System Technician 1-13
what spectrum analyzer function can left on for extended periods of time to capture transient signals and ingress, including intermittent signals that can be difficult to identify?
Max hold.
what spectrum analyzer function can be used to capture consistent, low-amplitude level signals that interfere with the short-duration return path channels?
Min hold.
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 hertz (Hz) ac voltage which finds a low resistance path through the rf choke that blocks rf.
calculating the signal voltage and current range on the output of a bipolar junction transistor (BJT) involve repeated applications of what?
ohm's law
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 is the thermal noise level used for reference in broadband cable noise calculations ?
-59.2 dBmV.
In a radio receiver, what is universally used to conduct energy between the antenna and the receiver tuner?
Coaxial cable
in a swept-tuned spectrum analyzer, which element gives the instrument its "swept-tuned" characteristics ?
an internal sweep generator.
in a broadband cable network, where would a block convertor be most likely used ?
at the node.
which class of amplifier efficiency approaches, but never achieves, 100%
class D amplifier
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 frequency spectrum with low nonlinear distortion levels?
the first, preamplifier, stage.
When sweeping the upstream return path in a hybrid fiber coax (HFC) network, where are the upstream levels and sweep responses measured?
the headend.
what do the number of filter poles generally correspond to ?
the number of inductors plus capacitance that are in a filter circuit.
how is the spectrum analyzer video bandwidth (VBW) used ?
to reduce the noise displayed by the spectrum analyzer to view low amplitude signals more clearly without changing measurement results.
why is the main 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.
what benefit does a power-doubling configuration offer compared to a single cascade push-pull hybrid amplifier?
twice the output with the same distortion.
what is a characteristics of the monostable multivibrator ?
when given a suitable input signal, it generates a single pulse of fixed length.
what is done to an operational amplifier (OP AMP) to create a low-pass filter circuit?
a capacitor is placed 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 indicate a 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.
how is hysteresis added to an operational amplifier (OP AMP) comparator circuit to ensure the output is either high or low?
by adding positive feedback from the op amp output to the non-inverting input.
which class of amplifier has an output that is very high in harmonics and must be attenuated by a filter network
class C amplifier
what does the time-gated switch function on a spectrum analyzer enable ?
in-service measurement of noise, beats, and ingress without disrupting service.
in an operational amplifier (OP AMP), what is open-loop gain?
the pre-determined gain of the op-amp without feedback.
when is a temperature-controlled crystal oscillator (TCXO) likely to be used?
when techniques to compensate for crystal drift are inadequate for the application.
what is the expected dc voltage on most hybrid coax (HFC) network equipment?
+24 VDC, +0.5 V
when setting proactive network maintenance (PNM) severity metrics for main tap ratio(MTR), how much level change is typically worthy of attention?
3 db
across 6 megahertz, what is the maximum in-channel frequency response (ICFR) defined in the Data Over Cable Service Interference Specification?
3.0 db peak-to-valley (P/V).
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) is detected, or demodulated ?
Analog or digital baseband information
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 set-top boxes (STB) To strike a balance between image rejection, the bandwidth of the intermediate frequency(IF)filter, and the frequency at which demodulation is done?
Double IF conversion.
what characterizes N-doped silicone that is used in bipolar junction transistor (BJT)?
N-doped silicone has an excess free electrons compared to P-doped silicone
in modern sweep systems, what type of nonintrusive and noninterfering test signal is inserted into the downstream?
Narrow-band continuous wave (CW) test carriers, called pulses, at frequencies between channels.
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
the amplitude, or vertical deflection on the spectrum analyzer display is adjusted by what instrument settings?
The RF input attenuator and intermediate frequency (IF) gain.
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 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
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
describe an application for a distribution amplifier in a hybrid fiber/coax (HFC) network?
To convert downstream optical signals to an RF signal that can be distributed to a local neighborhood.
what is sent with digital TV (DTV) transmission's 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 could cause low-frequency roll-off of the downstream spectrum discovered when sweeping an amplifier ?
a loose seizure screw in the downstream path.
in a N-channel enhancement mode metal oxide semiconductor field effect transistor (MOSFET), what effectively turns the P substrate between the two wells into a induced N-channel?
a suitable positive voltage placed between the gate and the 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.
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 of energy without a defined signature.
what is the bias voltage setting of the transistors in a push-pull circuit configuration?
at the point 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
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.
Why are micro-reflections some of the more difficult issues to diagnose?
because they require physical inspection of the connectors and cable to find.
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 amplifiers utilizes a push-pull amplifier configuration in which each transistor conducts current during opposite cycles of the input signal.
class B amplifier
the direct current (DC) power supply modules in fiber-nodes and distribution amplifiers do what ?
convert the network alternating current (AC) to DC voltage used by the active devices within the weatherproof housing.
what is used in some receivers to remove all attenuation before the amplifier until the received signal level reaches a designated threshold?
delayed Automatic gain control (AGC).
what logic family of bipolar transistor logic circuits is used extensively where the fastest speeds are required at the expense of power dissipation ?
emitter coupled logic (ECL)
what is another name for the bipolar transistor(BJT) common collector configuration?
emitter follower
in what application would a bipolar transistor (BJT) common base configuration be used ?
for impedance isolation between a low-impedance device and high impedance amplifier
How must a directional test point be installed in an amplifier to enable insertion of upstream sweep pulses and view the downstream sweep?
in the path common to the downstream and upstream .
what are harmonics from amplified quadrature amplitude modulation (QAM) generally called ?
intermodulation noise.
How does complementary metal oxide semiconductor (CMOS) technology combat capacitance in a circuit ?
it combines the N-channel and p-channel metal oxide semiconductor field effect transistors (MOSFET) onto a signal substrate
what type of 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 to the op amp
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 a 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.
what benefit does applying negative feedback in an amplifier circuit provide?
operation stability.
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
what does a normalized reference trace from a fiber-node test point eliminant from the sweep process ?
slope and response variations of the headend and optical transport.
the detail of a displayed signal can be viewed and modified by adjusting the frequency range that the spectrum analyzer is sweeping via witch 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
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
what is the benefit of spectrum analyzer capable of automated measurements specifically for broadband cable networks?
technicians with only basic instruction can obtain accurate measurements.
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 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 upstream port with the most attenuation in its upstream path.
why is the isolation between the output and input sections of a common base transistor configuration quite high?
the input and output signals are in-phase with each other.
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 a 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 to 20 Fahrenheit ?
the internal attenuation increases.
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.
what is used to quantify the efficiency of an amplifier ?
the ratio of how much direct current (DC) power is required for the usable power from the amplifier.
a micro-reflection signature consist 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.
in combination with the sweep time, which spectrum analyzer setting determines how well signals will be defined and displayed on the spectrum analyzers screen?
the resolution bandwidth (RBW) setting.
which spectrum analyzer setting adjusts the amount of time the analyzer circuitry takes to sample the input signal or channel and then trace the amplitude and signature on the analyzer's display?
the sweep setting.
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.
why do metal oxide semiconductors field effect transistors (MOSFET) have internal zener diodes from the gate to the source or substrate ?
to prevent damage from static electricity
in a distrubtion amplifier, why is the frequency response at the input of the second output stage slopped?
to reduce intermodulation distortion levels caused by amplifying high amplitude input levels.
how should the gain of 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.
