| |
|
|
 |
 |
 |
| ADC |
Analogue Digital Converter; converts analogue signals into digital input. |
| A.G.C. |
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. |
| 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. |
| 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 n 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. |
|
| B Channel |
Channel for transmission of ISDN user-data with a transmission speed of 64kbit/s. |
| B Frame |
Bi-directional Frame - this type of frame is produced in MPEG encoding, and can only be encoded if the previous and following frames are also known. |
| Band Separator: |
A device used to split 2 or more frequency bands into separate leads. |
| Band: |
A range of frequencies. |
| 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. |
| Base connection |
ISDN connection with SO interface which consists of 2 data channels (B channels) with 64Kbps and a data channel (D channel) with 16 Kbps. |
| 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. |
| BISYNC |
Binary Synchronous Communication - a transmission protocol for synchronous (binary) data transmission. |
| 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. |
| BRI |
Basic Rate Interface - the international term for the basic ISDN connection. |
| Bridge |
Connection between two or more networks. Can only be networks with the same topology (e.g. Ethernet) and the same protocols. |
|
| Cable-Ready Television: |
A television receiver that can receive unscrambled cable television channels without the use of a converter. |
| Cache |
Buffer memory which can be installed between different kinds of memory media. Intermediate storage in a cache reduces the access speed. |
| CAPI |
Common ISDN-API - the standardised interface for ISDN cards. |
| 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 bundling |
The combining of several B-channels which together form a virtual channel with a higher data transmission rate, especially valuable for video-conferencing and video phones. |
| Channel: |
A segment of bandwidth used for one complete communication link |
| Cinch |
Two-pin plug connection for transmission of audio and video information. |
| 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. |
| CODEC |
Coding/decoding and compression/decompression of video conferencing signals according to a particular procedure. The process has been standardised by the ITU. The conversions are done using a special CODEC card which usually includes communication interfaces (ISDN/LAN). |
| 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. |
| Continuous Presence (Quarter Split) |
A form of multipoint conference in which people in 5 locations can participate via picture and sound. With this each screen is split into 4, each sector showing a different location. |
| 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. |
| CPU-Bus |
Internal management system through which the processor exchanges data with its environment. |
| 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. |
| CVBS Signal |
A video signal including color, picture, blanking, and synchronisation information, produced by video recorders and camcorders which operate according to the Video 8 or VHS standards and in which brightness and color are transmitted in parallel. |
|
| D Channel |
In ISDN, a channel for the transmission of service information. All the relevant signals for connection and disconnection of the link are carried in the D channel. 1TR6 and DSS1 are different and non-compatible D channel protocols. |
| Data compression |
A means of increasing the effective data transmission performance. Data are compressed using special mathematical processes. |
| dc Power Block: |
A device which stops the flow of dc power but permits passage of higher frequency ac signals. |
| DCT |
Discrete Cosinus Transformation - a process for data reduction, predominantly for M-JPEG. Individual pictures are divided into blocks of 8x8 pixels and simplified colour information allocated to them. |
| DDC |
Dynamic Data Channel - is a protocol for data communication between video conferencing systems. |
| 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. |
| DECT |
Digital European Cordless Telecommunication - is the European digital transmission standard for cordless telephones. |
| De-Emphasis: |
The restoration of a pre-emphasized signal wave to its original form (see Pre-Emphasis). |
| 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. |
| Downspeeding |
A safety function which is triggered when one part of the B channels used for communication fails, and this ensures that the transmission is not completely interrupted. |
| 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. |
| DSP |
Digital Signal Processor or single chip microcomputer which is used in electronic systems to control independent processes and take on computational tasks. |
| DSS1 |
Digital Subscriber Signalling System No.1 - a signalling protocol used between the ISDN terminal devices and the PBX. |
| DSVD |
Digital Simultaneous Voice Data - a modem which supports both data transmission and voice communication at the same time. |
| DTMF |
Dual Tone Multi Frequency - dialling and controlling signals in the form of combinations of tones. |
| DVI |
Digital Video Interface - where video pictures are digitised in real time and saved as compressed video files. |
| Echo Suppression |
A system for filtering the echo feedback which occurs with speech transmission. This considerably improves the quality of the voice transmission. |
| 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. |
| Encryption/decryption |
Encryption/decryption is used to ensure that data communications cannot be eavesdropped. The encryption systems have to be installed at both transmitter and receiver sides. |
| Ethernet |
An electronic data processing network which nowadays is the most widely used system for local networks |
|
|
| FCC: |
The Federal Communications Commission, the regulatory board which sets standards for communication within the United States. |
| F-Connector: |
A standard RF connector used to link coax cables with electronic devices. |
| FDDI |
Fibre Distributed Data Interface - interface for data which is transmitted in light waves by fibre optic cable. High speed technology based on the Token ring principle. |
| 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. |
| Firewall |
A firewall seals off data networks. Any data going into or out of the network must pass through the firewall and only the data which complies with security requirements is allowed through. |
| Fixed Link |
Permanent active connection between two sub-networks within in the network. No other users can use this connection. |
| Frame |
A frame is an single picture within the body of video data. |
| Frame Rate |
With digital video this is the picture refresh rate. To achieve a full motion video a frame rate of 25 frames per second is required. With less than 15 frames per second the video movement is jerky. |
| 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. |
| Full Duplex |
refers to the ability to send and receive data simultaneously at maximum speed. |
|
| 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. |
| 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. |
| Gateway |
In video conferencing these allow H.323-compatible systems to communicate with H.32x terminals. For example a gateway system can link an H.323 system with H.320 (SIDN), H.321 (ATM), H.322 (ISO Ethernet) or H.324 (PSTN). At present an H.323 to H.323 connection (LAN/LAN) is still the most used form of VC gateway. |
| Genlock |
Generator Lock - in analogue systems this is how the video signal is fed into the PC. Using Genlock the video signal can also be blended with a graphic or with another video signal and then be put on tape. |
| 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. |
| Grabbing |
This relates to the grabbing and storage of picture data on the computer. There are various grabbing functions: screen grabbing, frame grabbing, motion grabbing. (Screenshots are individual pictures taken from the video sequence.) |
| 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. |
| GSM |
Global System for Mobile Communications - international standard for the digital mobile radio telephone network. |
|
| H.320 |
The ITU-T (International Telecommunication Union) standard for picture and sound communication over ISDN. |
| HDLC |
High-Level Data Link Control - transmission protocol |
| 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. |
| Highlight-Compression-System |
Special peripheral circuit for smear suppression and to give full detailed picture reproduction of extremely bright areas. |
| 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. |
| ICM |
Intelligent Call Management - this function dynamically distributes and manages the transmission bandwidth between video, audio and data. |
| IMUX |
Inverse Multiplexer - a device for managing transmission when using several ISDN channels for video or data communication. |
| 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. |
| Interface |
Interfaces allow the communication between different kinds of hardware and software, and between users and programs. |
| Interference: |
An undesired signal intercepted by frequency that causes video and/or audio distortion. |
| Inter-Frame Compression |
A process for compressing digital videos in which only the changes between sequential pictures are saved. - Whereas with intra-frame compression only the data within the frame is reduced. |
| 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. |
| ISDN |
Integrated Services Digital Network. |
| 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. |
| 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). |
| 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. |
|
| LAN |
Local Area Network - the networking of computers within a limited area. |
| LANC |
Local Application Control BUS System - interface for controlling video recorders and camcorders. |
| LapLINK |
A special program for data exchange between two PCs via serial or parallel ports or an ISDN card. |
| 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 Frequency Signal Level |
Low frequency signal level (linein/lineout). |
| 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. |
| MCU |
Multipoint Control Unit - a system which enables and controls a conference with more than two participants. |
| 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. |
| MIDI |
Music Instruments Digital Interface - software interface for the exchange of data between a musical instrument (keyboard etc.) and a computer. |
| Mixer: |
A device used to combine signals together. |
| MJPEG |
Motion Joint Photographic Experts Group - a digital editing compression procedure for the storage of video sequences. Whereas with MPEG (Moving Pictures Experts Group) only the differences between individual pictures are saved, here each picture is retained. |
| 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. |
| MSN |
Multiple Subscriber Number - number with many devices connected. |
| Multiplexer |
Device for recording signals from up to 16 cameras using only one video recorder. Can provide full-screen replay of individual chosen cameras as well as multi-screen displays. |
| Multiswitch: |
Combine a dual LNB output from a dish, and in some cases combine RF signals, and send signals out to multiple satellite receivers. |
|
| NDIS |
Network Driver Interface Specification - definition of interface between the local network operating system and the network adapter. |
| NetMeeting |
Microsoft NetMeeting 2.0 enables users all to benefit from audio, video, data and applications in real time over various kinds of link. The functions available vary according to the kind of connection. For connections between two modems, data and applications are supported but audio and video are not. The same is true for connections in local networks (IPX/SPX-LANs). A TCP/IP connection or a local area network (LAN) is needed to support audio and video. |
| 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. |
| Noise: |
An unwanted signal which interferes with reception of the desired information. Noise is often expressed in degreees Kelvin or in decibels. |
| NT |
Network Terminator |
| NTBC |
Network Terminal Base Connection, the connecting element between the ISDN circuit and the user connection. |
| NTSC |
National Television System Committee - the American TV standard (power supply frequency 50 Hz, 525 lines, 30 pictures/s). PAL, the European standard and SECAM, the French standard, have 625 lines and 25 pictures/s. |
| 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. |
|
| ODAPI |
Open Database Application Programming Interface - software interface controlling the data exchange between databases and other applications. |
| OSI- Layer Model |
Open Systems Interconnection (OSI) - is an ISO working group which lays down general standards. The Open Systems layer model specifies the handling and management of data transmission in a network which is divided in to different levels or layers. |
|
| PAL |
Phase Alternation Line - the European video standard (50 Hz power supply). |
| 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. |
| PBX |
Private Branch Exchange; private telecommunications exchange. |
| PCI |
Peripheral Component Interconnect - bus format for computer cards. |
| PCM |
Process Pulse Code Modulation - a process for converting analogue signals into digital information, e.g. for digitising audio data. |
| PDN |
Public Data Network. |
| Polarization: |
The direction of the electric vector of the radiated signal. |
| POTS |
Plain Old Telephone Service - analogue telephone network, using for example twisted pair cabling for modulated voice signals. |
| PPP |
Point to Point Protocol - serial transmission protocol for point to point connections, for example for access to the internet using a modem. |
| 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. |
| PSTN |
Public Switched Telephone Network - (fixed) analogue telephone network. |
|
| Quad Unit |
For simultaneous display of four camera pictures on one monitor. |
| Quality of Service |
This ensures an application is allocated specific necessary network resources in the form of a guaranteed bandwidth - an important consideration with video conferencing and voice over IP (VoIP). |
|
| Raster: |
The random pattern of illumination seen on a television screen when no video signal is present. |
| RCTC |
Timecode Rewriteable Consumer Timecode - for linear cutting in video editing. |
| Reference Signal: |
A highly stable signal used as a standard against which other variable signals may be compared and adjusted. |
| Remote Management |
Remote control of devices. |
| 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. |
| RMA Testcard |
Radio Manufacturer Association Testcard - test card or slide for testing camera quality. |
| RNA |
Remote Network Access. |
| Roll: |
A loss of vertical sychronization which causes the picture to move up or down on receiver or monitor. |
| Router |
A special device for forwarding data packages to the appropriate junctions and intersections in the network and thus linking the network together. The network topologies can be different (e.g. Token Ring and Ethernet). |
| RS232-Interface |
This is the computer connection where the mouse and the modem are plugged in. Only 9 and 25 pin connections conforming to the V.24 standard can be made with this kind of interface . |
|
| 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. |
| S/PDIF |
A digital audio interface which is connected to a digital audio device (e.g. DAT recorder) and enables copies to be made without any losses. |
| S0 Interface |
The internationally standardised interface for ISDN end-user applications. It consists of two data channels (B channels) and a signal channel (D channel). Up to eight devices with 12 ISDN sockets can be linked to the SO interface. |
| S2M Interface |
Basic ISDN connection (also primary multiplex connection) consisting of 30 user channels (B channels), one control channel (D channel) and a synch channel. Of the 32 channels, 30 are available for telephone use. (Interesting for larger firms). |
| Sampler |
A device for converting data (usually audio) into digital data. These data can then be processed in a PC. Sampling refers to the digitisation of graphics (using a graphics card) and notes, speech and sounds (using a sound card). |
| Scart |
The standard socket used in TV and video. |
| 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. |
| SCSI |
Small Computer System Interface - standardised interface for small computer systems to which peripherals (e.g. a CD drive) is connected. |
| 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 or Directional Coupler: |
A device having one input and providing two or more isolated outlets for RF cable runs. |
| Splitter: |
A device that takes a signal and splits it into two or more identical but lower power signals. |
| Streaking: |
A term used to describe a picture condition in which objects appear to be extended horizontally beyond their normal boundaries. |
| 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. |
| Sub-Low Channels: |
TV channels between 5 MHz and 54 MHz(NTSC). |
| 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. |
| TCP/IP |
Transmission Control Protocol/Internet Protocol - TCP is responsible for the correct delivery of the data packets, IP for the transportation. |
| 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. |
| TFT Display |
Thin Film Technology - the term used to describe flat screens with active internal illumination. |
| Thumbnail |
In the video editing program this is the first frame which is used to represent the video clip. |
| 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. |
| Time Multiplex Process |
Controls the transmission of different sources via a single transmission medium (serial circuit). A multiplexer allocates each source a time window in which digital data transmission is possible. |
| Token Ring |
A special data packet which is passed from station to station in a Token Ring Network. The packet can only be forwarded by the current station so that there are no collisions in the transfer of information. |
| 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. |
| V.24 |
is a control protocol for serial data transfer between a DTE (a piece of Data Terminal Equipment) and a DCE (a Distributed Computing Environment) - as between a computer and a modem. The term V.24 is often used to refer to an R232C interface. |
| VBS Signal |
The name for a video signal produced by a black & white camera. |
| VGA |
Video Graphics Array - the graphic standard used by all modern graphics cards (resolution up to 640x480 pixels). |
| 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. |
|
| W.A.V.E. |
Camera Wide Angle View Camera - camera with a particularly wide field of view (wide angle lens + camera panning radius). |
| WAN |
Wide Area Network - the networking of PCs or local networks over public or private telecommunication networks. |
| White Value Limit |
Protection system for avoiding video signals levels above >1.1 Vpp. |
| X.21 |
A transmission protocol, defining an interface in the physical layer. X.21 is used for X.25 networks. |
|
|
 |
|
 |
|
