60 Cycle Hum

These hum bars at 60 cycles are normally a result of dc power on the line. See dcBlocker.

A/B Switch

A switch that selects one of two inputs (A or B) for routing to a common output while providing adequate isolation between the two signals.

Adjacent Channel

An adjacent channel is one which is immediately next to another channel.

AFC

A circuit which locks an electronic component onto a chosen frequency.

AGC

Controlling the gain of a device by the signal level through the device (using a high gain feedback loop circuit). A rising input signal level produces a negative feedback signal, which lowers the gain. A circuit that uses feedback to maintain the output of an electronic component at a constant level.

Agile Component

A component which can be tuned to any desired channel.

Amplifier

A device used to increase the power of a signal.

Analog

A system in which signals vary continuously in contrast to a digital system in which signals vary in discrete steps.

Antenna

A device that contributes an energy gain. Satellite dishes, broadband antenna and cut-to-channel antennas are some types of antennas encountered in private cable systems.

Antenna Pre-Amplifier

An amplifier located in the immediate vicinity of the antenna, used to amplify extremely weak signals, thereby improving the signal-to-noise ratio of a system.

Attenuation

The decrease in signal power that occurs in a device or when a signal travels to reach a destination point (path loss).

Attenuator

A passive electronic device to reduce signal strength by a specified amount (usually expressed in dB). A passive device which reduces the power of a signal. Attenuators are rated according to the amount of signal attenuation.

Audio Subcarrier

The carrier wave that transmits audio information within a video broadcast signal. Satellite transmissions can relay more than a single audio subcarrier in the frequency range between 5 and 8.5 MHz.

Automatic Brightness Control

A television circuit used to automatically adjust picture tube brightness in response to changes in background or ambient light.

Automatic Fine Tuning

A circuit that automatically maintains the correct tuner oscillator frequency and compensates for drift and for moderate amounts of inaccurate tuning. Similar to AFC.

Automatic Frequency Control

A circuit that locks onto a chosen frequency and will not drift away from that frequency.

Automatic Gain Control

A circuit that locks the gain onto a fixed value and thus compensates for varying input signal levels keeping the output constant.

Band

A range of frequencies.

Band Separator

A device used to split 2 or more frequency bands into separate leads.

Bandpass Filter

A circuit or device that allows only a specified range of frequencies to pass from input to output.

Bandwidth

The frequency range allocated to any communication circuit.

Baseband

A signal without a carrier. A television camera produces baseband signals. Television monitors which accept baseband signals do not require an R.F. tuner or an I. F. detector section. Baseband audio is pure audio as from a tape recorder. Baseband video contains no audio information. For basebands to be used by a normal television, it must be modulated at the frequency of the particular channel into which it is to be fed.

BNC Connector

A weatherproof twist lock coax connector standard on commercial video equipment and used on some brands of satellite receivers.

Boresight

The direction along the principle axis of either a transmitting or a receiving antenna.

Broadband

A device that processes a signal (s) spanning a relatively broad range of input frequencies.

Cable-Ready Television

A television receiver that can receive unscrambled cable television channels without the use of a converter.

Carrier

A pure-frequency signal that is modulated to carry information. In the process of modulation it is spread out over a wider band. The carrier frequency is the center frequency on any television channel.

CATV

An abbreviation for Community Antenna Television- another name for cable TV.

CCD

Charge coupled device. In this device charge is stored on a capacitor which are etched onto a chip. A number of samples can be simultaneously stored. Used in MAC transmissions for temporarily storing video signals.

Channel

A segment of bandwidth used for one complete communication link.

Clipping

The shearing off of the peaks of a signal. For a picture signal, this may affect either the positive (white) or negative (black) peaks. For a composite video signal, the synchronizing signal may be affected.

Coaxial Cable

The most commonly used means of signal distribution, consisting of a center conductor and a cylindrical outer conductor (shield). A cable for transmitting high frequency electrical signals with low loss. It is composed of an internal conducting wire surrounded by an insulating dielectric which is further protected by a metal shield. The impedance of coax is a product of the radius of the central conductor, the radius of the shield and the dielectric constant of the insulation. In an SMATV system, coax impedance is 75 ohms.

Color Bar

A test signal, typically containing six, basic colors: yellow, cyan, green, magenta, red, and blue, which is used to check the chrominance functions of color TV systems.

Combiner

An active or passive device that serves to combine several signals into one output while maintaining a high degree of isolation between each input.

Composite Baseband Signal

The complete audio and video signal without a carrier wave. Satellite signals have audio baseband information ranging in frequency from zero to 3400 Hertz. NTSC video baseband is from zero to 4.2 MHz . PAL video baseband ranges from 0 to 5.5 MHz.

Composite Video Signal

The complete video signal consisting of the chrominance and luminance information as well as all sync and blanking pulses.

Contrast

The ratio between the dark and light areas of a television picture.

Converter

A device for changing signals from one frequency to another frequency. A device used to transfer signals from a channel of one frequency to another.

Cross Modulation

A form of distortion where modulation of an interfering stating appears a modulation of the desired station. A form of interference caused by the modulation of one carrier affecting that of another signal. It can be overloading an amplifier as well as by signal imbalances at the headend.

Cross Talk

Interference between adjacent channels often caused by cross modulation. Leakage can occur between two wires, PCB tracks or parallel cables.

dc Power Block

A device which stops the flow of dc power but permits passage of higher frequency ac signals.

De-Emphasis

The restoration of a pre-emphasized signal wave to its original form (see Pre-Emphasis).

Decibel (dB)

A logarithmic function used to simplify CTN calculations. Decibels may be added or subtracted. 0 dB is the standard reference level for all CTN calculations. The logarithimic ratio of power levels used to indicate gains or losses of signals. Decibels relative to one watt, milliwatt and millivolt are abbreviated as dBm V is used as the standard reference for all SMATV calculations.

Decoder

A circuit that restores a signal to its original form after it has been scrambled.

Demodulator

A device which detects ths signal from the carrier, usually the I.F. frequency. It eliminates the carrier from signal, retaining the intelligence portion (video, audio or data) for further processing. A device which extracts the baseband signal from the transmitted carrier wave.

Detent Tuning

Tuning into a channel by selecting a preset resistance.

Dielectric

An electrical insulator in which the electrical field can by sustained with a minimum dissipation of its energy.

Digital

Describes a system or device in which information is transferred by electrical “on-off�, “high- low�, or “1/0� pulses instead of continuously varying signals or states as in an analog message.

Digital-to-Analog Converter

A circuit that converts digital signals into their equivalent analog form.

Diplexer

A device that combines RF frequencies (not power assigned) and satellite frequencies (power assigned) on to one coax. Diplexers can also separate satellite and RF signals.

Discrete Stereo

A method of transmitting stereo in which the left and right channels are contained on completely separate subcarriers. To tune in this type of stereo, two completely separate subcarrier tuners are needed. The demodulator side of the deviation from a standard center frequency, the tuning frequency of the F.M. signal.

Distribution System

A system consisting of coax that carries signals from the headend to each video location.

Drifting

An instability in a preset voltage, frequency or other electronic circuit parameter.

Drop Cable

The cable used to route a signal from outside distribution equipment to a television.

Echo

A signal which has been reflected at one or more points during transmission with sufficient magnitude and time difference as to by detected as a signal distinct from that of the primary signal. Echoes can be either leading or lagging the primary signal and appear as reflection, or “ghosts� in an AM system.

Egress Interference

An undesired leakage of radiation from a cable or other closed circuit system.

Encoder

A device for scrambling a signal.

F-Connector

A standard RF connector used to link coax cables with electronic devices.

FCC

The Federal Communications Commission, the regulatory board which sets standards for communication within the United States.

Feeder Line

The coaxial cable serving as a subtrunk to feed drop cables.

Filter

A device used to reject all but a specified range of frequencies. A bandpass filter allows only those signals within a given band to be communicated. A rejection filter, the mirror image of a bandpass filter, eliminates those signals within a specified band but passes all other frequencies.

Frequency

The number of vibrations per second of an electrical or electromagnetic signal expressed in cycles per second or Hertz. Frequency Response : The change of gain with frequency.

Gain

A measure of amplification, usually expressed in dB. For match CATV components, power gain is readily determined as insertion power gain. The amount of amplification of input to output power often expressed as a multiplicative factor or in decibels.

Gain Compression

The gain of any amplifier is a function of the input signal level, and will always decrease at some point where the input level is sufficiently high. The capacity of an amplifier is sometimes expressed as the level where the gain of the amplifier is decreased or compressed by a certain amount.

Ghosts

A ghost displaced to the left of the primary image is designated as “leading�, and one displaced to the right is designated as “following� (lagging). When the tonal variations of the ghost are the same as those of the primary image, it is designated as “positive� and when the reverse condition occurs, it is designated as “negative�.

GHz

A frequency designation. Giga means billion and hertz means cycles per second. 3.7Ghz would be 3,700,000,000 cycles per second. 1000 MHz or one billion cycles per second.

Ground Loop

These humbars are created when there is a substantial difference in the grounding resistance at two different points of a system. Headend : The electronic reception and distribution equipment located at the start of a cable system. The portion of a TV system where all desired signals are received and processed for subsequent distribution.

Hertz

An abbreviation for the frequency measurement of one cycle per second. Named after Heinrich Hertz, the German scientist who first described the properties of radio waves.

Hi-band

The VHF television channels. High Definition Television (HDTV) : An innovative television format having approximately twice the number of scan lines in order to improve picture resolution and viewing quality.

Horizontal (Hum) Bars

Relatively broad horizontal bars, alternately black and white, which extend over the entire picture. They may be stationary or may move up and down. Sometimes referred to as a “venetian blind� effect, it is usually caused by a 60Hz interfering frequency or a harmonic frequency.

House Drop

The coaxial cable from line tap to participants TV converter.

Hum Bars

A form of interference seen as horizontal bars or black regions passing across the field of a television screen.

I.F.

Stands for intermediate frequency. A frequency obtained by a satellite receiver after down conversion. In a dual conversion receiver there will be (2) I.F. frequencies. One is created by mixing the incoming signal with a frequency from the V.T.O. (voltage tuned oscillator). The first I.F. is usually between 500 Mhz and 1.5 Ghz. The second I.F. (70mhz) is created by mixing the first I.F. with impedance is usually 75ohms.

Insertion Loss

Additional loss in a system when a device such as a directional coupler is inserted; equal to the difference in signal level between input and output of such device. The amount of signal energy lost when a device is inserted into a communication line. Also known as “feed through� loss.

Interference

An undesired signal intercepted by frequency that causes video and/or audio distortion.

Intermodulation (Beat Frequencies)

A form of interference that is generated from creation of two or more beats between carrier. Beat frequencies are given by fbeat-nf1 + mf2 where n and m are integers.

Isolation

The amount of separation or loss (expressed in dB) between two locations or components. (Such as the loss between the feed-thru and tap/drop line of a tapoff unit).

Isolation Loss

The amount of signal energy lost between two ports of a device. An example is the loss between the feed through port and the tap/drop of a top-off device.

Isolator

A device that allows signals to pass unobstructed in one direction but which attenuates their strength in the reverse direction.

Jumper

A short piece of transmission line used to interface components in a broadcast system.

Kilohertz

One thousand cycles per second.

Level Diagram

A graphich diagram indicating the signal level at any point in a system.

Line Amplifier

An amplifier in a transmission line that boosts the strength of a signal.

Line Attentuator

A device inserted in-line of the coaxial cable to decrease the level of the signal. Attentuators come in values of 1,2,3,5,7,10,15,20,25, and 30dB.

Line Extender

Another term for Line Amplifier.

Line Splitter

A device which divides the signal symmetrically from a single cable into two or more cables of similar impedance. An active or passive device that divides a signal into two or more signals containing all the original information. A passive splitter feeds an attenuated version of the input signal to the output ports. An active splitter amplifies the input signal to overcome the splitter loss.

Lo-Band

The low VHF television channels.

Low Frequency Distortion

Distortion effects which occur at low frequency. In television, generally considered as any frequency below the 15.75 Khz line frequency (NTSC).

Low Pass Filter

An electronic circuit designed to pass all frequencies below a specified frequency while attenuating signals with frequencies above the rated value.

Master Antenna Television System (MATV)

A combination of components providing multiple television receiver operation from one antenna or group of antennas. Broadcast receiving stations that use one or more high-quality centrally located UHF and/or VHF antennas which relay their signals to many televisions in a local apartment/condo or group-housing complex.

Matching Transformer

Same as balun, generally associated with a matching device for transforming a 75 ohm coaxial cable impedance for connection to the TV set’s 300 ohm input terminal.

MegaHertz (MHz)

One million cycles per second.

Microwave

The frequency range from approximately 1 to 30 GHz and above.

Midband

Cable television channels A through 1 that lie between VHS channels 6 and 7.

Mixer

A device used to combine signals together.

Modulation

The information portion of an R.F. transmission waveform. The carrier wave is altered by the signal wave or modulated wave to produce a combined waveform, ready for transmission called an R.F. waveform or modulated signal. A process in which a message is added or encoded onto a carrier wave. Among other methods, this can be accomplished by frequency or amplitude modulation, known as AM or FM, respectively.

Modulator

A means of getting baseband frequency into an R.F. frequency that can be received by a standard TV tuner. This is accomplished by mixing the 6 Mhz (NTSC) signal with the proper carrier frequency to give a standard channel output frequency.

Monochrome

A black and white television picture. Multiplexing : The simultaneous transmission of two or more signals over a single communication channel.

Multiswitch

Combine a dual LNB output from a dish, and in some cases combine RF signals, and send signals out to multiple satellite receivers.

Noise

An unwanted signal which interferes with reception of the desired information. Noise is often expressed in degreees Kelvin or in decibels.

Noise Figure

A measure of the noisiness of an amplifier. Noise factor is defined as input signal-to-noise ratio to output signal-to-noise ratio. Noise figure is noise factor expressed in dB. The lowest possible value for a matched system is 3 dB. The ratio of the actual noise power generated at the input of an amplifier to that which would be generated in an ideal resistor. The lower the noise figure, the better the performance.

NTSC

National Television Systems Committee. An industry-wide engineering group which, during 1950-1953, developed the color television specification now established in the United States. The National Television Standards Committee which created the standard for North American TV broadcasts.

PAL(Phase Alternation Line)

A video standard used in many parts of the world. Phase Alternate Line. The European color TV format which evolved from the American NTSC standard. Passband : The band of frequencies that a circuit passes with little attentuation.

Passive

An electronic device alters or controls a signal but does not contain any transistor stage for amplification, oscillation or modulation.

Path Loss

The attenuation that a signal undergoes in traveling over a path between two points. Path loss varies inversely as the square of the distance traveled. Pay-Per-View : Pay-per-view is a method of purchasing programming on a per-program basis.

Polarization

The direction of the electric vector of the radiated signal.

Preamplifier

An amplifier, usually mast mounted, used prior to the main amplifier to increase weak signals. The preamplifier establishes the noise figure of the system. The first amplification stage. In an SMATV system, it is the amplifier mounted adjacent to an antenna to increase a weak signal prior to its processing at the headend. Radio Frequency : The approximately 10 kHz to 100 GHz electromagnetic band of frequencies used for man-made communication.

Raster

The random pattern of illumination seen on a television screen when no video signal is present.

Reference Signal

A highly stable signal used as a standard against which other variable signals may be compared and adjusted.

Repeater

A device, usually remote, which receives a signal transmitted from an external sources, amplifies this signal and retransmits it, usually at a different frequency. It enables transmitted signals to travel great distances. Communications satellites are very sophisticated repeaters. A device that receives and re-broadcasts signals to extend the range of an original broadcast facility.

Return Loss

The ratio of the total power, transferred and reflected (and also “incident� power) to the reflected power alone, when expressed in decibels, is called the return loss. The return loss expresses the relative strength of a signal traveling “backwards� through a transmission system, to that travelling in the “desired� direction. A ratio of the amount of reflected signal to the total available signal entering a device expressed in decibels.

Reverse Isolation

An amplifier is used between the antenna or cable company input and the modulator combiner to isolate the signal. This will prevent the picture produced from your modulator from leaking out to other peoples TV’s.

Roll

A loss of vertical sychronization which causes the picture to move up or down on receiver or monitor.

S.N.R. (Signal to Noise Ratio)

A ratio between desired signal and unwanted noise, expressed in decibels. This term is used extensively in broadcasting and video. The ratio of signal power to noise power in a specified bandwidth, usually expressed in decibels.

Scrambling

A method of altering the identity of a video or audio signal in order to prevent its reception by persons not having authorized decoders.

Sidebands

The signals falling in the band of frequencies on either side of a carrier resulting from the process of modulation.

Signal Strength

The intensity of the television signal measured in volts, millivolts, microvolts, or dB, using 0 dB as a reference. Equal to 1000 microvolts in RF systems; generally 1 volt in video systems.

Snow

Heavy random noise. Video noise or sparklies caused by an insufficient signal-to-noise input ratio to a television set or monitor.

Spacing

Length of a cable between amplifiers based on the amount of grain required to overcome cable losses in dB at the highest TV channel carried in a system; TX Converter Channel or (920) MHz (NTSC).

Splitter

A device that takes a signal and splits it into two or more identical but lower power signals.

Splitter or Directional Coupler

A device having one input and providing two or more isolated outlets for RF cable runs.

Streaking

A term used to describe a picture condition in which objects appear to be extended horizontally beyond their normal boundaries.

Sub-Low Channels

TV channels between 5 MHz and 54 MHz(NTSC).

Subcarrier

A carrier superimposed on the original carrier. Subcarriers are used in satellite television to carry additional information such as the audio or color. Subcarriers for audio can be from 4.5 Mhz to 8.0 Mhz. The audio is used to modulate a carrier which is to be the subcarrier frequency. The modulated subcarrier is then combined with the video information and possibly other subcarriers to become the information waveform used to modulate the main channel carrier. A satellite receiver demodulates the signal to produce the composite video signal which contains the video information and subcarriers and then the demodulates it again, tuned to the subcarriers, to extract the subcarrier information, in this case the audio. A signal that is transmitted within the bandwidth of a stronger signal. In satellite transmissions a 6.8 MHz audio subcarrier is often used to modulate the C-band carrier. In television, a 3.58 MHz subcarrier modulates the video carrier on each channel.

Sync

An abbreviation for the words, “synchronization�, “synchronizing�, etc. Applies to the synchronization signals, or timing pulses, which lock the electron beam of the picture monitors in step, both horizontally and vertically, with the electron beam of the pickup tube. That portion of a composite picture signal which is more negative than the voltage representing the blanking level across the output of the picture line amplifier. The color sync signal (NTSC) is known as the color burst.

Synchronizing Pulses

Pulses imposed on the composite baseband video signal used to keep the television picture scanning in perfect step with the scanning at the television camera.

Tap

Any device used to obtain signal voltages from coaxial cable. The earlier forms such as capacitive and transformer taps have been replaced by directional couplers in modern systems. A device that channels a specific amount of energy out of the main distribution system to a secondary outlet.

Tearing

A term used to describe a picture condition in which groups of horizontal lines are displayed in an irregular manner.

Television Channel

A band of frequencies wide in the broadcast band and designated either by number or by the extreme lower and upper frequencies.

Termination

A term used in reference to impedance matching the end of cable runs by installing a non- inductive resistor having the same resistance value as the characteristic impedance value of the cable.

Tilt

The slope, or change, in cable attenuation or amplifier gain. The uneven attenuation of a broadband signal as it travels through coaxial cable. In general, attenuation increases as signal frequency increases.

Trap

A selective circuit used to attenuate an undesired frequency band without affecting the desired signals. An electronic device that attenuates a selected band of frequencies in a signal. Also known as a notch filter.

UHF (Ultra High Frequency)

In television a term used to designate channels 14 through 83 (NTSC). The TX Converter operates in this band. Ultrahigh frequencies ranging from 300 to 3,000 MHz. North American TV channels 14 through 83. European TV channels 21 to 69.

VHF

Very high frequencies in the range from 54 MHz to 216 MHz NTSC TV channels 2 through 13.

Video Signal

That portion of the transmitted television signal containing the picture information. Video Monitor : A television that accepts unmodulated baseband signals to reproduce a broadcast.