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Putting Optical Wavelength Management To Work

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Managing cables and long-distance signal transport, especially in outside broadcast situations, has long been an expensive, bulky, time-consuming nuisance.

Look at any truck compound at any venue, and you'll see the amount of cable and rigging time that goes into ensuring signals get where they need to go, and the job gets trickier with each additional camera. Add to that the potential for interference, noise and crosstalk, and it's easy to understand why those production scenarios are so challenging.

Now that more productions are being shot in 4K, the problem has grown exponentially. Typically, output from 4K cameras comes in the form of four 3G signals transported via four coaxial cables coming from the side of the camera. That means four cables per camera are going back to the truck from the camera location, whereas in years past there would only have been one. Imagine being in a stadium doing a full 4K shoot with 16 cameras. That's a lot of copper cable to route through the nooks and crannies of a stadium and back to the truck – representing a lot of rigging time, cable expense, and potential for failure.

Fortunately, fiber can make the job much easier. Using fiber instead of coax means you can transport all four 3G signals on one cable. There are a couple ways to do it: coarse wave division multiplexing (CWDM), which converts the 3G signals onto different wavelengths of light and combines them onto one fiber, and time division multiplexing (TDM), which effectively serializes the four 3G signals onto a 12G single-wavelength fiber channel.

The method you choose depends on available resources. CWDM is an affordable and efficient way of doing it, but it ties up four wavelengths. So, if you're doing a multicamera shoot and have a limited number of fibers to work with, it makes more sense to use TDM. Once the 12G signal is multiplexed via TDM, then you can use CWDM to multiplex signals from several cameras onto one fiber as needed.

Either way, using fiber-optic cable rather than copper cuts rigging time and cable bulk significantly. Furthermore, fiber is more resilient and offers better noise isolation, and the signals can travel much farther on fiber (30-40 kilometers) than on copper (70-100 meters). As long as you keep the contacts and terminations clean, fiber transport will work perfectly and very efficiently, even at the higher bit rates associated with 12G signals.

Using fiber for 12G video transport has become a reality because of products such as Bluebell's new suite of 12G-SDI cards and stand-alone interfaces. CWDM is made possible through both the BC366 and BC370 optical converters, which attach to the side of a 4K camera and have four BNC inputs and one optical output or four optical outputs, respectively. Meanwhile, the BC390 interface handles TDM by receiving four 3G-SDI inputs and serializing them to one 12G-SDI output on both BNC and fiber ports simultaneously, or vice versa.

Now, with wavelength management, Bluebell products can carry 16 wavelengths on a single fiber. Even better, they can also handle 16 4K camera outputs on a single fiber. Couple that with the standard SMPTE hybrid cable, which has two fiber cores, and you can immediately move 32 4K UHD channels over a single SMPTE hybrid cable – something every truck in the industry carries by kilometers.

When you put wavelength management to work in your 4K production workflow, you can eliminate piles of bulky copper cable, reduce set-and-strike time, and ensure reliable 12G signal transport over long distances.

This article is also available to read in the June edition of Broadcast Film & Video.

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