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The professional video and broadcasting business is in the midst of a radical change. Demand for bandwidth has soared with the universal use of 4K, Ultra-HD, and a new technology 8K. The 12G-SDI, the most recent video standard, demands data rates of up to 12 Gbps, which pushes the coaxial cable assemblies to the edge of their performance. In comparison with typical RF usage, video requires a high degree of signal integrity and small form factors, as well as precise 75-Ohm impedance matching. Linkworld, having more than 20 years of experience in RF, is aware of the specific requirements of high speed video applications. This guide discusses important aspects to be taken into consideration when using coaxial cable assembly in current video transmission.
The 75-Ohm Standard and Impedance Precision
Video Systems work at a completely different standard of impedance to RF counterparts. Whereas 50-Ohm systems are usually used in telecommunications, broadcast systems need to be 75-Ohm characteristic impedance. This difference is essential--when a 50-Ohm connector is inserted into a 75-Ohm video circuit, the instant impedance mismatch occurs, producing signal reflections in the form of artifacts in the picture, jitter or loss of signal altogether. The current standard of 12G-SDI requires close regulation of the signal path impedance. Video coaxial assemblies typically have high-quality tolerances of impedance, which is achieved by the use of tightly controlled dielectric materials and a close manufacturing process. Linkworld assemblies are video-grade, designed to be used in 75-Ohm applications, which allows it to maintain the impedance at all interfaces.
Supporting 12G-SDI and Beyond
Development of SDI standards has spurred design improvements in cable assembly. 12G-SDI, which is the standard of 4K video at 60 fps at a single coaxial cable, needs cable assembly that can support a frequency up to 12 GHz. This introduces challenges previously associated with microwave applications, such as critical insertion loss and return loss, which can degrade picture quality. Video assemblies today make use of finely-crafted cable designs with dielectrics carefully engineered and braided shields of high coverage to minimize loss without compromising flexibility. There are 75-Ohm MCX, HD-BNC and micro-coaxial connector families that are optimized for 12G-SDI. The video assemblies at Linkworld are engineered and tested to support or surpass 12G-SDI.
Miniaturization Trends in Broadcast Equipment
As video equipment becomes more compact while channel density increases, connector physical size has become a critical consideration. Broadcast cameras and routing switchers put unprecedented functionality into a small rack space. This is impelling the use of miniature connector families which are video friendly. Only 75-Ohm versions are possible and in a much smaller size than standard BNC connectors, the MCX series features high performance up to 12 GHz. To make the application even smaller, micro-coaxial connectors such as Hirose D.FL75 series can be used with 12G-SDI and do not consume any more than 4mm x 4mm of board space, which makes them perfect when used to wire up cameras internally. Linkworld provides a wide variety of miniature video interfaces and high-density custom assemblies to enable equipment manufacturers to achieve maximum channel density without affecting signal quality.
Cable Construction and Transmission Distance
Professional video installations are commonly characterized by transmission distance defining system architecture. Various cable types provide size, flexibility and reach trade-offs. Normal flexible video cables (RG6 or RG59) perform reasonably well over medium ranges, to about 105 meters when using RG6 with 12G-SDI signals. More expensive precision broadcast cables with larger center conductors and more advanced dielectrics are used to further extend the range of longer runs; high-quality RG11 cables can carry 12G-SDI over a range of 227 meters. In cases where permanent installations need absolute performance, low-loss trunk cables minimize attenuation across hundreds of meters. The advantage of equipment room jumpers is the very adaptable cables which are not subject to continuous flexing. The custom capabilities in the case of Linkworld are between this range and thus gives the opportunity to have the best cable construction on the basis of every segment of the infrastructure.
The direct requirements of coaxial assemblies to a high-speed video transmission include: 75-Ohm impedance, 12G-SDI transmission of video, miniaturization trends, and transmission distance. With the development of video formats to more advanced resolutions, the quality of interconnect deteriorates and becomes more important. Linkworld has more than 20 years of experience in manufacturing RF and extensive knowledge of video transmission, which offers custom assemblies, adapters, and connectors that can be utilized to deliver the transfer of video in broadcast and professional AV without errors. Call us to talk about your high speed video interconnect needs.