Final Exam Review

These flashcards cover key concepts from the final exam lecture notes.

How was the bel divided to become a workable unit of measurement?

It was divided into 10 equal units called the dB.

Which of the following best describes a number that compares an amount less than the whole to the whole amount?

A fraction.

How do you convert a fraction to a percent?

Dividing the numerator by the denominator and multiplying by 100.

The starting point of the entire decibel measurement system is the bel, which is clearly defined as a power ratio.

10:1.

Which of the following best describes one-tenth bel or 1 dB?

Half the ratio of a 1 bel ratio.

An input-to-output power ratio of 10:1 has an input-to-output voltage ratio of .

3.162:1.

What is the input-to-output power ratio of 2 bels of a similar impedance cable?

100:1.

What is the minimum acceptable signal level of 0 dBmV at TV set inputs?

1 mV across 75 ohms.

Which represents the values expressed in dBmV preceded by a minus sign (-)?

Values of voltage less than 1 millivolt (mV) across 75 ohms.

A signal increase of 1 dB represents a ___ increase in power.

10%.

Why do values expressed in dBmV progress nonlinearly compared to a linear mV?

They are based on the logarithms of power ratios.

What is approximately equivalent to a 1 mV decrease in a signal level of 40 dBmV?

A decrease in the level of 3 dBs.

What are the units that can be used to represent signal level values?

mV, dBmV, and μW.

How much signal is necessary from the subscriber's tap port at 750 MHz to provide a minimum of 3.0 dBmVs to the TV set when the drop is 150 feet of Series 6 cable?

8.7 dBmV.

What is the maximum tap value that can be installed connected to a line extender amplifier output?

37 dB.

What happens to a signal when the output of a line extender is 3 dB lower than it normally should be?

The signal power is 25.89% low.

To maintain a 3 dBmV input signal to two TVs, what would be the minimum signal level at the tap if the drop is 150 feet long?

19 dBmV.

Which DOCSIS layer is used by the CMTS to differentiate between cable modems?

The DOCSIS MAC.

What was introduced in DOCSIS 3.0 to allow enough bandwidth for upstream carriers?

The option to increase the top frequency of the upstream to 85 MHz.

What would be the downstream throughput if two QAM channels with a throughput of 38 Mbps were bonded?

76 Mbps.

Why is the data throughput over the return or upstream path typically less than over the forward path?

The narrower bandwidths and lower transmit power of the modems used to transmit data.

What are two features added in DOCSIS 3.1 to extend the viability of HFC networks?

OFDMA and LDPC.

How does IP multicast differ from IP broadcast?

IP multicast traffic is only sent to specific modem addresses on the network.

Which step in the troubleshooting process requires a discussion with the customer?

Step 1: Identify the problem.

What can a technician learn by asking the customer to show or demonstrate the problem?

The symptoms of the problem can be viewed.

What is the minimum MER into the cable modem for a 256-QAM carrier?

32 dB or greater.

What layers of the OSI reference model are specific to cable networks?

Layers 1 through 4 are applied between the DOCSIS modem and CMTS.

What are the signal leakage limits for analog signals less than 54 MHz?

17.4 µV/m at 30 meters.

Which frequencies are the aeronautical frequency bands?

108-137 and 225-400 MHz.

What leakage levels must the FCC log and repair?

50 µV/m and above measured 20 feet from the cable.

What is used for verifying the leakage detector's calibration?

A multi-element directional antenna.

What automatically captures the location of leakage data?

GPS-assisted leakage measurement instruments.

How can the proper operation of a leakage detector be verified?

By testing the leakage detector on the bench.

What is the purpose of a tagger when detecting signal leakage?

Ensures any leak measured emanates from the cable system.

What unit is used to identify the field strength of electromagnetic radiation?

µV/m.

What type of antenna does the FCC require for measuring signal leakage?

Near field.

In the tree-and-branch architecture, how is the downstream signal fed to the distribution branches?

The downstream is split after each amplifier.

What is the RF distribution tap value indicated on the tap's face plate?

The signal loss between the tap downstream input port and the tap ports.

What is a common solution when there is congestion from modem activity?

Node splitting.

How can a technician identify non-standard symbols on network design maps?

The standardized map symbol document.

What technologies are defined in DOCSIS 4.0 to sustain the HFC network?

FD and DAA.

How can a distribution amplifier be identified on a network design map?

It has a large identifying label.

What is spliced into the hardline coaxial cable to combine AC power with RF signal?

A power inserter.

What test instrument sends out a test signal to display reflections from cable faults?

TDR.

What do you check when analyzing network design maps for troubleshooting?

How far the affected customers are from the fiber node.

What is required for checking physical network integrity?

Being observant and performing minor tasks while engaged in scheduled activities.

What do all hardline splitters have on the back?

A threaded mounting tap and strand clamp.

What can be done in tight quarters when installing hardline equipment?

The hardline coaxial cable connectors can be attached at the end of the housing.

What is on the interior side of the faceplate of directional couplers?

The electronic circuitry and interconnect pins.

What is the relationship of the insertion loss in a directional coupler?

The insertion loss remains constant regardless of the signal tapped from the input.

What component determines to which ports 60/90 VAC is sent in splitters or couplers?

A transformer.

How is the port-to-port isolation measured in a splitter?

Connect a SLM to the common input port.

What impact does a power inserter have on RF in a network?

It should have minimal impact on the RF in both directions.

How does a power inserter function?

It contains a high-pass filter network to block AC voltage.

Why is it necessary that feed-through distribution taps pass AC?

To pass AC along to power other amplifiers downstream.

What type of map can be used for tracking network upgrades?

A design map.

Why are network design maps drawn on a specific scale?

To capture and display the details of the network.

What do small circles with an X represent on a network design map?

There is no place to attach cable.

What do squares with numbers represent in network maps?

4-port distribution taps.

Which hardline coaxial cable splicing project is in the repair category?

Splicing in an address that was missed in the original design.

How can you identify the high-output port of an unbalanced 3-way splitter?

The high-output port is indicated by a dot on the map symbol.

What can be done to find cable direction if forgotten during splicing?

Attach a cable locator to each cable.

When can a single straight splice connector be used?

If the crack is in the flat straight section of an expansion loop.

Why measure signals at the highest and lowest downstream channels?

To ensure signal levels are within specification.

What should be used instead of short coaxial cable jumpers?

Housing-to-housing adapters.

What entity approved the first version of DOCSIS?

The ITU.

What criteria does the DOCSIS certification process ensure?

Compliance with the DOCSIS standard.

Which layers of the OSI model are specific to cable networks?

Layers 1 through 4 are applied between the DOCSIS modem and CMTS.

What access technology does DOCSIS 1.0 use to send data upstream?

TDMA.

What was needed for PacketCable to deliver quality telephone service?

QoS controls, enhanced security, and higher orders of modulation.

What features were introduced in DOCSIS 3.1 for better throughput?

OFDM and LDPC.

Which DOCSIS version raised the frequency of upstream spectrum to 85 MHz?

DOCSIS 3.0.

Why are data throughput rates asymmetrical in DOCSIS networks?

The narrower bandwidths and lower orders of modulation for the return path.

Which OSI model layers does the MAC Layer in the DOCSIS overlap?

The Data Link and Internet Layers.

Where do DOCSIS modems receive their configuration files from?

From the CMTS, which interfaces with the OSS.

How do STBs and DOCSIS modems operate as separate systems?

Diplex filters separate their upstream channels.

What did DOCSIS 1.1 introduce for real-time data applications?

PacketCable.

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

A many-to-one system.

Why is 38 MHz typically the highest frequency for upstream modem transmissions?

The coaxial cable tends to roll off at that frequency.

What enables the STB upstream carrier to be reliably received below 20 MHz?

The high-powered upstream transmission levels and FEC.

What do house amplifiers with a passive return path serve to do?

For customer premises receiving only downstream signals.

What causes variations in output levels from CPE?

Each CPE manufacturer sets their output level.

What is the return path attenuation loss through an unbalanced three-way splitter?

9.0 dB.

What purpose do diplex filters serve in a two-way amplifier?

To route forward and return signals.

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

At sub-band frequencies, the signal attenuation is flat.

What should be done before diagnosing a return path problem?

Confirm that the HFC network is working properly.

Which spectrum analyzer function captures ingress and noise?

The Max Hold function.

What should be done when electrical interference is identified?

Notify the power company about the exact location.

What can check the drop system for RF continuity at sub-band frequencies?

A signal generator.

What data can a return path monitoring system capture?

The modem's return path data throughput.

What feature of DOCSIS PNM saves troubleshooting time?

PNM correlates data from all modems to pinpoint likely problems.

When should a preamplifier be used with a spectrum analyzer?

When the input signal is less than 0 dBm.

What does the Zero Span function do on a spectrum analyzer?

It stops the analyzer's sweep and parks its tuner to a specific frequency.

How is laser clipping characterized on a spectrum analyzer?

By an elevated noise floor above 42 MHz.

Why is it a good idea to begin troubleshooting at low value taps for impulse noise?

Low value taps have less shielding.

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

QPSK.

How many decimal values can eight bits of data represent?

256.

What is a characteristic of OFDM channel subcarriers?

They can be modulated at the maximum order of modulation.

What MAC protocols are specified for digital STBs?

S-CDMA and A-TDMA.

What advanced PHY technology was added to DOCSIS 2.0?

S-CDMA.