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, traditionally we usually 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.

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However, once the SMPTE 2110 standard for uncompressed broadcast signal over the IP protocol was recently approved, terms like "broadcast datacenter" are starting to appear, where IT and AV promise eternal love. And, as often happens in every marriage, the parties must accommodate their respective interests with as little discussion as possible.

How is the bandwidth of a video signal over IP calculated? We multiply the resolution (horizontal x vertical) by the number of fields per second. The result is multiplied again by the color depth (are we sampling 8 bits, 10 bits, 12 bits?), And finally 3 (RGB). If we do a conservative calculation, we will realize that it is dangerously close to the 10 Gigas per second (just the parameter of the CAT6a cable).

Therefore, with the 4K trend, it is fiber that is taking over from copper in television signal production environments. As you know, fiber optics can handle the 40 Gigas 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 singlemode) as well as the type of connector (LC, SC, ST ...) . What we need to 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 that modulates the information at a specific wavelength to this fiber (1310 and 1550 nm) circulates.

How easy is fiber optic breaks? The current ones of certain quality endure quite a lot of abuse before breaking down. But we must not forget that they have a radius of curvature that we must respect. If we do not do it, the loss that the manufacturer shows in the catalog can be triggered and, therefore, the transducer equipment at destination may not have enough light to "see" any signal.

What about the 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, there was no need to merge the fiber to put a connector.

Effectively this method supposes a certain loss (0.2, 0.3dB ... depending on the skill of the installer) that, nevertheless, supposes 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 patch factoryized on the one hand 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 connect at the same time. What we win? We avoid purchasing a pigtail (more expensive than a fusion connector) and we do not need a cassette (necessary to protect the pigtail fiber), but only a simple "frame" for patching. And we managed to connectorize 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 get dirty with dust, leaving the channel blocked for the passage of light, although it seems clean to the naked eye. Therefore, a good small help are the popular disposable pencils that allow cleaning the connectors in seconds. It is a minimal investment for the enormous help they provide.

And in the distribution accessories, what's new? The first recommendation is to adapt the capacity of the tray to the application. In broadcasting we do not usually require the same high density as a data center in a bank. In addition, it would force us to have tiny fingers to be able to quickly patch, which is something basic in television.

There are lower density trays more suitable for LAN networks broadcast. In addition, they usually allow the extraction of "frames" or "cassettes" (with splice guard) either in front of or behind the rack, or even to advance or delay them, without actually removing them. With this we gain in accessibility and speed of operation. Another recommendation is that these trays support signal mixing, that is, they can accommodate "frames" for fiber, for CAT cable, for multimedia applications (HDMI, BNC ...) Thus we take better advantage of the available URs.

On the other hand, do not forget that there are dividers (or "taps") for signal monitoring. It is a simple, passive accessory, with one input, one internal prism and two outputs, one of which carries 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 "heavy duty", which support greater flexibility), SMPTE cables with double indoor / outdoor protection, useful for sports stadiums, are appearing.

How do they work? They have been certified by anti-flame tests to withstand a fire, the cable should never be ignited and be responsible for spreading a fire. They can also be in the open, with a lining that holds rain and moisture. By the way, another important accessory for stadiums is the famous "breakout", which separates fiber strands from copper pairs, which then follow different routes (due to the distance each one supports).

In the 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 feed remote equipment, for example, DAS antennas), fiber with dielectric not metallic (that is not necessary to land, and that grants protection of high resistance in exterior), fibers with anti-fungal protection and anti-rodents (for example, for GPON projects in hotels), etc.

For more information, you can write to Juan Cortés, Belden AV, at the email juan.cortes@belden.com

Richard Santa, RAVT
Author: Richard Santa, RAVT
Editor
Journalist from the University of Antioquia (2010), with experience in technology and economics. Editor of the magazines TVyVideo + Radio and AVI Latin America. Academic Coordinator of TecnoTelevisión & Radio.

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