The fact of being able to repair a fiber in the field in less than a minute makes him win many friends, especially in the emergencies of the audiovisual field.
Juan Manuel Cortés*
Usually, when we talk about fiber in television, we traditionally refer to "SMPTE" cable (specifically, the SMPTE 311 standard for cable and 304 for connector), a type of solution composed of fiber (two OS2 wires) and several copper pairs for intercom, TC, etc., used in the connection of professional cameras.
However, once the SMPTE 2110 standard for uncompressed broadcast signal over the IP protocol was recently approved, terms such as "broadcast datacenter" are beginning to appear, where IT and AV promise each other eternal love. And, as is often the case in any marriage, the parties must accommodate their respective interests with as few arguments as possible.
How is the bandwidth of a video over IP signal calculated? Multiply the resolution (horizontal x vertical) by the number of fields per second. We multiply the result again by the color depth (are we sampling at 8 bits, 10 bits, 12 bits?), and finally by 3 (RGB). As soon as we make a conservative calculation, we will realize that it is dangerously close to 10 Gigabytes per second (just the parameter of the CAT6a cable).
Therefore, with the trend to 4K, it is fiber that is taking over from copper in television signal production environments. As you know, the optical fiber can handle the 40 Gigabytes of information per second without disheveling, something only accessible to the future CAT8 (which is copper).
What fiber to use? The choice usually does not depend on the installer but on the manufacturer of the active equipment (cameras, routers, media converters, etc.), which dictates the type of fiber (multimode or single-mode) as well as the type of connector (LC, SC, ST ...). What we should know is that multimode fiber is suitable for short distances (100, 150 and 200 meters at the speed mentioned above), and that the most used today is the OM3, with the OM4 taking over, and the new OM5 for future expansions.
There is another type of optical fiber, more suitable for long distances, the single-mode (OS2) through which a beam of light circulates that modulates the information in a specific wavelength to this fiber (1310 and 1550 nm).
How easily does fiber optics break? The current ones of a certain quality endure a lot of abuse before breaking. But we must not forget that they have a radius of curvature that we must respect. If we do not, the loss that the manufacturer manifests in the catalog can skyrocket and, therefore, the transducer equipment at destination may not have enough light to "see" any signal.
What about field connectorization? Formerly it was a laborious job (sandpaper and more sandpaper ...). However, today there are new methods of connectorization much simpler and more agile. The most disruptive case was mechanical insertion. Suddenly, it was no longer necessary to fuse the fiber to put a connector on it.
Effectively this method supposes a certain loss (0.2, 0.3dB... depending on the skill of the installer) which, however, is a sufficient margin that many applications support perfectly. If our loss budget is 2.3 dB (example), we are covered. And the fact of being able to repair a fiber in the field in less than a minute makes him win many friends, especially in the emergencies of the audiovisual field.
To the traditional technique of splicing fiber (specifically we fuse the fiber with a "pigtail", which is a patch cord connectorized in the factory on one side only), a competitor emerged: the fusion connectors. How do they work? These new connectors are "mini pigtails", that is, they have a piece of fiber inside the chassis that allows us to merge and connectorize at the same time. What do we gain? We avoid acquiring a pigtail (more expensive than a fusion connector) and we do not need a cassette (necessary to protect the fiber of the pigtail), but only a simple "frame" to patch. And we managed to connector in the field with a loss of 0 dB.
By the way, as a general recommendation, we should never forget to clean both the connector and the port of the device. The fiber is very susceptible to getting dirty with dust, leaving the channel obstructed for the passage of light, although it seems clean to the naked eye. Therefore, a good little help is the popular disposable pencils that allow you to clean the connectors in seconds. It's a minimal investment for the huge help they provide.
And in the distribution accessories, what new features are there? The first recommendation is to adapt the capacity of the tray to the application. In broadcast we don't usually require the same high density as a bank's data center. In addition, this would force us to have tiny fingers to be able to patch quickly, which is something basic on television.
There are low-density trays more suitable for LAN networks in the broadcast field. In addition, they usually allow the extraction of the "frames" or "cassettes" (with splice guard) both in front of and behind the rack, or even advance or delay them, without getting them out. With this we gain in accessibility and speed of operation. Another recommendation is that these trays support signal mixing, that is, they can house "frames" for fiber, for CAT cable, for multimedia applications (HDMI, BNC ...) This way we make better use of the available UR.
On the other hand, let's not forget that there are dividers (or "taps"), for signal monitoring. It is a simple, passive accessory, with an input, an internal prism and two outputs, one of which takes a small part of the signal for monitoring, without the need to disconnect the main output.
Finally, we do not forget what was mentioned at the beginning: the "SMPTE" cables. In addition to the traditional division between cables for fixed installation and those for mobile units (called "rough use", which support greater flexibility), SMPTE cables with double indoor/outdoor protection are appearing, useful for sports stadiums.
How do they work? They have been certified by flame tests to withstand a fire, the cable should never be ignited and be responsible for spreading a fire. They can also be outdoors, with a lining that withstands rain and moisture. By the way, another important accessory for stadiums is the famous "breakout", which separates the fiber threads from the copper pairs, which then follow different routes (due to the distance each one supports).
In a next edition, we will talk about the other types of fiber: tactical or military (with poly-urethane lining), energized fiber (with a pair of copper glued to power remote equipment, for example, DAS antennas), fiber with non-metallic dielectric (which is not necessary to land, and which provides high-strength protection outdoors), fibers with anti-fungal and anti-rodent protection (for example, for GPON projects in hospitality), etc.
For more information, you can write to Juan Cortés, Belden AV, at the mail [email protected]
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