Using the right SDI for the right purpose

Cable choices are numerous. Options abound when you’re looking at analogue versus digital; HD versus SD; and on and on. As we finish our series on Choosing the Right Video Cable, feel free to take a look back at the discussions on VGA, DVI, and HDMI in comparison to SDI.

SDI is a professional digital video standard developed for broadcast video. SDI carries uncompressed digital video and 16 channels of PCM audio. SDI is transmitted over 75 Ohm coax cable with BNC connectors, typically RG-6.

There are 4 common SDI standards. The original SDI supports 480i video, HD-SDI increased the supported resolution to 1080i/720p. 3G-SDI supports 1080p, and 6G-SDI supports up to 4K at 30Hz. The12G-SDI is still in draft status, but it will support 4K signals at 60Hz.

HD-SDI and above can be run up to 300’. After 300’ it can be reclocked and sent an additional 300’. If you need to carry the high-resolution uncompressed signal over long distances SDI is the way to go.

The downside to SDI is that, as a professional standard, many consumer and prosumer video devices do not natively support it. Several companies are making converter boxes that convert to and from SDI signals. SDI is also very limited in which resolutions it supports, especially SD resolutions.

When buying coax cable for an SDI system pay attention to what you are buying, not all BNC cables are created equal. SDI can use RG-59 and RG-6 cable, although RG-6 cable is necessary for long runs and preferred in general. RG-59 cable, while cheaper, is less suitable for runs much over 100’. Also, be aware that RG-59 comes in 50 Ohm and 75 Ohm versions. 75 Ohm cable is needed for SDI.

This SDI Cable Guide gives more details to help you decide what is best for your next event.

Let us know if you have any questions or need further assistance making the choice on which cable to go with for your next production, event, sporting event, or installation.

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