Cable Television Basics
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Questions and Answers

What frequency is associated with the video or picture carrier on midband cable TV channels?

  • 121.25 MHz (correct)
  • 126 MHz
  • 125.75 MHz
  • 120 MHz

Which channels are included in the midband category?

  • Channels 00, 01, and 54 to 59
  • Channels 23 to 37
  • Channels 2 to 13
  • Channels 14 to 22 and 54 to 59 (correct)

What is the primary purpose of the separate converter unit provided by the cable operator?

  • To convert cable frequencies to a designated VHF channel (correct)
  • To provide a clearer picture on high-definition TVs
  • To enhance channel selection on conventional TVs
  • To boost signal strength for better quality

How does the cable operator attempt to manage cable radiation?

<p>By ensuring cables are properly terminated (C)</p> Signup and view all the answers

What is the starting channel designation for the superband cable TV channels?

<p>Channel 23 (A)</p> Signup and view all the answers

What is the significance of using double digits for cable channel numbers?

<p>To enable a digital control board for tuning (B)</p> Signup and view all the answers

Which feature is commonly built into converters for premium pay services?

<p>Scrambling circuits (D)</p> Signup and view all the answers

Why are systems utilizing higher cable channels up to 400 MHz considered more sophisticated?

<p>They require special cable and better amplifiers (C)</p> Signup and view all the answers

What is the primary purpose of using a portable FM radio as a 'sniffer' for radiation detection?

<p>To locate radiation by detecting specific frequencies. (A)</p> Signup and view all the answers

Which frequency is mentioned as being sensitive in relation to radiation detection?

<p>121.5 MHz (C)</p> Signup and view all the answers

What is the key advantage of using harmonically related channels (HIRCs) in cable systems?

<p>They simplify the frequency synthesis circuits for tuning. (D)</p> Signup and view all the answers

What is the function of the central wire in coaxial cable?

<p>To carry the CATV signal as the inner conductor. (A)</p> Signup and view all the answers

What construction material is used for the heavy central conductor in trunk lines?

<p>Copper-clad aluminum. (B)</p> Signup and view all the answers

Which of the following statements regarding cable diameter and attenuation is true?

<p>Larger cable diameter generally reduces attenuation. (B)</p> Signup and view all the answers

What feature aids the flexibility of the coaxial cable during installation?

<p>Hollow structure with plastic beads. (C)</p> Signup and view all the answers

How does a steel messenger cable function in cable installations?

<p>It supports the weight of the cable over long spans. (A)</p> Signup and view all the answers

What is a primary advantage of using fiber-optic cable for long-distance communication?

<p>Lower attenuation of signals (C)</p> Signup and view all the answers

How does the use of internal reflection in fiber optics contribute to signal transmission?

<p>It enables multiple light frequencies to be transmitted simultaneously (D)</p> Signup and view all the answers

What happens to light rays as they enter a denser medium like glass?

<p>They are bent towards the normal line (A)</p> Signup and view all the answers

What characterizes the signal-to-noise ratio of FML compared to AML in communication systems?

<p>FML generally has a better signal-to-noise ratio (B)</p> Signup and view all the answers

What is the role of a photoelectric detector in a fiber-optic communication system?

<p>To convert light amplitude variations back into cable signals (B)</p> Signup and view all the answers

What does the full cable-channel bandwidth allow for in fiber-optic systems?

<p>More extensive modulation of the light source (A)</p> Signup and view all the answers

What is the primary function of the small loop in the directional coupler?

<p>To tap off the signal while ignoring reflected energy (D)</p> Signup and view all the answers

What physical property of light is essential for the low attenuation observed in fiber optic cables?

<p>Internal reflection within the glass fibers (C)</p> Signup and view all the answers

What does the typical insertion loss for a directional coupler at 300 MHz indicate?

<p>Minimal loss of signal between input and output (C)</p> Signup and view all the answers

Which of the following statements about FML and AML is true?

<p>FML can perform better than FM systems using narrow frequency deviation (B)</p> Signup and view all the answers

What is the typical DC supply voltage for the cable amplifiers mentioned?

<p>24 V (D)</p> Signup and view all the answers

Why is high tap-to-tap loss desired in line taps?

<p>To provide isolation between individual subscriber lines (C)</p> Signup and view all the answers

What shape and type of cable is typically used for the drop line to the subscriber?

<p>RG 59U cable (C)</p> Signup and view all the answers

What typically happens to the power supply during AC power failure?

<p>It switches to backup storage batteries (A)</p> Signup and view all the answers

What component acts as both a capacitor and an inductor in the directional coupler?

<p>The tap loop (A)</p> Signup and view all the answers

Which of the following describes the main purpose of directional couplers?

<p>To feed a sample of the direct signal and ignore reflection (C)</p> Signup and view all the answers

What is the primary reason light is bent away from the normal when exiting a glass slab?

<p>It travels into a less dense medium. (D)</p> Signup and view all the answers

What does the index of refraction value 'n' represent?

<p>The ratio of the speed of light in a vacuum to that in the medium. (C)</p> Signup and view all the answers

When does light experience total internal reflection?

<p>When it meets the critical angle. (C)</p> Signup and view all the answers

What is the acceptance angle in a fiber-optic cable?

<p>The angle that allows complete internal reflection. (A)</p> Signup and view all the answers

What effect does modal dispersion have on optical fibers?

<p>It limits the bandwidth of the cable. (A)</p> Signup and view all the answers

What is the primary function of the cladding material in an optical fiber?

<p>To increase internal reflections. (B)</p> Signup and view all the answers

Which light ray, marked in the description, does not refract as it approaches the interface?

<p>Ray A (A)</p> Signup and view all the answers

How does the size of the fiber in optical cables relate to modal dispersion?

<p>Smaller fibers minimize modal dispersion. (B)</p> Signup and view all the answers

What was the original purpose of cable television (CATV)?

<p>To supply TV signals to communities lacking broadcast station access. (B)</p> Signup and view all the answers

How many channels can a typical cable system offer?

<p>36 channels (A)</p> Signup and view all the answers

What technology is often needed for subscribers to select their desired channel on cable TV?

<p>A cable converter box (D)</p> Signup and view all the answers

What is the challenge associated with older cable systems that distribute TV signals on VHF channel frequencies?

<p>They face adjacent-channel interference issues. (D)</p> Signup and view all the answers

Why are UHF channels converted to VHF for distribution in older cable systems?

<p>Cable losses in the UHF band are too high. (B)</p> Signup and view all the answers

What is the effect produced by adjacent-channel interference in cable systems?

<p>Windshield-wiper or venetian-blind effect (B)</p> Signup and view all the answers

How does the cable system minimize interference among channels?

<p>By balancing the signals for all channels at a common level (A)</p> Signup and view all the answers

Which frequency range is associated with mid-band cable channels?

<p>$88-108$ MHz (A)</p> Signup and view all the answers

Flashcards

Cable TV Origin

Cable TV initially served communities with poor broadcast reception due to distance or weak signals. A central antenna collected signals and relayed them to subscribers.

Cable TV's Advantage

Cable TV offers more channel options than broadcast TV because it's not restricted by government channel allocation rules.

Cable Converter Box

A cable converter box allows subscribers to select their desired channel from the numerous channels available.

Premium Cable Channels

Premium cable channels offer specialized content like current movies and sports that are not available on regular broadcast TV.

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Cable Signal Frequencies

Many older cable systems use the same VHF frequencies as broadcast TV. UHF channels are converted to VHF because cable systems have higher losses in the UHF band.

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12-Channel Cable System

This system uses both lowband and highband VHF channels, 2-13, for distribution. Subscribers do not need a converter, as their TV's tuner can select channels directly.

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Adjacent-Channel Interference

In a 12-channel system, adjacent channels can cause interference leading to a 'windshield-wiper' or 'venetian-blind' effect on the TV picture.

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Minimizing Interference

Cable systems minimize interference by balancing signal strength across all channels and keeping sound carriers lower than picture carriers.

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Midband Cable TV Channels

Cable TV channels that operate between 120 to 126 MHz, starting with channel 14 or letter A.

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Midband Channel Numbering

Midband channels are numbered sequentially from 14 to 22 (letters A to I) and include channels 00, 01, 54 to 59.

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Superband Cable TV Channels

Cable TV channels that operate above VHF broadcast channel 13, starting with channel J or number 23.

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Cable TV Channel Frequency Range

Typical cable TV systems utilize frequencies up to approximately 300 MHz for VHF and midband channels. More sophisticated systems utilize higher frequencies up to 400 MHz requiring specialized equipment.

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Cable Converter Units

A device used to convert all cable frequencies to a designated VHF channel (e.g., channel 2, 3, or 4) for standard TV receivers.

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Cable-ready TV Receivers

Modern TV receivers that can directly select midband and superband cable channels without the need for a converter.

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Scrambled Premium Channels

Channels that require decryption using a converter with built-in descrambling circuits to access content.

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Cable Radiation

Unintended emission of TV signals from cable systems caused by cable damage, mismatches, or open ends.

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HIRCs

Harmonically Related Channels (HIRCs) are cable channels operating slightly off frequencies assigned for TV broadcasting, but close enough to allow TV receivers and converters to tune them.

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Coaxial Cable

Coaxial cable is a type of transmission line used for distributing CATV signals. It consists of a central wire surrounded by a cylindrical conductor, separated by an insulator, providing efficient wideband transmission and shielding.

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Trunk Line

A main signal route in CATV distribution using coaxial cable, typically consisting of a heavy central aluminum conductor coated with copper and a solid aluminum outer shield.

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Polyethylene Foam

A material used in trunk coaxial cable to fill the internal space and support the inner conductor at the center, ensuring proper signal transmission.

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Messenger Cable

A steel cable encased within the outer jacket of coaxial cable, used to support the weight of the cable in long, unsupported spans.

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Signal Attenuation

The weakening of a signal as it travels through a cable. Larger diameter coaxial cable results in less signal attenuation.

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Aircraft Stress Frequency

A specific frequency (121.5 MHz) that is used for emergency communications in aviation and can be picked up by some CATV channels.

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Midband Channel

A specific range of frequencies used for CATV services, susceptible to interference from radiation, especially channels that include the aircraft stress frequency (121.5 MHz).

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Signal-to-Noise Ratio

The ratio of desired signal strength to the strength of unwanted noise. A higher ratio indicates a clearer signal.

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Preemphasis

A technique used to boost high-frequency components of a signal before transmission, improving signal clarity.

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Deemphasis

A technique used to reduce the strength of high-frequency components of a signal after reception, improving signal quality.

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Fiber Optic Cable

A cable made of thin glass fibers that transmit light signals over long distances with minimal loss.

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Amplitude Modulation (Light)

Varying the intensity of light to encode information for transmission over fiber optic cables.

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Photoelectric Detector

A device that converts light signals back into electrical signals at the receiving end of a fiber optic cable.

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Internal Reflection

The phenomenon where light bounces back inside a material, such as a fiber optic cable, due to its reflective surface.

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Refraction

The bending of light as it passes from one medium to another, due to a change in the speed of light.

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Directional Coupler

A three-terminal device that samples a signal from a trunk line without affecting the main signal flow. It uses a loop to capture the signal and a resistor to absorb reflected energy.

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What does a directional coupler use to sample the signal?

A directional coupler uses a loop, which acts as both a capacitor and an inductor, to tap off a sample of the signal from the trunk line.

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What is the purpose of the 75-ohm resistor in a directional coupler?

The 75-ohm resistor terminates the loop and absorbs reflected energy, ensuring that the directional coupler only samples the forward signal and not reflections.

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Insertion Loss

The attenuation of a signal as it passes through a device, such as a directional coupler or line tap.

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Tap Loss

The attenuation of a signal when it is tapped off from the main line, as in a directional coupler or line tap.

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Bridging Amplifier

An amplifier used to compensate for the tap loss in directional couplers and line taps, restoring the signal strength.

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Line Tap

A device that branches off a signal to a subscriber's drop line, similar to a directional coupler but specifically designed for residential connections.

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Isolation in Cable Systems

Minimizing interference between subscriber lines by using high tap-to-tap loss in line taps. This prevents a mismatched load on one line from affecting other lines.

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Index of Refraction (n)

A measure of how much light bends when passing from one medium to another. It's calculated by dividing the speed of light in a vacuum by the speed of light in the medium.

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Critical Angle

The angle of incidence at which light is totally reflected within a medium, rather than passing out into another medium.

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Acceptance Angle

The maximum angle at which light can enter an optical fiber and still be guided through it by internal reflections.

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Modal Dispersion

The spreading out of light pulses in an optical fiber due to different paths taken by light rays, resulting in a delay in signal transmission.

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Cladding Material

A layer surrounding the core of an optical fiber, with a higher index of refraction than the core, to enhance internal reflections.

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Fine Fibers

Small-diameter fibers in optical cables, used to minimize modal dispersion and improve signal quality.

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Study Notes

Cable Television (CATV)

  • Cable television (CATV) began as a way to deliver signals to areas with weak broadcast reception, using community antennas.
  • Modern cable systems cover large geographical areas and offer more channels than broadcast television.
  • Cable systems use a converter box to allow viewers to select specific channels.
  • Premium pay services often offer movies and sports programming not available on broadcast television.

Cable Frequencies

  • Older cable systems often use VHF channels for broadcast signals, converting UHF channels to VHF for distribution since UHF losses are high in cable.
  • 12-channel systems include lowband and highband VHF channels (2-13).
  • No converter is needed for such systems. Cable signals are directly connected to the TV.
  • Adjacent channels may interfere, with interference reduced by a consistent signal level for each channel across the system.
  • Midband and superband channels operate in frequency bands between VHF channels, allowing use of frequencies not assigned to broadcasting, minimizing interference.

Cable Channel Numbers and Frequencies

  • Cable TV channels use numbers 14 and higher, or letter designations, for midband channels (typically in the range of 88 to 174 MHz).
  • This range encompasses the FM radio band (88-108 MHz) but usually is not used for TV signals.
  • Superband cable channels are above VHF channel 13. Numbered or lettered, from J or 23 through 53.
  • Higher frequencies require more sophisticated cable and amplifiers due to signal loss.

Cable Connections and Tuning

  • Cable systems use a separate converter to tune to cable channels, as receivers typically are not designed to select cable channels.
  • The converter changes all cable frequencies to a standard VHF channel (e.g., 2, 3, or 4).
  • Converters descramble premium channels.

Cable Radiation

  • Cable systems must minimize radiation, which can occur if cables have open sections, short circuits, or mismatches.
  • Cables can be tested for radiation using a portable FM radio receiver to detect any interference.

Coaxial Cable

  • Coaxial cable is used to convey cable signals, typically a copper inner conductor surrounded by a polyethylene insulator, then a shield (aluminum with copper plating often).
  • Cable size and diameter are important for signal loss. Thicker cable has less attenuation, but it is harder to install.
  • Several types of cable for different uses in the system exist, like standard trunk cable, hollow trunk cable, and armored cable, along with armored cable for outdoor use.

Cable Amplifiers

  • Cable systems utilize amplifiers to boost signal strength over long distances, known as trunk amplifiers.
  • Bridging amplifiers distribute signals from trunk lines to individual neighborhoods.
  • Line amplifiers are used in long branch lines.
  • Cable systems incorporate a distribution system to provide signal delivery to customers across various frequencies.

Cable Signal Loss Considerations

  • Transmission losses affect cable systems since energy is dissipated in the cable itself. Losses increase proportionately with frequencies.
  • Distance between signal source and receiving point affects signal loss, and cable losses are also a function of frequency.
  • Frequency differences can affect signal strength and clarity.

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Cable Television (CATV) PDF

Description

This quiz covers the fundamentals of Cable Television (CATV), including its history, technology, and channel frequencies. Learn how cable systems operate and the various types of channels they provide, from premium pay services to traditional broadcasts.

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