|Sunday, 22 October 2006|
A video cable is required to transmit signals in such states that the transmission signals are prevented from being attenuated and major frequency components of the signals to be transmitted are faithfully maintained, in order to increase the transmission efficiency of signals transmitted by the cable. Video may be transmitted either in digital or analog formats. For digital video transmission such as computer video, cable insertion loss is generally not an issue because the digital signal can be recovered so long as discernable digital pulses are received at the receiving station. For analog signals, the signal is just voltages, and voltages are affected by wire length, connectors, heat, cold, and other conditions. This degrading effect on the video signal caused by the transmission cable length is known as cable insertion loss. In the processing of video signals, it is often found that the video signal is attenuated by the cable to such an extent that a correction is required to compensate the signal for the cable attenuation. Therefore, video cables are variously designed to decrease the attenuation and strain of a signal waveform and to eliminate influences due to external noise by improving the amplitude characteristics and phase characteristics of signals to be transmitted. Whether used for audio or general data transfer purposes, signal degradation is usually caused by cable impedance. High impedance cables can reduce received signal strength, and thereby degrade overall system performance. Recognizing that cables can have a noticeable effect on signal output quality, a variety of techniques have been used to eliminate signal degradation caused by the signal cable when they are connecting system components. The use of shields protects the signal leads from external signals which are not generated by the system components. Thus, shields have improved overall system performance by protecting signal transfers from being degraded by noise or signals from the external environment.
A coaxial cable is typically used for transmission of high resolution video because of its superior performance over twisted pair cable. Coaxial cables are used in many areas such as transmission and computer cables, computer networking, video signal transmission, instrumentation cables, broadcast cables, and lightweight coaxial cables for satellites. Conventionally, a two-strand coaxial cable equipped with a pair of signal lines and shielded by a shielding line via an insulating layer and a set of coaxial cable which shields a signal line with a shielding line via an insulating layer have been used as a video cable making a connection between video devices. Coaxial cables are usually composed of an elongated outer tubular conductor of metal containing a concentrically situated elongated central conductor of metal, both conductors being separated by a layer of an electrically insulating material. The central conductor may be composed of a single wire or bundle or wound wires. The USB technology may greatly simplify the complex cabling that typically spills out from the back of personal computers. USB peripherals may include keyboard, mouse, digital camera, phone/answering machine, printer, scanner, fax/modem, game controller, light pen, digital audio, and any other USB compliant device. The short latencies for packet transmission allow the USB to be transaction oriented with very little performance loss. The USB cable is a four wire cable, and the maximum cable length is about five meters. The maximum USB cable length of about five meters results from the fact that the USB controller considers any transmission return time greater than a characteristic threshold value to be an error.