12G-SDI Distance Challenges to Consider for Media & AV Projects
Bandwidth demand is scaling rapidly as the world of broadcast, AV, media, and entertainment welcomes trends like cloud computing, big data and artificial intelligence, along with high-definition video formats like 4K and 8K.
While applications involving 3G-SDI and 6G-SDI bandwidths are still prevalent today, a new SDI standard for broadcast has entered the scene. 12G-SDI supports a data rate of roughly 12 Gb/s; it enables technology like 4K and 8K video transmission.
In terms of planning, equipment and deployment, 3G-SDI and 6G-SDI applications have been pretty straightforward. Projects that require 12G-SDI support, however—such as those incorporating professional cameras and displays, production/post systems and format converters, routers and servers—may create distance challenges that need to be considered before you invest in design and equipment.
Cable lengths for 12G-SDI applications
Some designers use fiber optic cabling to achieve longer distances in 12G-SDI applications, but there are quite a few applications where coax is still the best fit. Coax cables designed for SDI signals are offered in multiple variations—riser, plenum, LSZH, high-flex, gel-block outdoor versions, etc.—as well as in many sizes, ranging from miniature RG-59 to RG-11.
With all these choices, however, designers need a way to determine how far they can run each cable type. To help, we created an Estimated Transmission Distance Chart at Serial Data Rates based on the cable loss values for given formats as specified by SMPTE. The chart establishes estimated distances that Belden cables can support in broadcast and AV applications.
However, actual cable distances can be shorter or longer based on the equipment being used. As new formats and new versions of cables become available, the chart is updated.
How to use the Estimated Transmission Distance Chart
Based on attenuation or signal loss at one-half the signal frequency as defined by SMPTE and signal type, the Estimated Transmission Distance Chart we created defines values for cables only; it doesn’t include connectors, bulkheads or other items used to connect cables that add loss.
While this table is helpful, it’s not the be-all and end-all. It comes with this important caveat: As the calculated distances are approached, the bit error rate (BER) can vary dramatically. BER depends on the receiver’s design and the losses of the coax used.
Although cable performance is associated with a distance as listed in the distance chart, active equipment may perform above or below the standards loss.
12G-SDI applications follow the SMPTE ST 2082-1:2015 (12 Gb/s Signal/Data Serial Interface – Electrical) standard. It establishes requirements for high-speed (12G) digital video using SDI standards and describes the suitable electrical and physical characteristics of a 12G-SDI coaxial cable. Typical loss amounts for receivers (such as cameras, central control units, etc.) that operate within a 12G-SDI channel are also defined in the standard: up to -40 dB at one-half the clock frequency (6 GHz). In other words, to prevent performance problems, attenuation loss along the channel from the transmitter to the receiver should be no higher than -40 dB.
But the SMPTE ST 2082-1 standard also allows variance from this -40 dB threshold. It states: “… however, receivers designed to work with greater or lesser signal attenuation are acceptable.” While -40 dB is typical for receivers, equipment that operates with higher or lower amounts of loss is also acceptable, according to the SMPTE standard.
This deviation from the -40 dB recommendation wasn’t a major concern for previous technologies, like 3G-SDI, which had a level of -20 dB, because the equipment wasn’t close to falling off the digital cliff—the equipment operated well above the threshold, which prevented sudden failures. In 12G-SDI applications, however, that isn’t the case.
When transmitting at 12G, you quickly approach the noise floor of the equipment (the amount of noise it generates without a signal) and reach that digital cliff. Because there are no interoperability test standards to verify that broadcast equipment will—or should—operate within certain attenuation parameters, it’s important to know what you’re up against when working with 12G-SDI applications.
If a cable is deployed in accordance with the Estimated Transmission Distance Chart but receives no signal (or experiences lots of attenuation), then it’s likely that the cable did not create the performance issue (as long as the cable is installed correctly and not damaged). Instead, the chosen equipment doesn’t support the -40 dB threshold.
The Road to 12G-SDI: How Far Can Your Cable Run?
To explain the impacts of this situation, and how to navigate it as you design and invest in equipment, we developed a helpful whitepaper to serve as your guide.
This whitepaper will help you determine whether your equipment supports recommended cable distances as identified in the Estimated Transmission Distance Chart. It also takes a close look at what our attenuation testing reveals about cable distance in 12G-SDI applications.
To see the full story, download the whitepaper below. If you need help determining appropriate cable distances for your 12G-SDI application to avoid falling off the digital cliff, remember: Belden is here to help.