Fiberize your broadcast facility
Mar 1, 2007 12:00 PM, STEVE LAMPEN, BOB SEBESTO AND KIP COATES
While copper-based cables have been successfully used up to 1000ft to carry HD signals, fiber cables carry longer distances. Typical broadcast applications for fiber-optic cabling include large sports venues used for the Olympic Games, NASCAR races, PGA golf tournaments and Major League Baseball stadiums, such as the St. Louis Cardinals’ new Busch Stadium shown here.
In reality, there is no such word as fiberize. But since the introduction of fiber-optic cables in the 1970s, every year has been proclaimed the year that broadcasters would go fiber. When the move to HD started in the 1990s, the industry once again heard the fiber's siren song. But few went that route. Virtually all signal-carrying media in the broadcast arena is still copper-based cables. So what happened?
Broadcast engineers are a savvy lot. They do not jump on a new technology simply because it's there, as consumers often do. Before adopting a new way of doing things, broadcast engineers want to know that the change will:
simplify their broadcast lives;
reduce the cost of what they are doing;
allow them to do something they could not do otherwise; and
improve the performance of their systems.
When HD appeared on the scene, manufacturers developed copper cables that offered improved designs, improved materials and, most important, performance far beyond what was possible with existing classic copper cables. Today, there are copper digital video cables tested to 4.5GHz bandwidth, with guaranteed return loss numbers, designed specifically for use in SuperHD and other high-bandwidth applications. Some cables, such as RG-11, have been successfully used up to 1000ft carrying HD signals — even though their recommended distance is 550ft.
A thousand feet covers a lot of ground. This leaves a few long-run applications as fiber territory. Some examples include voice, data and video for new stadiums and large sports venues for the Olympic Games, golf events and NASCAR, as well as building-to-building tie lines, building and studio backbones, and the ability to interface with the phone company or other carriers.
One growing trend in the broadcast industry is the use of tactical fi ber-optic cables to replace standard SMPTE or triax cables for remote fi eld applications. These cables are not only lighter in weight than traditional cabling, but also smaller in size.
Fiber also has the lock on bandwidth. Although 4.5GHz might be cutting edge for coax, it's child's play for single-mode fiber. In fact, the only limitation on single-mode cabling is how much you are willing to spend on the boxes. (There are even commercial drivers up to 100GHz.) For those wanting to stay with lower-cost components, high-bandwidth (2GHz to 4GHz) 50µm multimode fiber is also an option for links up to 550m (1804ft).
Meanwhile, we have the advent of 10GigE networking on copper cables, specifically 10GBASE-T using Cat 6a. But, like all category cables, this is limited to 100m (328ft), and many proposed cables cannot even go that far. With 10GB, you could run six HD bit streams — if you could get them into an Ethernet format. We might be approaching or even equaling the bandwidth of many fiber systems with these kinds of copper cables, but fiber still cannot be beat on distance.
Many studios have added fiber to their backbones, while still relying on category cables for horizontal cabling. While multimode fiber is still the norm for traditional networking applications, single-mode fiber is the choice for the majority of broadcast applications.
Price point
The cost of fiber can't be beat. Fiber is inexpensive. The cost of the fiber has never been the stumbling block. It is the cost of conversion that has been the problem.
Copper cables can simply attach from output to input, with no conversion or other boxes required. This makes copper cheaper, easier to install, and arguably, more reliable (at least with fewer points of failure).
Sound choice
One of fiber's benefits is noise immunity. Because fiber cables run optical signals, they are completely immune from RFI, EMI or any other electromagnetic source of interference. This means you could install fiber-optic cable on your broadcast antenna, and it would work fine. I'm not sure why anyone would want to do that, but if you had an application for it, you could.
The only problem is that the source and destination boxes do not use optical signals inside and lack any immunity to electromagnetic interference. So, until we have devices that manipulate (i.e. amplify) the signal optically, we will be stuck with electronic boxes and optical conversion in and out. Where's my optical transistor? Along the same lines, a fiber cable, if it is fiber only (i.e. does not contain any metal), can be lightning-proof as well.
Many HD mobile production studios, such as the Dome Productions truck shown here, carry reels of tactical fi ber to roll out to remote sites, whether across a golf course, on a professional football field, or through the streets of Times Square for a special event in New York City.
Fiber moves in
Broadcast antennas aside, there are some places and reasons for fiber's use, and it is slowly and inexorably moving into the broadcast realm. Perhaps one reason is because all these signals are now digital video and audio. In other words, they are data. Fiber and data have had a long and fruitful marriage, so there is a lot of engineering expertise — and fiber products — to play with your data (video or otherwise).
Digital signals are different from traditional analog signals. They can be shipped, manipulated, stored, transmitted, reassembled and used as a data bit stream — and then turned back into video whenever convenient. And that convenient point might just be the consumer plasma screen on the living room wall.
The SMPTE 311M standard
SMPTE has a standard for fiber-optic camera cable called SMPTE 311M. This cable contains both fiber and copper elements and is the standard for HD cameras. These cables, however, can be problematic, especially when used in a remote truck or van.
Here's why: When a single-mode fiber breaks, you can't simply get out a razor blade and a couple of tools and fix it the way you could repair triax in the analog world. Therefore, you will have to carry extra fiber-optic camera cables in your truck in case one of them fails. And any truck weight savings you may have realized because of these low-weight cables is now gone.
The trouble with triax
When broadcasters looked at triax to carry digital signals, they found that it works fine for SDI (270Mb/s at 135MHz) but was difficult for HD (1.485Gb/s at 750MHz). And when some users said they wanted to go a minimum of 1000m (3280ft), there was no way any triax could do that with HD. So that was the end of triax.
You might disagree, saying there are many cameras running HD down triax. However, if you read the fine print, you will learn that it is not true digital HD down triax. It is converted to wideband analog video and is then converted back to digital HD at the receiving end. Because the transmission over the triax is analog, it is more susceptible to EMI (noise), which, when converted back to digital, can potentially produce artifacts in the video image.
Some advantages of tactical fiber cabling for fifield applications are that it can be rolled off the reel and deployed effectively on-site over extended distances from 1km (0.6mi) to 2km (1.2mi). And because the cables are built to military standards, they can stand up to repeated redeployment and outdoor environments.
The tactical response
One increasingly popular option is the use of tactical fiber-optic cables, which replace standard SMPTE or triax cables for remote applications. These cables are not only lighter than traditional cabling but are also smaller and can be used for extended distances, such as 1km (0.6mi) to 2km (1.2mi).
Because tactical fiber-optic cables are based on military standards, they can easily withstand constant redeployments, as well as the abuse often associated with cables strung out over a golf course for a week or in the streets of New York City. Additionally, with some of the new field installable connectors, such as Optimax, broadcasters can repair broken fibers in minutes rather than hours.
At the beginning of this article, we discussed how we could take HD signals up to 1000ft of RG-11. If we ran HD signals down fancy new RG-11 triax of the same construction, 1000ft would cover a lot of ground. It would certainly cover all the studio installs and might even cover many small and midsized sports venues. And, if this cable broke, you could repair it on the spot. All we have to do then is convince the camera manufacturers that HD on triax would work for a multitude of installations and ask them to offer that as an option on their HD cameras.
Steve Lampen is multimedia technology manager, Bob Sebesto is fiber optics business development manager, and Kip Coates is entertainment products marketing manager for Belden.
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