Near the filter's lower and upper frequency band edge.
What term describes the frequency spectrum into an amplifier having higher amplitude at low frequencies than the high frequencies?
Negative tilt.
Which of the following describes reactive maintenance?
Network activity initiated by metrics that show degraded service performance.
Calculating the signal voltage and current range on the output of a bipolar junction transistor (BJT) involve repeated applications of what?
Ohm's law.
What benefit does applying negative feedback in an amplifier circuit provide?
Operating stability.
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.
What is the bias voltage of a transistor without a signal present called?
Quiescent voltage.
Which resonant circuit mode of a crystal should be used in applications in which frequency accuracy is most important?
Series resonant
The detail of a displayed signal can be viewed and modified by adjusting the frequency range that the spectrum analyzer is sweeping via which setting?
Span
How would you find the input level to an amplifier if the specifications only give the amplifier output level at 1,002 MHz and the amplifier Operation Gain?
Subtract the amplifier Operation Gain from amplifier output level at 1,002 MHz.
What type of bandpass filters offer the precision, stability, and bandwidth most suitable for TV and set-top box (STB) intermediate frequency (IF) sections?
Surface acoustic wave (SAW) filters
What is the benefit of spectrum analyzers capable of automated measurements specifically for broadband cable networks?
Technicians with only basic instructions can obtain accurate measurements
Under what principle do frequency modulation (FM) detector circuit designs operate?
That voltage is created when the signal frequency moves from the center frequency.
What is the primary difference between the Hartley and Colpitts oscillator circuits?
The Colpitts oscillator uses capacitive feedback, and the Hartley uses inductive feedback.
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
What two significant signals go into the mixer to create the intermediate frequency (IF)
The RF signal frequency at the output of the front end filter and the local oscillator (LO) signal.
What are the peaks and minima of the amplitude modulation (AM) waveform envelope related to
The amplitude of the modulation signal.
Why is the isolation between the output and input sections of a common base transistor configuration quite high?
The base is typically at signal ground.
What is significant about how a crystal is cut with respect to the orientation of the quartz crystal lattice structure?
The cut dictates pretty much all crystal characteristics, including frequency drift with temperature.
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 port with the most attenuation in its upstream path
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 factory default value
Which stage in a hybrid fiber/coax (HFC) downstream amplifier maintains a uniform and high carrier-to-noise ratio (CNR) across the amplifier operating frequency spectrum with low nonlinear distortion levels?
The first, preamplifier, stage
What part of a receiver has several functions that include limiting the number of signals that reach the amplifier and mixer?
The front end filter.
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.
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 (+).
To maintain unity gain, what does the internal attenuation in an amplifier do when the temperature drops from 70° Fahrenheit (F) to 20° F?
The internal attenuation increases.
In a swept-tuned spectrum analyzer, which element gives the instrument its "swept-tuned" characteristic?
The internal sweep generator
Applying Carson's Rule to determine the bandwidth of a narrowband frequency modulation (FM) carrier, what is the most significant factor?
The maximum modulation signal frequency.
What do the number of filter poles generally correspond to?
The number of inductors plus capacitances that are in a filter circuit.
Why is the term "gain control" applied to amplifier gain and controls inaccurate?
The only way to very the output of any amplifier is to adjust the amplitude level of the signal going into the amplifier.
What risk is there in coupling the output of an oscillator to another circuit stage?
The oscillator frequency could be changed (or pulled by) the next circuit stage.
What prevents the subcarriers in orthogonal frequency division multiplexing (OFDM) from interfering with each other?
The peak power of each subcarrier aligns with the minimum power of the adjacent subcarrier.
In an operational amplifier (op amp), what is open-loop gain?
The pre-determined gain of the op amp without feedback
What is used to quantify the efficiency of an amplifier?
The ratio of how much direct current (DC) power is required for the useable power from the amplifier.
A micro-reflection signature consists of what pair of characterizing elements?
The relative level of the reflected signal compared to the main signal, and the delay of the reflected signal.
What do the cable modem termination system (CMTS) calculated adaptive equalizer coefficients received from the modems describe?
The residual linear channel distortion remaining after any pre-equalization.
What determines the voltage gain of an operational amplifier (op amp) inverter?
The value of the input and feedback resistors.
In a circuit with pure inductance, what is the phase relationship between the current and voltage?
The voltage leads the current by 90 degrees
Describe an application for a distribution amplifier in a hybrid fiber/coax (HFC) network?
To maintain downstream amplitude levels to the addresses furthest from the fiber node.
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 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
What benefit does a power- doubling configuration offer compared to a single cascade push-pull hybrid amplifier?
Twice the output with the same distortion.
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.
How should the gain of a broadband TV amplifier, such as a line extender, be calculated?
Using either power or voltage formulas.
Under what conditions is installation of a house amplifier appropriate?
When channel amplitude levels from the network are acceptable but too low for the number of outlets.
What is a characteristic of the monostable multivibrator?
When given a suitable input signal, it generates a single pulse of fixed length.
When is a temperature- controlled crystal oscillator (TCXO) likely to be used?
When techniques to compensate for crystal drift are inadequate for the application.
To meet design criteria for noise and distortion, where must amplifier input levels be kept?
Within the dynamic range of an amplifier, above the noise floor and below the saturation point.
What are the three elements of a carrier wave that can be manipulated
amplitude, frequency, phase
In a hybrid fiber/coax (HFC) network what type of crude amplitude modulation (AM) detector causes common path distortion (CPD)?
envelope detector
