Cable Television Basics Glossary
A
active tap A cable television feeder device consisting of a
directional coupler and a hybrid splitter (e.g., a conventional
subscriber tap), in addition to an amplifier circuit.
adjacent channel (1) Any two television channels spaced 6
MHz apart. (2) The channel (frequency band) immediately
above or below the channel of interest.
ambient temperature The temperature surrounding
apparatus and equipment. Synonymous with room
temperature.
amplifier Device used to increase the operating level of an
input signal. Used in a cable system's distribution plant to
compensate for the effects of attenuation caused by coaxial
cable and passive device losses.
amplitude The size or magnitude of a voltage or current
waveform; the strength of a signal.
amplitude modulation (AM) The form of modulation in
which the amplitude of the signal is varied in accordance
with the instantaneous value of the modulating signal.
amplitude modulated link (AML) A form of microwave
communications using amplitude modulation for the
transmission of television and related signals.
analog Pertaining to signals in the form of continuously
variable physical quantities.
antenna Any structure or device used to collect or radiate
electromagnetic waves.
antenna array A radiating or receiving system composed of
several spaced radiators or elements.
attenuator A device for reducing the amplitude of a signal.
audio Relating to sound or its reproduction; used in the
transmission or reception of sound.
audio frequency A frequency lying within the audible
spectrum (the band of frequencies extending from about 20
Hz to 20 kHz).
aural carrier The carrier that has the audio portion of a
television channel. A television channel usually contains
both a visual and an aural carrier. An aural carrier is
sometimes referred to as a sound carrier.
aural center frequency (1)The average frequency of an
emitted signal when modulated by an aural (audio) signal.
(2) The frequency of the emitted wave without modulation.
Usually refers to frequency modulation methods.
automatic tilt Automatic correction of changes in tilt, or the
relative level of signals of different frequencies.
B
bandwidth (1) A measure of the information carrying
capacity of a communication channel. The bandwidth
corresponds to the difference between the lowest and highest
frequency signal that can be carried by the channel. (2) The
range of usable frequencies that can be carried by a cable
television system.
black level That level of picture signal corresponding to the
maximum limit of black peaks.
bridging amplifier An amplifier connected directly into the
main trunk of the cable television system. It serves as a
sophisticated tap, providing isolation from the main trunk,
and has multiple high-level outputs that provide signals to
the feeder portion of the distribution network. Synonymous
with bridger and distribution amplifier.
broadband Any system able to deliver multiple channels
and/or services to its users or subscribers. Generally refers to
cable television systems. Synonymous with wideband.
C
cable television A broadband communications technology
in which multiple television channels as well as audio and
data signals are transmitted either one way or bidirectionally
through a distribution system to single or multiple specified
locations. The term also encompasses the associated and
evolving programming and information resources that have
been and are being developed at the local, regional, and
national levels.
cable television relay station (CARS) A fixed or mobile
microwave communications station used for the
transmission of television and related audio signals, FM
broadcast stations, cablecasting, data or other information,
or test signals for reception at one or more fixed receiving
points from which the signals are then distributed to the
public by cable.
cable television system A broadband communications
system capable of delivering multiple channels of
entertainment programming and non-entertainment
information from a set of centralized antennas, generally by
coaxial cable, to a community. Many cable television
designs integrate microwave and satellite links into their
overall design, and some now include optical fibers as well.
Often referred to as cable television, which usually stands
for community antenna television system.
carrier An electromagnetic wave of which some
characteristic is varied in order to convey information.
carrier-to-noise ratio The ratio of amplitude of the carrier
to the noise power relative to a 4 MHz bandwidth in the
portion of the spectrum occupied by the carrier. Also
referred to as the C/N ratio, or C/N.
CATV Abbreviation for community antenna television or
cable television system. A cable television system is a
broadband communications system that provides multiple
channels from centralized antennas.
Cable Television Basics Glossary
Page 1
certificate of compliance Authorization issued by the FCC
for the operation of a cable television system in a
community or for the carriage of additional television
signals by an operating cable television system.
channel A signal path of specified bandwidth for conveying
information.
channel capacity In a cable television system, the number
of channels that can be simultaneously carried on the
system. Generally defined in terms of the number of 6 MHz
(television bandwidth) channels for NTSC.
channel frequency response (1) The relationship within a
cable television channel between amplitude and frequency of
a constant amplitude input signal as measured at a
subscriber terminal. (2) The measure of amplitude frequency
distortion within a specified bandwidth.
co-channel interference Interference on a channel caused
by another signal operating on the same channel.
coaxial cable A type of cable used for broadband data and
cable systems. Composed of a center conductor, insulating
dielectric, conductive shield, and optional protective
covering, this type of cable has excellent broadband
frequency characteristics, noise immunity, and physical
durability. Synonymous with coax.
Community Antenna Television System See CATV.
composite The effect of several distortion signals present
within a very narrow bandwidth. See discrete.
composite second-order beat (CSO) (1) A clustering of
second order beats 1.25 MHz above and below the visual
carriers in cable systems. (2) A ratio, expressed in decibels,
of the peak level of the visual carrier to the peak of the
average level of the cluster of second-order distortion
products located 1.25 MHz above the visual carrier.
composite triple beat (CTB) (1) A clustering of third-order
distortion products around the visual carriers in cable
systems. (2) A ratio, expressed in decibels, of the peak level
of the visual carrier to the peak of the average level of the
cluster of third-order distortion products centered around the
visual carrier.
continuous sweep mode The spectrum analyzer condition
where traces are automatically updated each time trigger
conditions are met.
converter Also known as processor. Device for changing
the frequency of a television signal. A cable head end
converter changes signals from frequencies at which they
are broadcast to clear channels that are available on the
cable distribution system. A set-top converter is added in
front of a subscriber's television receiver to change the
frequency of the midband, superband, or hyperband signals
to a suitable channel or channels (typically a low- VHF
channel) which the television receiver is able to tune.
cross modulation A form of television signal distortion
where modulation from one or more television channels is
imposed on another channel or channels.
CSO See composite second-order beat.
CTB See composite triple beat.
D
dB See decibel.
dBc Decibel carrier. A ratio expressed in decibels that refers
to the gain or loss relative to a reference carrier level.
dBm See decibel milliwatt.
dBmV See decibel millivolt.
decibel (dB) A unit that expresses the ratio of two power
levels on a logarithmic scale.
decibel millivolt (dBmV) A unit of measurement referenced
to one millivolt across a specified impedance (75 ohms in
cable television).
decibel milliwatt (dBm) A unit of measurement referenced
to one milliwatt across a specified impedance.
decibels In spectrum analyzer operation, a general term
used to denote a decrease of signal magnitude in
transmission from one point to another. Attenuation may be
expressed as a scalar ratio of the input to the output
magnitude in decibels.
demodulate To retrieve an information- carrying signal
from a modulated carrier.
demodulator A device that removes the modulation from a
carrier signal.
distortion An undesired change in waveform of a signal in
the course of its passage through a transmission system.
distribution amplifier See bridging amplifier.
distribution system The part of a cable television system
consisting of trunk and feeder cables that are used to carry
signals from the system head end to subscriber terminals.
Often applied, more narrowly, to the part of a cable
television system starting at the bridger, amplifiers.
Synonymous with trunk and feeder system.
drift A change in the output of a circuit that occurs slowly.
E
electromagnetic interference Any electromagnetic energy,
natural or man-made, which may adversely affect
performance of the system.
electromagnetic spectrum The frequency range of
electromagnetic radiation that includes radio waves, light
and X-rays. At the low frequency end are subaudible
frequencies (i.e., 10 Hz) and at the other end, extremely
high frequencies (e.g., X-rays, cosmic rays).
Cable Television Basics Glossary
Page 2
F
fiber optics The technology of guiding and projecting light
for use as a communications medium. Hair-thin glass fibers
that allow light beams to be bent and reflected with low
levels of loss and interferences are known as "glass optical
wave guides" or simply "optical fibers."
field One-half of a complete picture (or frame) interval,
containing all of the odd or even scanning lines of the
picture.
field frequency The rate at which a complete field is
scanned, nominally 60 times per second for NTSC
monochrome video signals, and 59.94 times per second for
NTSC color video signals .
field strength The intensity of an electromagnetic field at a
given point, usually referred to in microvolts per meter.
field strength meter (FSM) A frequency selective
heterodyne receiver capable of tuning to the frequency band
of interest; in cable television, 5 to 750 MHz and above with
indicating meter showing the magnitude input of voltage
and a dial indicating the approximate frequency.
Synonymous with signal level meter.
FM modulator In cable television, a device similar to an
FM transmitter that is used to cablecast signals in the FM
band on a cable system.
frame One complete picture consisting of two fields of
interlaced scanning lines.
frequency band splitter/mixer A device similar to other
splitters except that it provides branching on a frequency
division basis.
frequency modulation (FM) A form of modulation in
which the frequency of the carrier is varied in accordance
with the instantaneous value of the modulating signal.
frequency response The peak-to-peak variation in the
displayed signal amplitude over a specified center frequency
range. Frequency response is typically specified in terms of
±dB relative to the value midway between the extremes. It
also may be specified relative to the calibrator signal.
H
harmonic distortion (1) The generation of harmonics by
the circuit or device with which the signal is processed. (2)
Unwanted harmonic components of a signal .
harmonically related carriers Harmonically related
carriers (HRC) is a tune configuration where each video
carrier is a multiple of 6 MHz. This configuration masks
composite triple-beat distortion by zero-beating the
composite triple-beat distortion with the video carriers.
head end The control center of a cable television system,
where incoming signals are amplified, converted, processed,
and combined into a common cable, along with any
origination cablecasting, for transmission to subscribers.
System usually includes antennas, preamplifiers, frequency
converters, demodulators, modulators, processors, and other
related equipment.
herringbone An interference pattern in a television picture,
appearing as either moving or stationary rows of parallel
diagonal or sloping lines superimposed on the picture
information.
hertz (Hz) A unit of frequency equivalent to one cycle per
second.
heterodyne processor An electronic device used in cable
head ends that down-converts an incoming signal to an
intermediate frequency for filtering, signal level control, and
other processing, and then reconverts that signal to a desired
output frequency.
HRC See harmonically related carriers.
hub A point in the distribution system used to redistribute
signals from the head end. Usually the hub is fed the cable
broadband signals by a fiber optic or CARS band link.
hum modulation Undesired modulation of the television
visual carrier by power-line frequencies or their harmonics
(e.g., 60 or 120 Hz), or other low-frequency disturbances.
Hz See hertz.
I
impedance The combined effect of resistance, inductive
reactance, and capacitive reactance on a signal at a
particular frequency. In cable television, the nominal
impedance of the cable and components is 75-ohms.
incremental coherent carriers (ICC/IRC) A cable plan in
which all channels except 5 and 6 correspond with the
standard channel plan. The technique is used to reduce
composite triple-beat distortions. Synonymous with
incrementally related carriers.
incrementally related carriers Incrementally related
carriers (IRC) is a tune configuration where all channels
except channels 5 and 6 are standard channels (see
standard tune configuration for a definition of standard
channels).
ingress The unwanted leakage of interfering signals into a
cable television system.
insertion test signals See vertical interval reference test
signal.
IRC See incrementally related carriers.
L
leakage Undesired emission of signals out of a cable
television system, generally through cracks in the cable,
corroded or loose connections, or loose device closures.
Synonymous with signal leakage.
Cable Television Basics Glossary
Page 3
line extender Feeder line amplifiers used to boost signal
and thereby extend the useful range of the feeder cable.
line frequency (1) The number of times per second that the
scanning spot crosses a fixed vertical line in one direction.
(2) Related to commercial power line frequency, i.e., 60 Hz.
(3) The horizontal scanning rate of a video signal. For
NTSC video, 15.734 kHz.
low noise amplifier (LNA) A low noise signal booster used
to amplify the weak signals received on a satellite antenna.
low noise block converter A combination device used on
satellite antennas that includes both a low noise amplifier
(LNA) to boost the weak signals, and a block downconverter
to convert the incoming satellite signals to a lower band of
frequencies (e.g., 70-1450 MHz).
low-frequency interference Interference effects that occur
at low frequency, generally considered as any frequency
below 15.734 kHz.
M
main trunk The major cable link or "backbone" from the
headend to a community or between communities.
matching transformer An impedance matching device
which converts the 75-ohm impedance of the subscriber
drop to the 300- ohm impedance of a television or FM
receiver.
megahertz (MHz) One million cycles per second.
microsecond One millionth of a second.
microwave A very short wavelength electromagnetic wave,
generally above 1000 MHz.
modulate To vary the amplitude, frequency, or phase of a
carrier or signal in accordance with the instantaneous
amplitude and/or frequency changes of the modulating
intelligence.
modulation The process whereby original information can
be translated and transferred from one medium to another.
Information originally carried as a variation in a particular
property (such as amplitude) of one process is transferred
and carried as a corresponding variation in some possible
different property (such as duration) of the new process.
N
narrow band A relative term referring to a system that
carries a narrow- frequency range (sometimes used to refer
to frequency bandwidths below 1 MHz). In a
telephone/television context, telephone would be considered
narrow band (3 kHz) and television would be considered
broadband (6 MHz).
National Cable Television Association (NCTA)
Washington, D.C.-based trade association for the cable
television industry; members are cable television system
operators; associate members include cable hardware and
program suppliers and distributors, law and brokerage
firms, and financial institutions. NCTA represents the cable
television industry before state and federal policy makers
and legislators. Name was changed in 1969 from National
Community Television Association.
NCTA See National Cable Television Association.
noise Random burst of electrical energy or interference
which may produce a "salt-and-pepper" pattern over a
television picture. Heavy noise is sometimes called "snow."
noise factor Ratio of input signal-to-noise ratio to output
signal-to-noise ratio.
noise figure The amount of noise added by signal-handling
equipment (e.g., an amplifier) to the noise existing at its
input, usually expressed in decibels.
noise temperature The temperature that corresponds to a
given noise level from all sources, including thermal noise,
source noise, and induced noise.
NTSC video signal A 525-line color-video signal whose
frequency spectrum extends from 30 Hz to 4.2 MHz. NTSC
video consists of 525 interlaced lines, with a horizontal
scanning rate of 15,734 Hz, and a vertical (field) rate of
59.94 Hz. A color subcarrier at 3.579545 MHz contains
color hue (phase) and saturation (amplitude) information .
O
off-the-air tune configuration The tune configuration for
signals that are broadcast over the air and received with an
antenna.
P
passive device A device basically static in operation; that is,
it is not capable of amplification or oscillation, and requires
no power for its intended function. Examples include
splitters, directional couplers, taps, and attenuators.
performance standards Certain minimum technical
requirements, established by the appropriate regulatory
body, which must be met by a cable system operator.
pilot subcarrier A subcarrier serving as a control signal for
use in the reception of stereophonic broadcasts.
pilot carrier Signals on cable television systems used to
operate attenuation (gain) and frequency response (slope)
compensating circuitry in amplifiers.
plant (slang) The head end and distribution hardware of a
cable television system.
R
radiofrequency (RF) An electromagnetic signal above the
audio and below the infrared frequencies.
resolution (horizontal) The amount of resolvable detail in
the horizontal direction in a picture. It is usually expressed
Cable Television Basics Glossary
Page 4
as the number of distinct vertical lines, alternately black and
white, that can be seen in three-quarters of the width of the
picture. This information usually is derived by observation
of the vertical edge of a test pattern. A picture that is sharp
and clear and shows small details has good, or high,
resolution. If the picture is soft and blurred and small details
are indistinct, it has poor, or low, resolution. Horizontal
resolution depends upon the high-frequency amplitude and
phase response of the pickup equipment, the transmission
medium, and the picture monitor, as well as on the size of
the scanning spots.
resolution (vertical) The amount of resolvable detail in the
vertical direction in a picture. It is usually expressed as the
number of distinct horizontal lines, alternately black and
white, that can be seen in a test pattern. Vertical resolution
is primarily fixed by the number of horizontal scanning
lines per frame. Beyond this, vertical resolution depends on
the size and shape of the scanning spots of the pickup
equipment and picture monitor and does not depend upon
the high-frequency response or bandwidth of the
transmission medium or picture monitor.
response time The time interval between the instant a
signal or stimulus is applied to or removed from a device or
circuit, and the instant the circuit or device responds or acts.
ride out (slang) Making a customer or equipment service
call or measurement session at a tap somewhere in the
distribution system.
S
scrambled To alter an electronic signal so that a decoding
device is necessary to receive the signal.
second harmonic In a complex wave, a signal component
whose frequency is twice the fundamental, or original,
frequency.
second-order beat Even-order distortion product created by
two signals mixing or beating against each other.
sidebands Additional frequencies generated by the
modulation process, which are related to the modulating
signal and contain the modulating intelligence.
signal level meter (SLM) See field strength meter.
signal leakage See leakage.
signal level Amplitude of signal voltage measured across
75-ohms, usually expressed in decibel millivolts.
signal-to-noise ratio The ratio, expressed in decibels, of the
peak voltage of the signal of interest to the
root-mean-square voltage of the noise in that signal.
splitter Usually a hybrid device, consisting of a
radiofrequency transformer, capacitors, and resistors, that
divides the signal power from an input cable equally
between two or more output cables.
spurious signals Any undesired signals such as images,
harmonics, and beats.
standard tune configuration The tune configuration in
which the channels are at the frequencies that the Electronic
Industries Association (EIA) and FCC define to be the
standard channel frequencies.
STD See standard tune configuration.
subcarrier A carrier used to modulate information upon
another carrier, for example, the difference channel
subcarrier in an FM stereo transmission.
suckout (1) The result of the coaxial cable's center
conductor, and sometimes the entire cable, being pulled out
of a connector because of contraction of the cable. (2) A
sharp reduction of the amplitude of a relatively narrow
group of frequencies within the cable system's overall
frequency response.
sync generator An electronic device that supplies common
synchronizing signals to a system of several video cameras,
switchers, and other video production equipment, ensuring
that all will be "locked" to a master timing reference.
sync level The level of the tips of the synchronizing pulses,
usually 40 IRE units from blanking to sync tip.
synchronization The maintenance of, one operation in
frequency and/or in phase with another.
synchronization pulse A transmitted pulse that is used to
synchronize the electron beam of a picture monitor with the
scanning device of the transmission source.
synchronous For transmission, operation of the sending and
receiving instruments continuously at the same frequency .
system noise That combination of undesired and fluctuating
disturbances within a cable television channel that degrades
the transmission of the desired signal.
system impedance The resistance and reactance opposing
the current flow in the system. For cable television the
impedance is 75 ohms. See also impedance.
T
television channel The range or band of the radiofrequency
spectrum assigned to a television station. In Canada and the
United States, the standard bandwidth is 6 MHz.
terminal isolation The attenuation, at any subscriber
terminal, between that terminal and any other subscriber
terminal in the cable television system.
third harmonic In a complex wave, a signal component
whose frequency is three times the fundamental, or original,
frequency.
third-order beat See triple beat.
tilt compensation The action of adjusting, manually or
automatically, amplifier frequency/gain response to
Cable Television Basics Glossary
Page 5
compensate for different cable length frequency/attenuation
characteristics.
trap (1) A passive device used to block a channel or
channels from being received by a cable television
subscriber (negative trap), or used to remove an interfering
carrier from a channel that a subscriber wants to receive
(positive trap). (2) An unprogrammed, conditional jump to a
specified address that is automatically activated by
hardware, a recording being made of the location from
which the jump occurred.
triple beat Odd order distortion products created by three
signals, mixing or beating against each other, whose
frequencies fall at the algebraic sums of the original
frequencies. Synonymous with third-order beat.
truck roll (slang) Using a cable television company vehicle
to make a service call.
trunk amplifier An amplifier inserted into a trunk line. A
weak input signal is amplified before being retransmitted to
an output line, usually carrying a number of video voice or
data channels simultaneously. Amplifiers increase the range
of a system. Usually, trunk amplifiers must be inserted
approximately every 1,500 to 2,000 feet.
trunk The main distribution lines leading from the head
end of the cable television system to the various areas where
feeder lines are attached to distribute signals to subscribers.
tune configuration Refers to the correlation between the
channel numbers and the frequency to which a channel is
assigned. For example, the frequency at which channel 1 is
broadcast differs between the HRC and IRC tune
configurations.
U
units Dimensions on the measured quantities. Units usually
refer to amplitude quantities because they can be changed.
In spectrum analyzers with microprocessors, available units
are dBm (dB relative to 1 mW dissipated in the nominal
input impedance of the spectrum analyzer), dBmV (dB
relative to 1 mV), dBV (dB relative to 1 V), volts, and, in
some spectrum analyzers, watts.
unscrambled A signal that has not been scrambled. An
unscrambled signal does not need a decoder to receive the
signal correctly.
V
vertical interval test signal (VITS) A signal that may be
included during the vertical blanking interval to permit
in-service testing and adjustment of video transmission.
vestigial sideband Amplitude modulation in which the
higher frequencies of the lower sideband are not
transmitted. At lower baseband frequencies, the carrier
envelope is the same as that for normal double-sideband
AM.
video A term pertaining to the bandwidth and spectrum of
the signal that results from television scanning and that is
used to reproduce a picture. In spectrum analyzer operation,
a term describing the output of a spectrum analyzer's
envelope detector. The frequency range extends from 0 Hz
to a frequency that is typically well beyond the widest
resolution bandwidth available in the spectrum analyzer.
However, the ultimate bandwidth of the video chain is
determined by the setting of the video filter. Video is also a
term describing the television signal composed of a visual
and aural carriers.
video average The digital averaging of spectrum analyzer
trace information. It is available only on spectrum analyzers
with digital displays.
video bandwidth (1) The maximum rate at which dots of
illumination are displayed on a screen. (2) The occupied
bandwidth of a video signal. For NTSC, that bandwidth is
4.2 MHz.
visual signal level The peak voltage produced by the visual
signal during the transmission of synchronizing pulses.
visual carrier The visual carrier is the portion of a
television signal that contains the picture. A television
signal contains both a visual and an aural carrier.
visual carrier frequency The frequency of the carrier that
is modulated by the picture information, which is 1.25 MHz
above the bottom end of a television channel.
W
waveform monitor A special-purpose oscilloscope which
presents a graphic illustration of the video and sync signals,
amplitude, and other information used to monitor and adjust
baseband video signals.
white level The level of a visual carrier that corresponds to
the maximum level of the white area for a picture signal.
windshield wiper effect Onset of overload in multichannel
cable television systems caused by cross modulation; the
horizontal sync pulses of one or more television channels
are superimposed on the desired channel carrier. The visual
effect of the interference resembles a diagonal bar wiping
through the picture.
Cable Television Basics Glossary
Page 6
Tidak ada komentar:
Posting Komentar