ROC I - Supplemental Questions Part 2

What does a time domain reflectometer (TDR) measure?

A TDR measures the presence of and distance to cable faults.

Describe the function of a basic feed-through tap.

A basic feed-through tap passes both the RF signals and the AC powering voltage from the input port to the output port while directing a small portion of the input RF signal to each tap port.

What is the purpose of a coaxial express cable in an HFC distribution system?

A coaxial express cable allows a particular optical node to reach farther out in the distribution system.

What does a combination SLM/leakage detector measure?

A combination SLM/leakage detector incorporates the features of both an SLM and a signal leakage detector.

What does a digital multimeter (DMM) measure?

A digital multimeter (or VOM) measures AC and DC voltages, resistance for continuity checks, and current.

What is the purpose of a diplex filter?

A diplex filter separates or combines the higher-frequency forward RF signals from the lower-frequency return RF signals.

What is a high-pass filter?

A high-pass filter is a type of bandpass filter that passes all frequencies above a specific frequency (e.g., 50 MHz), and eliminates common path distortions, impulse noise in the return spectrum, and any other frequencies that fall below that specific frequency.

What does a signal leakage detector measure?

A signal leakage detector is an RF receiver with an installed input antenna that measures broadband cable signals leaking from the system within FCC assigned aeronautical frequency bands.

What types of gaskets typically are used between the housing and housing cover?

A silicone rubber environmental gasket and the metal mesh radio frequency interference (RFI) gasket typically are used between the housing and housing cover.

How can a distribution system design map aid the troubleshooting process, after gathering as much information as possible about the extent of the affected area?

A system design map is used to analyze system for the device common to the customers so far affected before traveling to make additional signal status checks.

Why does the terminating tap faceplate not have an output port interconnect pin?

A terminating tap faceplate does not have an output port interconnect pin because it does not pass any signals to the output port.

Does a terminating tap have an output port signal?

A terminating tap has no need for an output port signal and, therefore, does not pass any RF signals or AC voltage to its output port.

Where does the feeder system forward path start and end in a tree-and-branch design?

A tree-and-branch feeder system forward path starts at the output of the bridger amplifier module in the trunk/bridger amplifier station and ends at the tap port of an RF tap.

What is a typical AC voltage range for a line extender amplifier?

A typical AC voltage range for a line extender amplifier is within 30-72 VAC root mean square (RMS).

What is the function of addressable taps?

Addressable taps can control cable service activation and the level of authorized services from a central office location, often eliminating many costly truck rolls.

List and describe the purposes of the two types of gaskets found in all common power inserters.

All common brands of power inserters have an aluminum-screen RFI gasket to prevent undesired RF signal ingress and egress and a silicone rubber environmental gasket to keep out moisture and contaminants.

Where does the distribution system forward path begin and end in an HFC design?

An HFC distribution system forward path begins at the output of an RF amplifier located in the optical node and ends at the tap port of an RF tap.

What does a signal level meter (SLM) measure?

An SLM measures individual analog video and audio, and digital carrier levels.

Why are taps with lower tap values installed as the distance from the amplifier increases?

As the distance from the amplifier increases, taps with lower values are installed to ensure each customer receives an adequate signal level.

What happens when light encounters a medium with a different index of refraction?

At a steep angle (greater than the critical angle), the light is bent or refracted as it passes from one medium into another. Light that strikes the new medium at a shallow angle (at or less than the critical angle) is reflected back to the original medium.

What is the proper troubleshooting technique?

Begin at a location common to all known outage sites, divide the area of unknown signal status in half, verify the signal condition, and repeat (if necessary) until the source of the problem is found.

List the common amplifier controls and explain their specific functions.

Common amplifier controls include: (1) slope control, which further adjusts the tilt of the RF output signals to compensate for the known attenuation effects of the coaxial cable; and (2) signal level control, which compensates for slight variations in the input signal level caused by temperature changes and by signal loss from coaxial cable and passive devices.

List the common amplifier plug-in passive components and explain their specific functions.

Common amplifier plug-in passive components include: (1) attenuator pads, which reduce the amplitude of the forward or return path RF signals; (2) equalizers, which compensate for the unequal signal level attenuation caused by the coaxial cable; and (3) filters, which separate or block specific frequencies.

Which tap port configurations are available in common brands of feed-through and terminating taps?

Common brands of feed-through and terminating taps are available with two-, four-, and eight-port configurations.

What are decibels used for?

Decibels are used to compare power levels. The two powers do not have to be measured in the same impedance because power is power, regardless of the impedance in which it is measured.

What does eliminating a discovered signal leak accomplish?

Eliminating a discovered leak averts a potential outage or trouble call.

What are the two glass sections of which fiber is composed?

Fiber is composed of two glass sections, the core and the cladding.

List five RF distortion specifications associated with RF amplifiers.

Five RF distortion specifications associated with RF amplifiers are: (1) composite triple beat (CTB); (2) composite second order (CSO); (3) cross modulation; (4) hum; and (5) noise figure.

List and explain four RF operating specifications typically associated with RF amplifiers.

Four RF operating specifications typically associated with RF amplifiers are: (1) forward passband — the band of passable forward RF amplifier input signals; (2) return passband — the band of passable return RF amplifier input signals; (3) operational gain — the signal level difference between the input signal and the output signal; and (4) forward and return output levels — the output signal levels dependent upon system requirements and setup procedures.

Explain the purpose of fuses and/or circuit breakers in a line extender amplifier.

Fuses and circuit breakers in line extender amplifiers protect the circuitry against damage caused by an excessive amount of current and also bypass or direct AC voltage to and from different housing ports.

What is one of the basic principles of resistance reflected in the familiar practices of grounding and bonding?

Grounding and bonding practices reflect the basic principle that electricity always follows the path of least resistance.

How does hum modulation display itself in an analog TV picture?

Hum modulation shows up as one or two horizontal bars moving vertically through an analog TV picture.

Describe the two loss components that combine to make up the total tap loss of an eight-way feed-through tap.

In an eight-way feed-through tap, total tap loss is a combination of the loss: (1) on the tap leg of the directional coupler portion of the tap; and (2) at each of the three levels of signal divisions within the splitter network portion of the tap.

What is the function of an optical receiver in the downstream path?

In the downstream path, the optical receiver converts light back to RF signals and the signals are then amplified for distribution over coax to customer premises equipment (CPE).

What is a tap's insertion loss, and how does it vary with frequency?

Insertion loss is the signal attenuation between the tap's input port and output port. Generally, as the RF signal frequency increases, the insertion loss increases.

What is the effect of installing or removing a power inserter fuse?

Installing or removing a power inserter fuse passes or blocks AC voltage from the AC input port to an RF/AC port.

Besides frequency, what are four differences between light and RF?

Light carries more information over fiber than RF can over coax. Light is unaffected by interference from lightning or other electrical sources, whereas RF is highly susceptible to these factors. In addition, light does not interfere with any other signals or cause electrical sparks. RF can interfere with other signals within the cable and, in the case of signal leakage, interfere externally. Signals that travel over light are not easily intercepted and decoded illegally.

What active devices on a feeder cable receive AC power passed by taps?

Line extender amplifiers receive AC power that is passed by taps on a feeder cable.

What tasks are involved in maintaining physical plant integrity within the distribution system?

Maintaining physical plant integrity involves: (1) checking and tightening loose connectors, housing enclosures, and tap face plates; (2) lubricating pedestal and power supply padlocks periodically during normal access; and (3) securing and documenting any broken lashing wire to prevent further deterioration.

List several methods used to accomplish signal level control.

Methods that accomplish signal level control are: (1) manual gain control; (2) automatic gain or level control; and (3) thermal level control.

What is the difference between multimode and single-mode fiber?

Multimode fiber provides more than one path through the core at the same time, while single-mode fiber passes light through a single path. Single-mode fiber has less attenuation or signal loss caused by light colliding with the fiber cladding or dispersing as it spreads through the fiber.

How often are outages caused by equipment failures?

Outages caused by equipment failures generally occur less frequently than other outage categories.

What are the four common directional coupler electrical characteristics?

Output loss is the loss the signal experiences as it goes from the input to the output of the directional coupler; tap loss is the reduction in the input power desired to go to the tap port of the directional coupler; isolation is a measure of the amount of signal entering the tap port that reaches the output port; and return loss is the worst-case measurement at any port and is a measure of how much signal entering a port is "turned around" and sent in the direction it just came from.

What happens if there is poor return loss in a cable network?

Poor (low) return loss in a cable network can produce ghosting in analog systems, and can produce echoes and suck-outs in digital signals, making the desired signal harder to demodulate and turn into useful bits.

What RF and/or AC electrical specifications are significantly different for power inserters compared to RF line splitters and directional couplers from the same manufacturer?

Power inserter specifications for power passing, isolation, and insertion loss are significantly different from those specifications for RF line splitters and directional couplers from the same manufacturer.

What are six performance checks involved in maintaining power supplies?

Power supply performance checks include: (1) AC input voltage; (2) AC output voltage; (3) output current (amperage) draw; (4) individual battery voltages; (5) charging (float) voltages; and (6) standby switching capability.

What are six sources of outages caused by powering failures?

Powering failures include: (1) a utility power failure; (2) a tripped utility breaker; (3) spent standby battery power; (4) a blown distribution leg fuse; (5) a blown amplifier DC power supply fuse; and (6) a cable center conductor suck-out.

List several things to do prior to closing the line extender amplifier housing cover.

Prior to closing the line extender amplifier housing cover: (1) visually inspect the housing for any damage; (2) confirm that all required gaskets are in place; (3) inspect the gaskets for wear or damage (and replace, if necessary); (4) confirm that all required gaskets are dry and free of contaminants; (5) avoid pinching any cords or cables between the housing and the housing cover while closing the housing cover; and (6) check the looseness of the hinge bolts to ensure that the housing cover closes easily.

How are directional couplers built?

RF directional couplers are built using multiple RF transformers, with the windings on suitable ferrite coil forms, which allow selected amounts of the signal to be removed.

Describe how the routing of RF signals in a terminating tap differs to that in a feed-through tap.

RF signals in a terminating tap are routed directly to the splitter network in the tap, while in a feed-through tap the RF signals are routed first to the directional coupler portion and then to the splitter network portion of the tap.

What is refraction?

Refraction refers to the changes in light's behavior as it passes from one medium into another.

What is the advantage of using an RF/AC bypass tap over a basic tap design?

Removing the faceplate of a basic tap has the undesirable effect of disconnecting the cable service for all customers downstream from that point, and the RF/AC bypass tap avoids this problem by having the added ability to maintain RF signal and AC voltage continuity during tap faceplate removal.

What is return loss in a tap?

Return loss is an indicator of the amount of signal reflected by a tap.

List and describe several types of ports on line extender amplifier housings.

Several types of ports found on line extender amplifier housings are: (1) an input port for receiving the forward RF signals; (2) one or two output ports for distribution of the amplified forward RF signals downstream; (3) external RF test ports that permit direct access for measuring RF input and output signals without opening the housing cover; and (4) external test port holes that permit access to internal RF test points without opening the housing cover.

List several ways in which slope control is accomplished.

Several ways in which slope control is accomplished are: (1) a plug-in equalizer and interstage equalizer; (2) a slope control adjustment; and (3) an automatic slope control.

Describe how brands of taps differ in their interchangeability of faceplates with housings.

Some brands of taps have interchangeable faceplates that will fit any housing in the brand name series, while other brands have interchangeable two-way and four-way faceplates with a different housing required for the eight-way faceplate.

What RF and/or AC electrical specifications are identical or similar among power inserters, RF line splitters, and directional couplers in a brand name series?

Specifications for hum, bandwidth, and return loss are identical or similar among power inserters, RF line splitters, and directional couplers in a brand name series.

Which symbols represent two-way, four-way, and eight-way taps and tap values on standard cable system design maps?

Standard cable system design maps represent a two-way tap as a circle, a four-way tap as a square, and an eight-way tap as a hexagon, with the tap value number inside the symbol.

Describe typical residential settings for the use of two-way, four-way, and eight-way taps.

Systems commonly use two-way taps where you can access only one or two homes from a location on the feeder cable. In more densely populated areas, systems use four-way taps along back easements and alleys where one location can serve four homes. Eight-way taps are used individually in a cluster of residences, or they are connected together in MDU lock boxes.

Define tap loss.

Tap loss is the signal attenuation between the input port and each customer tap port at a specific frequency.

What does tap-to-port isolation inhibit?

Tap-to-port isolation inhibits undesired RF signals on the output port from interfering with desired RF signals on any of the customer tap ports and vice versa.

What does tap-to-tap isolation inhibit?

Tap-to-tap isolation inhibits undesired RF signals on one customer tap port from interfering with the desired RF signals on another customer tap port.

Define the two types of isolation in taps.

Taps have: (1) tap-to-tap isolation, which is the signal attenuation between any two individual customer tap ports at a specific frequency, with all other ports terminated; and (2) tap-to-port isolation, which is the signal attenuation between the output port and any individual customer tap port at a specific frequency, with all other ports terminated.

List the test points typically found on line extender amplifiers.

Test points typically found on line extender amplifiers are: (1) AC test points for measuring the input and output AC voltage; and (2) DC test points for measuring the DC power supply voltage.

Describe the AC voltage distribution in a typical line extender amplifier.

The AC voltage in a typical line extender amplifier is received through the input port seizure screw connection on the housing and directed to the DC power supply through plug-in connectors located on the housing base under the amplifier module. The AC voltage also can be routed to the output port or directed from the output port to the DC power supply.

What is the DC voltage requirement of the DC power supply in a line extender amplifier?

The DC voltage requirement of the DC power supply in a line extender amplifier is +24 VDC.

What components are on the back of the tap housing?

The back of the tap housing has: (1) a threaded mounting tap and strand clamp; (2) and a strip gauge for measuring the required length of the pin connector's pin or the coaxial cable's center conductor.

What is the coaxial cable voltage loss on the cable between the power supply and the power inserter when: (1) the cable length is 150'; (2) the cable's DC loop resistance is 1.07 Ω/1,000'; and (3) the total current requirement for amplifiers supplied by that power inserter is 11 A?

The coaxial cable voltage loss is 1.76 VAC on the cable between the power supply and the power inserter when the cable length is 150', the cable's DC loop resistance is 1.07 Ω/1,000', and the total current requirement for amplifiers supplied by that power inserter is 11 A. To calculate: (150 ÷ 1,000) × 1.07 = 0.16 Ω; 0.16 × 11 = 1.76 VAC.

What is the purpose of the cooling pins or fins on the outside of the amplifier housing?

The cooling fins or pins on the outside of the amplifier housing dissipate heat generated by the RF amplifier module and DC power supply.

What are the differing forward-path transmission bandwidths for traditional tree-and-branch and HFC architectures?

The feeder system in a traditional tree-and-branch architecture supplies the forward signal up to a 50-550 MHz pass band, and the distribution system in an HFC network transmits the forward signal up to a 50-1,000 MHz pass band.

What forward frequency ranges typically are used in new and upgraded broadband cable systems?

The forward frequency ranges typically used in new and upgraded broadband cable systems are 50-550 MHz and 50-860 MHz.

How does the insertion loss value vary with the tap loss value within a full range series of taps?

The greater the tap loss (i.e., the larger the tap value), the smaller the insertion loss value.

What comprises the impedance of a coaxial cable or a device (connector, passive, etc.)?

The impedance comprises the combined effects of a coaxial cable's or a device's resistance, inductance, and capacitance.

What is a consequence of getting more signal out of the tap port?

The inevitable consequence of getting more signal out of the tap port is that there is less signal available for the output port.

What is the input port RF signal level for a four-way feed-through tap at 50 MHz when: (1) the preceding tap's output port signal level is 30.0 dBmV at 50 MHz; (2) the cable length between the two taps is 130 feet; and (3) the cable loss specification is 0.54 dB/100 feet at 50 MHz?

The input port RF signal level for a four-way feed-through tap is 29.3 dBmV at 50 MHz when: (1) the preceding tap's output port signal level is 30.0 dBmV at 50 MHz; (2) the cable length between the two taps is 130 feet; and (3) the cable loss specification is 0.54 dB/100 feet at 50 MHz. To calculate: (1) 0.54 dB/100 feet × 1.30 = 0.7 dB (rounded off); and (2) 30.0 dBmV - 0.7 dB = 29.3 dBmV.

What are the input port and individual customer tap port RF signal levels for an eight-way feed-through tap at 550 MHz when: (1) the preceding tap's output port signal level is 35.0 dBmV at 550 MHz; (2) the cable length between the two taps is 120 feet; (3) the cable loss specification is 1.82 dB/100 feet at 550 MHz; and (4) the tap loss is 17.8 dB at 550 MHz?

The input port RF signal level is 32.8 dBmV and the individual customer tap port RF signal level is 15.0 dBmV for an eight-way feed-through tap at 550 MHz when: (1) the preceding tap's output port signal level is 35.0 dBmV at 550 MHz; (2) the cable length between the two taps is 120 feet; (3) the cable loss specification is 1.82 dB/100 feet at 550 MHz; and (4) the tap loss is 17.8 dB at 550 MHz. To calculate the input port level: (1) 1.82 dB/100 feet × 1.20 = 2.2 dB (rounded off); and (2) 35.0 dBmV - 2.2 dB = 32.8 dBmV. To calculate customer tap port level: 32.8 dBmV - 17.8 dB = 15.0 dBmV.

What does an interstage equalizer provide?

The interstage equalizer provides additional slope to the forward RF signals.

What is the purpose of the low-pass coil in a tap's circuitry?

The low-pass coil in a feed-through tap passes the 60 Hz AC voltage directly between the input port and the output port while blocking the higher frequency RF signals, which are instead routed through the directional coupler portion of the tap.

What are measurement applications for using SLMs, DMMs, TDRs, leakage detectors, and combination leakage detectors?

The measurement applications include: (1) balancing amplifier (bridger, distribution, and line extender) output levels (SLM); (2) verifying system and amplifier power supply operation (DMM); (3) identifying cut or damaged cable spans (TDR); (4) identifying sources of ingress (signal leakage detector, SLM); and (5) monitoring and measuring signal leakage (egress) for system CLI reporting (combination SLM/leakage detector).

What is the most common type of line extender amplifier?

The most common type of line extender amplifier is the power-doubling amplifier.

What are three groups of outage causes associated with cut or damaged cables?

The outage groups are: (1) cables cut by underground digging equipment (a backhoe, a trencher, a post-hole digger, a shovel, etc); (2) aerial cable damaged by lightning or downed power lines; and (3) downed aerial cable due to traffic accidents or severe weather.

What are the output port and individual customer tap port RF signal levels for a four-way feed-through tap at 50 MHz when: (1) the input port signal level is 29.3 dBmV at 50 MHz; (2) the insertion loss is 1.1 dB at 50 MHz; and (3) the tap loss is 20.0 dB at 50 MHz?

The output port RF signal level is 28.2 dBmV and the individual customer tap port RF signal level is 9.3 dBmV for a four-way feed-through tap at 50 MHz when: (1) the input port signal level is 29.3 dBmV at 50 MHz; (2) the insertion loss is 1.1 dB at 50 MHz; and (3) the tap loss is 20.0 dB at 50 MHz. To calculate the output port level: 29.3 dBmV - 1.1 dB = 28.2 dBmV. To calculate the customer tap port level: 29.3 dBmV - 20.0 dB = 9.3 dBmV.

What is the purpose of the plug-in connectors on the inside of the line extender amplifier housing base?

The plug-in connectors on the inside of the line extender housing base: (1) direct the incoming forward RF signals from the input port to the RF amplifier module; (2) direct the outgoing amplified signals from the amplifier module to the output port; and (3) direct AC and the return RF signals to and from the RF amplifier module.

Summarize how the regulated +24 VDC voltage is produced in a line extender amplifier.

The regulated +24 VDC voltage in a line extender amplifier typically is converted from the AC input voltage by a switching DC power supply.

What is the purpose of the return RF amplifier module?

The return RF amplifier module amplifies the return signals for transmission to the next return amplifier upstream.

What determines selection of tap value?

The selection of a tap value depends on the tap's location on the feeder cable in relation to the output of the nearest optical node or upstream bridger or line extender amplifier. In general, the closer the tap is to an amplifier's output, the higher the tap value.

What does each housing gasket prevent when the housing cover is properly closed?

The silicone rubber gasket prevents dirt, water, and pollutants from entering the RF amplifier module area, and the metal mesh RFI gasket prevents ingress and egress of RF signals when the housing cover is properly closed.

Explain the purpose of surge protection devices and their typical location in a line extender amplifier.

The surge protection device used in line extender amplifiers protects the electronics circuitry against damage caused by voltage and current surges from lightning, power line faults, and system voltage spikes. The surge protection device typically is located near the AC voltage inputs.

What two ways can the tap's faceplate label identify a tap's value?

The tap's faceplate label can identify the tap's value by: (1) the tap value printed on the label; and (2) the color-coded label.

What are three principle characteristics that define an AC waveform?

The three principle characteristics that define an AC waveform are: (1) frequency; (2) wavelength; and (3) amplitude.

What are the three steps to open a C-COR line extender amplifier housing?

The three steps to open a C-COR line extender amplifier housing are: (1) partially loosen the six captive lid bolts with a 7/16-inch nutdriver in the proper order; (2) hand loosen and release bolts one through five; and (3) while holding the lid closed with one hand, release the last bolt and lower or open the lid.

What is the range of typical minimum return loss values for common brands of taps?

The typical minimum return loss values are 15-20 dB for the input, output, and tap ports of common brands of taps.

What additional layers compose the fiber cable?

There are additional layers that compose the fiber cable. Lightweight fiber strands usually are placed inside protective loose buffer tubes to reduce damage. It also can contain strength members, jackets, and armor to protect individual fibers.

List three common return frequency bands associated with return amplifier modules.

Three return frequency bands associated with return amplifier modules are the sub-split band, the mid-split band, and the high-split band.

To increase the customer tap port signal level in an installed tap, should the new, replacement faceplate have a larger or smaller tap value number than the original faceplate?

To increase the customer tap port signal level in an installed tap, the new replacement faceplate should have a smaller tap value number than the original faceplate.

What are the typical wavelengths or "windows" for light transmission over fiber in a cable system?

Typical wavelengths or "windows" for light transmission over fiber in cable systems are 1,310 nm (nanometers) and 1,550 nm.

What is reflection?

When a ray of light strikes something, such as a flower, it reflects or bounces off and spreads out in all directions. Some of that reflected light is caught by our eyes, allowing us to recognize the flower and its color.

What should you always do when tightening the line extender amplifier housing cover bolts?

When tightening the line extender amplifier housing cover bolts, always follow the manufacturer's recommended torque and tightening sequence.

You can divide the RF signal distribution components of a feed-through type tap into which two portions?

You can divide the RF signal distribution components of a feed-through tap into a directional coupler portion and a splitter network portion.

Where do you install a terminating tap installed on the feeder cable?

You install a terminating tap at the end of a feeder cable run as the last tap.