| Fixed Cameras |
|
| Pan Tilt Zoom |
|
| Covert Cameras |
|
| Lenses |
|
| Processors | |
| ...Quads |
|
| ...Multiplexers |
|
| ...Matrix |
|
| CATV Modulators |
|
| Housing/Mounts |
|
| Power Supplies |
|
| VCRs |
|
| VHS Tape |
|
| Monitors |
|
| Wire & Coax |
|
| Tools |
|
| Uncategorized |
|
| Educational Info |
|
| Manufacturers |
|
| Installers |
|
| Bulletin Board |
|
| Help |
|
| CCTV News |
|
| Return Policy |
|
|
QAM. Quadrature amplitude modulation. Method for modulating
two carriers. The carriers can be analog or digital. Quad compressor (also split screen unit). Equipment that simultaneously displays parts or more than one image on a single monitor. It usually refers to four quadrants display. Radio frequency (RF). A term used to describe incoming radio signals to a receiver or outgoing signals from a radio transmitter (above 150 Hz). Even though they are not properly radio signals, TV signals are included in this category. RAM. Random access memory. Electronic chips, usually known as memory, holding digital information while there is power applied to it. Its capacity is measured in kilobytes. This is the computer’s work area. RAID. Redundant arrays of independent disks. This a technology of connecting a number of hard drives into one mass storage device, which can be used, among other things, for digital recording of video images. Random interlace. In a camera that has a free-running horizontal sync as opposed to a 2:1 interlace type that has the sync locked and therefore has both fields in a frame interlocked together accurately. Registration. An adjustment associated with color sets and projection TV’s to ensure that the electron beams of the three primary colors of the phosphor screen are hitting the proper color dots/stripes. Resolution. A measure of the ability of a camera or television system to reproduce detail. The number of picture elements that can be reproduced with good definition. Retrace. The return of the electron beam in a CRT to the starting point after scanning. During retrace, the beam is typically turned off. All of the sync information is placed in this invisible portion of the video signal. May refer to retrace after each horizontal line or after each vertical scan (field). Remote control. A transmitting and receiving of signals for controlling remote devices such as pan and tilt units, lens functions, wash and wipe control and similar. RETMA. Former name of the EIA association. Some older video test charts carry the name RETMA Chart. RF signal. Radio frequency signal that belongs to the region up to 300 GHz. RG-11. A video coaxial cable with 75-W impedance and much thicker diameter than the popular RG-59 (of approximately 12 mm). With RG-11 much longer distances can be achieved (at least twice the RG-59), but it is more expensive and harder to work with. RG-58. A coaxial cable designed with 50-W impedance; therefore, not suitable for CCTV. Very similar to RG-59, only slightly thinner. RG-59. A type of coaxial cable that is most common in use in small to medium-size CCTV systems. It is designed with an impedance of 75-W. It has an outer diameter of around 6 mm and it is a good compromise between maximum distances achievable (up to 300 m for monochrome signal and 250 m for color) and good transmission. Rise time. The time taken for a signal to make a transition from one state to another; usually measured between the 10% and 90% completion points of the transition. Shorter or faster rise times require more bandwidth in a transmission channel. RMS. Root Mean Square. A measure of effective (as opposed to peak) voltage of an AC waveform. For a sine wave it is 0.707 times the peak voltage. For any periodic waveform, it is the square root of the average of the squares of the values through one cycle. ROM. Read only memory. An electronic chip, containing digital information that does not disappear when power is turned off. Routing Switcher. An electronic device that routes a user-supplied signal (audio, video, etc.) from any input to any user-selected output. This is a broadcast term for matrix switchers, as we know them in CCTV. RS-125. A SMPTE parallel component digital video standard. RS-170. A document prepared by the Electronics Industries Association describing recommended practices for NTSC color television signals in the United States. RS-485. This is an advanced format of digital communications compared to RS-422. The major improvement is in the number of receivers that can be driven with this format, and this is up to 32. RS-232. A format of digital communication where only two wires are required. It is also known as a serial data communication. The RS-232 standard defines a scheme for asynchronous communications, but it does not define how the data should be represented by the bits, i.e., it does not define the overall message format and protocol. It is very often used in CCTV communications between keyboards and matrix switchers or between matrix switchers and PTZ site drivers. The advantage of RS-232 over others is its simplicity and use of only two wires. RS-422. This is an advanced format of digital communication when compared to RS-232. The basic difference is in the need for four wires instead of two as the communications is not single-ended as with RS-232, but differential. In simple terms, the signal transmitted is read at the receiving end as the difference between the two wires without common earth. So if there is noise induced along the line, it will be cancelled out. The RS-422 can drive lines of over a kilometer in length and distribute data to up to 10 receivers. Saturation (in color). The intensity of the colors in the active picture. The degree by which the eye perceives a color as departing from a gray or white scale of the same brightness. A 100% saturated color does not contain any white; adding white reduces saturation. In NTSC and PAL video signals, the color saturation at any particular instant in the picture is conveyed by the corresponding instantaneous amplitude of the active video sub-carrier. Scanning. The rapid movement of the electron beam in the CRT of a monitor or television receiver. It is formatted line-for-line across the photo-sensitive surface to produce or reproduce the video picture. When referred to a PTZ camera, it is the panning or the horizontal camera motion. Scanner. 1. When referring to a CCTV device it is the pan only head. 2. When referring to an imaging device it is the device with CCD chip that scans documents and images. Scene illumination. The average light level incident upon a protected area. Normally measured for the visible spectrum with a light meter having a spectral response corresponding closely to that of the human eye and is quoted in lux. Scotopic vision. Illumination levels below 10–2 lux, thus invisible to the human eye. SCSI. Small computer systems interface. A computer standard that defines the software and hardware methods of connecting more external devices to a computer bus. SECAM. Sequential Couleur Avec Memoire, sequential color with memory. A color television system with 625 lines per frame (used to be 819) and 50 fields per second developed by France and the former U.S.S.R. Color difference information is transmitted sequentially on alternate lines as an FM signal. Serial data. Time-sequential transmission of data along a single wire. In CCTV, the most common method of communicating between keyboards and the matrix switcher and also controlling PTZ cameras. Serial interface. A digital communications interface in which data are transmitted and received sequentially along a single wire or pair of wires. Common serial interface standards are RS-232 and RS-422. Serial port. A computer I/O (input/output) port through which the computer communicates with the external world. The standard serial port is RS-232 based and allows bidirectional communication on a relatively simple wire connection as data flow serially. Sidebands. The frequency bands on both sides of a carrier within which the energy produced by the process of modulation is carried. Signal-to-Noise ratio (S/N). An S/N ratio can be given for the luminance signal, chrominance signal and audio signal. The S/N ratio is the ratio of noise to actual total signal, and it shows how much higher the signal level is than the level of noise. It is expressed in decibels (dB), and the bigger the value is, the crisper and clearer the picture and sound will be during playback. An S/N ratio is calculated with the logarithm of the normal signal and the noise RMS value. Silicon. The material of which modern semiconductor devices are made. Simplex. In general, it refers to a communications system that can transmit information in one direction only. In CCTV, simplex is used to describe a method of multiplexer operation where only one function can be performed at a time, e.g., either recording or playback individually. Single-mode fiber. An optical glass fiber that consists of a core of very small diameter. A typical single-mode fiber used in CCTV has a 9 mm core and a 125 mm outer diameter. Single-mode fiber has less attenuation and therefore transmits signals at longer distances (up to 70 km). Such fibers are normally used only with laser sources because of their very small acceptance cone. Skin effect. The tendency of alternating current to travel only on the surface of a conductor as its frequency increases. Slow scan. The transmission of a series of frozen images by means of analog or digital signals over limited bandwidth media, usually telephone. Smear. An unwanted side effect of vertical charge transfer in a CCD chip. It shows vertical bright stripes in places of the image where there are very bright areas. In better cameras smear is minimized to almost undetectable levels. SMPTE. Society of Motion Picture and Television Engineers. SMPTE time code. In video editing, time code that conforms to SMPTE standards. It consists of an 8-digit number specifying hours: minutes: seconds: frames. Each number identifies one frame on a videotape. SMPTE time code may be of either the drop-frame or non-drop-frame type. Snow. Random noise on the display screen, often resulting from dirty heads or weak broadcast video reception. S/N ratio. See Signal-to-noise ratio. Spectrum. In electromagnetics, spectrum refers to the description of a signal’s amplitude versus its frequency components. In optics, spectrum refers to the light frequencies composing the white light which can be seen as rainbow colors. Spectrum analyzer. An electronic device that can show the spectrum of an electric signal. SPG. Sync pulse generator. A source of synchronization pulses. Split-screen unit (quad compressor). Equipment that simultaneously displays parts or more than one image on a single monitor. It usually refers to four quadrants’ display. Staircase (in television). Same as color bars. A pattern generated by the TV generator, consisting of equal width luminance steps of 0, +20, +40, +60, +80, and +100 IRE units and a constant amplitude chroma signal at color burst phase. Chroma amplitude is selectable at 20 IRE units (low stairs) or 40 IRE units (high stairs). The staircase pattern is useful for checking linearity of luminance and chroma gain, differential gain and differential phase. Start bit. A bit preceding the group of bits representing a character used to signal the arrival of the character in asynchronous transmission. Sub-carrier (SC). Also known as SC: 3.58 MHz for NTSC, 4.43 MHz for PAL. These are the basic signals in all NTSC and PAL sync signals. It is a continuous sine wave, usually generated and distributed at 2V in amplitude, and having a frequency of 3.579545 MHz (NTSC) and 4.43361875 MHz (PAL). Sub-carrier is usually divided down from a primary crystal running at 14.318180 MHz, for example, in NTSC, and that divided by 4 is 3.579545. Similar with PAL. All other synchronizing signals are directly divided down from sub-carrier. S-VHS. Super VHS format in video recording. A newer standard proposed by JVC, preserving the downwards compatibility with the VHS format. It offers much better horizontal resolution up to 400 TV lines. This is mainly due to the color separation techniques, high-quality video heads and better tapes. S-VHS is usually associated with Y/C separated signals. Sync. Short for synchronization pulse. Sync generator (sync pulse generator, SPG). Device that generates synchronizing pulses needed by video source equipment to provide proper equipment video signal timing. Pulses typically produced by a sync generator could be sub-carrier, burst flag, sync, blanking, H and V drives and color black. Most commonly used in CCTV are H and V drives. |