NCTI MT1-MT2

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.

Where should the injected sweep pulses be placed to avoid interference with active return carriers when sweeping the return path?

Between active return carriers only if there is adequate space to accommodate the bandwidth of the injected sweep pulses.

What are the symptoms of hum on an upstream digital modulation channel?

Bit errors occur, similar to impulse noise and ingress on the upstream path.

How is laser clipping in the return path characterized on a spectrum analyzer?

By an elevated noise floor above 42 MHz after the optical signal has been converted back to RF typically in the headend.

How can the amount of thermal noise added to a network be minimized?

By ensuring that the RF input is at or above the specified minimum input level to all amplifiers..

What should be done before diagnosing a return path problem in the drop system?

Confirm that the hybrid fiber/coax (HFC) network is working properly.

In a DOCSIS 3.1 orthogonal frequency division multiple access (OFDMA) upstream channel, the average power of the subcarriers are normalized to what bandwidth?

1.6 MHz.

What is the maximum allowable signal detectable in the airspace during a flyover?

10 uv/m.

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 uV/m.

The code words and spreading algorithm of synchronous code division multiple access (S-CDMA) enable simultaneous transmission of up to how many modems on the same RF return channel?

128

How long must the leakage log be kept on file?

2 Years.

What is the voltage on the secondary of a transformer if the number of secondary windings is 25% of the primary windings?

25% of the voltage on the transformer's primary.

decimal values can eight bits How many of data represent?

256

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 peak-to-valley (P/N).

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?

3.5 dB.

CLI calculations do not include leakage below:

50 uv/m.

What cumulative leakage index (CLI) meets Federal Communications Commission (FCC) requirements?

64 or less

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 dB increments?

A O dB equalizer, and 3 dB attenuator pad. ( 3.2-2.5=.7)

Which type of rectifier circuit uses two alternating current (AC) waveforms on the transformer secondary?

A full-wave rectifier with a center-tapped transformer secondary.

What could cause low-frequency roll-off of the downstream spectrum discovered when sweeping an amplifier?

A loose seizure screw in the downstream path.

What system is a byproduct of the "funneling effect"?

A many-to-one system.

What can be used with a signal level meter (SLM) to check the drop system for RF continuity at sub-band frequencies?

A signal generator

What media access control (MAC) protocols are specified for digital set-top boxes (STB)?

ALOHA and time division multiple access (TDMA).

Which advanced Physical Layer (PHY) technology developed and added to DOCSIS 2.0 includes byte interleaving?

Advanced time division multiple access (A TDMA).

What access schemes were introduced with advanced Physical (PHY) Layer technologies in DOCSIS 2.0?

Advanced time division multiple access (A-TDMA) and synchronous code division multiple access (S CDMA).

Many cable companies require which type of leaks to be fixed?

All types of leaks must be fixed.

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.

How does the signal attenuation through coaxial cable in the sub-band frequency spectrum compare to the attenuation at forward path frequencies?

At sub-band frequencies, the signal attenuation is significantly less than in the forward path.

What location in the network is common path distortion (CPD) most severe?

At the output of a forward amplifier because the forward levels are highest and the return levels are lowest.

According to SCTE- and NCTA- recommended trunk system map symbols, fiber-optic cable is represented by

Double arrows within a small circle on a solid line.

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.

How is impulse noise characterized when viewed on a spectrum analyzer?

Impulse noise will appear as random spikes of energy across the entire return path frequency spectrum (5 to 42 MHz).

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.

When transmitting broadband signals

In a two way hybrid fiber/coax (HFC) network, two or more individual optical fibers are required for each optical node location.

What distinguishes a micro-reflection from other types of signal reflections?

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 few microseconds (us).

What term describes changes in output direct current (DC) voltage with changes in input alternating current (AC) voltage expressed as a percentage?

Input regulation.

Which of the following problem(s) are caused by egress?

Interference with aeronautieal navigation and communication, amateur radio public service, and cellular communications.

What does a normalized reference trace from a fiber-node test point eliminate from the sweep process?

Slope response variations of the Headend and optical transport.

What amplitude level should the output of return amplifiers be adjusted?

So that the amplifier gain is equal to the path attenuation that follows the amplifier.

In a basic step-up switcher circuit design, what does the inductor do when the switch is closed and conducting current to ground?

It stores energy in its magnetic field with the current lagging the voltage by 90 degrees.

A dipole antenna is used for FCC tests because:

Its performance is well characterized.

what leakage level must be entered in the leakage log?

Leaks 20 uv/m or higher measured 10 feet from the cable.

What are the disadvantages of using an SLM for leakage detection?

Less sensitive than a leakage detector and doesn't have an alarm.

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?

Low value taps have less isolation between ports and offer less attenuation to ingress and impulse noise coming from an individual drop system.

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 a frequencies between channels.

What recourse do broadband cable operators have if citizens band (CB) and ham radio signals ingress into their network?

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.

What should be done when the location of electrical interference in the power network is identified?

Notify the power company with the exact location so the cause of the interference can be repaired.

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.

What feature of DOCSIS proactive network maintenance (PNM) can save the technician hours of troubleshooting?

PNM peforms correlation of data from all the modems in an area to pinpoint where the likely problem in the network can be found.

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?

PacketCable.

What practice can uncover potential return path problems in the drop system that can be mitigated before entering the network?

Prescreening the drop system for ingress or egress.

In a HFC network,

Processing equipment in the headend converts the forward RF signal to a light signal.

Which type of digital modulation contains four symbols with 2 bits in each symbol?

Quadrature phase shift keying (QPSK),

Why are RF return channel carriers unusable for aligning return path equipment?

RF return channel carriers are of short duration and from multiple sources.

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.

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?

That there are high micro-reflections and that the cause is near the modem, likely in the drop system.

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?

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.

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 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?

The Max Hold function.

What does the spectrum analyzer Zero Span function do?

The Zero Span function stops the analyzer's sweep and parks its tuner to a specific frequency, displaying amplitude vs. time

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.

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.

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 The backward route from the ground block to the tap can be eliminated as source of leakage.

What is reported when the signal level meter (SLM) in a return path alignment system displays the return test carriers as a delta measurement?

The calculated difference between the configured Input and the received input.

What type of measurement removes any errors attributable to bandwidth and provides an "apples-to-apples" comparison between carriers of differing bandwidths?

The constant power per hertz (power/H2) measurement.

Which of the following is a repair order specification when measuring leakage levels?

The location of the leak.

What enables the set-top box (STB) upstream carrier to be located below 20 MHz and still be reliably received?

The narrow bandwidth and quadrature phase shift keying (QPSK) modulation.

According to the FCC, the leakage log should contain which of the following?

The probable cause of the leakage.

During aerial plant construction,

The strand is tensioned so its sag profile matches that of the overhead utility power lines.

What characteristic of foldback limiting circuitry protects equipment if the load is accidentally shorted?

The supplied voltage and current drops to near-zero or zero when maximum current limit is reached.

Why is 38 MHz typically the highest frequency in the sub-band frequency that is used for upstream modem transmissions?

The upper edge of the sub-band frequency spectrum is prone to group delay caused by the duplex filters.

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?

The value of the attenuator pad at the input of the STB demodulator.

What is the FCC specification regarding repair of leakage of the 20 uv/m level?.

There is no FCC specified time.

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?

These frequencies are at the edges of the return frequency spectrum and are available.

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?

These variations are normal and Can Usually be disregarded,

What is a characteristic of orthogonal frequency division multiplexing (OFDM) channel subcarriers?

They can be modulated at the maximum order of modulation for a given bandwidth that is suitable for the condition of the network.

Why does the output level from customer premises equipment (CPE) vary?

To compensate for variable amounts of attenuation in the return path of each device.

What purpose do diplex filters fulfill when installed at the input and output of a two- way amplifier module?

To route the forward and return signals over different circuit paths to the appropriate section so that they can be amplified separately.

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.

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 is the return path considered to be properly balanced with unity gain?

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 characteristic of a ferroresonant power supply provides voltage regulation as the source voltage changes?

With the flux in the core saturated, then the secondary voltage remains constant as the primary voltage changes.

Chipsets with ingress cancellation algorithms are most effective for removing impairments in what portion of the RF return frequency spectrum?

Within the upstream channel bandwidth

In a basic step-up switcher circuit design, what is the relationship of the square- wave duty cycle to the output voltage?

The larger the duty cycle, the higher the voltage.

House amplifiers with a passive return path are used for what type of situation?

For situations when long service drops are used and the forward path needs to be amplified but return path amplification is unnecessary.

Verifying plant reliability includes

Frequency response sweeping, which is adjusting RF amplifier circuits to amplify all frequencies in the bandpass spectrum as equally as possible

RF trunk amplifiers

Have attenuator pads, equalizers, and duplex filters that control and route the RF signals.

When should a preamplifier be used to measure impairments with a spectrum analyzer?

If the noise floor drops less than 10 dB when the input signal is removed from the spectrum analyzer.

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?

Regardless of the frequency, if the impulse noise or ingress is high enough, it can cause laser clipping.

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?

STB and DOCSIS modems are assigned different upstream channels with dedicated receivers in the headend.

In a feedback linear regulator, what enables a stable output voltage while enabling a wide range of output current through the load?

The current across the Zener diode is constant.

If the power out of a transformer must equal the power in, assuming zero efficiency loss, what happens to the output current when the transformed output voltage is 10% lower?

The current increases 10%.

What happens to the data throughput when transitioning from quadrature phase shift keying (QPSK) to 16-QAM (quadrature amplitude modulation) in a channel of the same bandwidth?

The data throughput doubles.

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.

In a series-pass transistor regulator, which component isolates the Zener diode from changes in the load for improved voltage regulation.

The emitter follower configured transistor (series-pass transistor).

With underground plant construction,

The fiber-optic and coaxial cables are often places underground with other utility lines to jointly share construction costs.

What information can be gathered by a return path monitoring system that captures the quadrature amplitude modulation (QAM) return channel from a DOCSIS modem?

The group delay, in-band ripple/tilt, and micro-reflections on the QAM channel.

Standby power supplies

continue providing an output voltage even during a utility power outage by using a back up power source.

The forward path signal in a traditional tree-and-branch architecture

originates at the headend and is transmitted downstream through coaxial trunk cable and trunk amplifier.

Centralized power configurations

provide the advantage of increased reliability through sharing of expensive backup generators and sophisticated monitoring equipment among different power realms.