4K: How to Meet the Single Link Challenge?

One of the greatest challenges presented by the arrival of 4K video is in the ability of this signal to be carried by a single copper coaxial cable, commonly called “single link”.

Proposed Change in Distance Calculations

It is most important for a broadcaster to know how far he can transmit a signal over a single coax cable. In recent years Belden has proven that the recommended SMPTE distance calculation for HD signals can be outperformed. The original distance formula, -20 dB at ½ clock, was a reasonable “safe” value for 1990 and the technology then available. However, we believe that more than 20 years of improvements in chip design and active equipment has enabled us to surpass this calculation. Therefore, we think that a new formula, -40 dB at ½ clock, is an appropriate “safe” distance. And in the ‘real world’, Belden can go considerably further than that.


Let’s have a look at the green squares in the chart: Belden’s 1694A for example can run a minimum 113 meter with HD. With 2K signals 1694A runs a minimum of 78 meters, or 35 meters less when compared to HD. In general, all these lengths can be improved on by using our HD coaxial cables and BNC connectors. See for example the 140 meter at HD with 1694A.

If you remember that the bandwidth of 4K is 8 times HD and 4 times 2K, everyone would expect the minimum distance of a 4K signal to be less than HD or 2K. But look at the red squares. The chart clearly shows how Belden’s 1694A runs 106 meter with QuadFull-HD on a single-link! In other words: 28 meters further than 2K.

Now have a look at the column for Dual-link – which covers two coaxial cables using the same bandwidth of 2K on each cable. Both cables can share the total bandwidth and therefore it will be possible to double the lengths of 2K to 156 meter. How is that possible?  Well, recent technology is able to tolerate higher attenuation! With this in mind, a proposed change in distance calculations was submitted to the SMPTE work groups.

Belden believes that our current cable line will work to 6G; whereas 12G will require re-design and new cables. That is the reason why the single-link values at ‘true” 4K are colored light-blue. This means that those values show new 4K designed cables which currently do not exist.

So coax will still be alive in the 4K future

Stay tuned! In my next blog post will talk about “true” 4K cable and connector designs.

If you need more details about our solutions let me know and Email me at werner.eich@belden.com


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