A Look at New Coaxial Cable Design for “True” 4K

Multi-cable formats (dual and quad links) can be used today because the bandwidth on each cable is the same as HD or 3G bandwidths currently used.  This is possible because recent video cards contain chips that will separate the video data misc. sign 9_Original_22638into two or four signals. The signals then run over separate coax cables at a maximum speed of 3GHz (3GHz for 3G and 1.5 GHz for HD) and at the receiver, they will be transformed back to 6GHz or 12 GHz. Belden believes that its current line of cables will work to 6 GHz, but 12 GHz will require re-design and new cables.

New Cable Design

There are a number of things that can be done to improve performance of the 4K versions listed above. First is to increase Velocity of Propagation (Vp) by means of nitrogen gas injection. The limits of this technique are closely guarded secrets for most manufacturers. So can we get much higher? The problem is, as more nitrogen gas is added, dimensional stability suffers. This leads to impedance variations or “return loss”, which negatively affects performance. The solution is to reduce the size of the bubbles in the foam. Belden already offers better Vp in its well-known RF cable line with a Velocity of Propagation of 86% – 1694A has currently 82%. Unfortunately these RF cables are 50 ohm and not 75 ohm as needed in the broadcast world. So, there is still some work to be done. Thankfully Belden has both the technology and the experience, so we will be able to develop the correct cable for this new 12 GHz requirement. Improvements in shield design, such as multi-layer shielding, are also possible, although these improvements are not tied to the raw performance, such as attenuation. But shielding is certainly tied to noise immunity, which speaks to signal integrity in longer runs or noisy environments.

What About Connectors?

We see a trend towards DIN 1.0/2.3 connectors instead of BNC connectors at those high frequencies needed for “true” 4K. The outer diameter of a DIN 1.0/2.3 connector is much smaller compared to traditional BNC types. The smaller DIN 1.0/2.3 connectors (secure locking with push/pull) are less stressed than traditional BNCs, and they do not require a tight bending radius. This contributes to a better RF launch profile, and a better return loss. The smaller dimension of a DIN connector is an advantage: because of their specific design, DIN connectors for such high frequencies (up to 12 GHz) are easier to manufacture than traditional BNC connectors. Which design will ultimately take the lead? The future will tell.

Conclusion

If the revised distance formula, -40 dB at ½ the clock, is adopted, and if performance improvements are made, such as higher Velocity of Propagation, single-link coaxial cable for 4K formats will be able to provide the right performance for future video transmission.

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

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