special report fibre optics
New requirements in the industry are driving broadcasters to embrace fibre. As new facilities are built and older ones upgraded, broadcasters are implementing HD at both 1.5 Gb/s and 3 Gb/s data rates. At these high data rates, coax installs need to be augmented with fibre to accommodate all necessary path lengths. Stan Moote, vice president of corporate development at Harris Broadcast Communications, reports.
Fibre optics: 5 points for success
P
ractically speaking, coax is really only good for 60m maximum (by the time one includes connectors, patches and some overhead for non-
standard/emergency patching). Even within a central equipment room, seemingly short distances are chewed up very quickly in the facilities’ cable trays. And, meeting SMPTE 424 specifications becomes more difficult as inexperienced installers often squeeze the coax with incorrect tray loading or tie wrapping.
Given these factors, more and more broadcast products now offer fibre interfaces. These interfaces make a mixed-mode plant - one incorporating both types of fibre, single-mode and multimode - feasible now that products such as
A full line of physical layer optical test
products. The fibre identifier (centre) is a unique tool that clamps onto a fibre cable and identifies both the direction and signal presence without disconnecting the fibre. The handheld OTDR (right of centre) determines fibre cabling faults. The optical power meter and visible laser source (two units on the left) are crucial tools for any technician’s kit.
A/V processors, up/down/cross converters, frame synchronisers, multiplexers/demultiplexers, and distribution amplifiers offer optical. Furthermore, mid- and large-size routers now offer user-customisation of the I/O for coax or fibre by simply changing out I/O modules to provide the required quantity of optical ins and outs.
Although learning about fibre optics is considered by some as a scary and tedious task, practically speaking, it isn’t. All you need to learn are five simple points - master these and you’ll be surprised how comfortable you are using fibre.
Fibre modes
Although both single-mode and multimode fibre types are available, it’s best to keep it simple - use single- mode. Multimode limits the distance, even within a large building. Single- mode enables you to go for kilometers without calculating a link budget.
It’s also important to understand that fibre has another unique characteristic over coax - multiple cables in a single jacket. With fibre counts of 6, 12, 24, 48, 72 and 96,
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install costs go down, and you create instant flexibility. For example, consider a studio that has four outputs, two returns and house black yielding seven feeds. The plant designer drops in a 12-count fibre. Six months later, this room is needed for a sudden pop-up 1080p event. The solution is simple - wheel in a second switcher, and suddenly you’re up and running without laying cables! And your install time is cut in half. Please note that installation crews need to know the proper method for installing fibre to ensure that it doesn’t crack. It’s critical to know the cable specifications for the bending radius, as bending cable too sharply is your worst enemy in the optical world. When you check the cable specifications, you will find the bending diameter is typically 40mm; however, there are newer cable types that allow for bending as low as 15mm. Also, make sure to note the crush tolerance, so as to avoid too many cables on top of the fibre and, as in coax, avoid incorrect tie- wrapping. • Point 1: Use only single-mode fibre, install more than you require, and know the fibre bending radius specifications.
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