In Broadcast - October 2012 - 48


I N T E R N A T I O N A L

N E W S

WWW.INBROADCAST.COM | ISSUE 13 - OCTOBER 2012

InTECH

Making The Fibre Connection: Catching The Light Waves
By Gordon Kapes, Studio Technologies
The world of fibre transport of video and audio signals is all around us, with production after production coming alive essentially through an optical fibre-connected broadcast chain. Factors such as transmission over longer distances, immunity from electromagnetic interference, no crosstalk between cables and the ability to carry higher bandwidth signals are all reasons why the industry has turned to fibre and away from copper. Following the three simple installation and deployment practices outlined below combined with having the necessary devices in the tool kit to clean, test and troubleshoot will make any fibre setup catch the light waves. With fibre, connector cleanliness is next to signal godliness. With transmission wavelengths measured in nanometers (nm), a dust or dirt particle measured in microns might look like Mount Everest to an optical device, while something as innocent as skin oil coming in contact with a fibre end can act like a pair of very dark sunglasses. In both cases the contamination can greatly affect the transmission of optical signals. The first practice, therefore, for reliably and consistently catching the light wave is making sure that the appropriate optical connector cleaning devices are part of every on-site maintenance kit, along with the consistent practice of cleaning each fibre interconnection before use. Something as simple as an optical paper wipe can be sufficient to clean the actual fibre end (the “endface”) of a connector. Other options include cartridge-based systems that have a push button device that feeds the next wipe, “one use” wands for cleaning inside connector housings and low-cost optical cleaning sticks. The second and third items for the fibre tool kit deal with the actual transmission of light through the fibre, so now might be a good time to discuss signal loss as a function of distance. The industry tends to describe the capability of fibre-connected equipment in terms of distance, usually in kilometers (km), which is convenient but not technically descriptive. Most equipment offers a distance specification of at least 10km (6.2 miles) which, on the face of it, would typically be more than adequate for most broadcast applications. However, the question becomes 10km under what conditions? While pristine, carefully maintained fibre might work for that distance, a more realistic scenario of possible dirty connections, poor splices with high signal loss, or sharp turns/kinks along the fibre path are some of the factors that really dictate the maximum interconnect distance. A more accurate specification, known as the Optical Power B u d g e t (O PB) stated in dB, is a better way to determine the ma ximum acceptable reduction in optical power over an interconnecting fibre path. For example, if a fibreinterconnected system, such as the Studio Technologies’ Live-Link Jr. Remote Camera Interface System, states an OPB of 14 dB and the total optical signal loss (attenuation) over the specific fibre run is only 6dB, everything should work properly. If, however, the signal loss is greater than 14dB, the receiver circuitry will literally not be able to “see” the transmitted signal. Worse, where the signal strength is just on the OPB edge, the receiver might work sometimes and not others. Looking at maximum allowable signal loss, rather than distance, gives a technical team a much better perspective on what is going on. The second recommended set of devices for the troubleshooting “kit” consists of three simple items: visible light source, a more sophisticated single-mode optical power light source and an optical power meter. The visible light source produces an optical signal, typically red in colour, which can be detected by the naked eye. It allows a rapid confirmation that a fibre has continuity. It’s a quick initial go/nogo test to be certain that the fibres you want to use have the potential of serving the application. If everything is a “go,” the next step would involve the single-mode optical light source and optical power meter. The light source, connected at one end of the fibre run, produces an optical signal at a single (fixed or selectable) wavelength at a constant power level (brightness). The power meter connected at the other end of the fibre measures the amount of light coming through, displayed in dB. If the measured value is significantly less than the OPB of the equipment to be connected then everything should be okay. If more than the OPB, the equipment won’t function. With the recent release of higher-performance equipment, it’s common to find optical multiplexing, or sending multiple wavelengths of light down one fibre, being used. That is when troubleshooting gets tricky. Some broadcast applications employ a technique called C o u r s e Wa v e Division Multiplexing (CWDM) where up to 18 unique wavelengths (light “colours” or frequencies) can be sent over a single optical fibre. While all 18 wavelengths are almost never used, having two (often 1310 and 1550 nm) or three (1310, 1490, and 1550 nm) is becoming common, with four and eight wavelength installations no longer rare. With this added complexity, the need to measure optical power at specific wavelengths becomes important to insure a properly functioning system. While laboratory optical spectrum analysers perform wonderfully with observing CWDM signals, their cost can easily run to $50,000 and beyond. Fortunately a new class of affordable wavelength-specific power meter devices has become available. These provide a direct
Gordon Kapes

48

display of the power (in dBm) of the CWDM wavelengths. As a practical example, if a fibre run has a tight bend or “kink” in it, the optical energy at 1310 nm may incur little loss, but the energy at the longerwavelength of 1550 nm could attenuate much more and prevent correct equipment operation. An optical spectrum analyser (or the less-costly alternative) can detect this wavelength specific deficiency saving an astounding amount of time troubleshooting the entire system. An example of contemporary equipment is the Studio Technologies’ Model 400 SDI-over-fibre transport systems that use 1310, 1490, and 1550 nm optical multiplexing to send multiple SDI video signals over one fibre. Having a wavelength specific optical power meter makes quick work of confirming that Model 400 units and associated fibres are functioning properly. The odds are great that any particular fibre setup is working on the edge of acceptable optical margins, especially in the case of portable application. Spending money upfront on the proper tools to clean, test and troubleshoot will pay off in more efficient deployment, reduced troubleshooting time, and ultimately less stress for the tech team. ■

A tight bend in fibre brings the 1550nm below the threshold level


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Table of Contents for the Digital Edition of In Broadcast - October 2012

In Broadcast - October 2012
Contents
PO Group Invest in 4k SGO Mistika Solution
BBC Entertainment Launches in Malaysia
AJA KI Pro Eases Elton John Show Workflow Transition
Bolshoi Theatre Install RTS System
Canal+ Sports Opts for Orad Power Wall
SIS LIVE Rolls Out OB 14 HD Truck
OCC’s Bill Smith Answers on the Technical Challenges
4KTV? Not So Fast!
ChyronIP Powers Graphics on Newtek Tricaster
Take Control With Rascular’s Helm
In Broadcast - October 2012 - Intro
In Broadcast - October 2012 - In Broadcast - October 2012
In Broadcast - October 2012 - 2
In Broadcast - October 2012 - Contents
In Broadcast - October 2012 - PO Group Invest in 4k SGO Mistika Solution
In Broadcast - October 2012 - 5
In Broadcast - October 2012 - BBC Entertainment Launches in Malaysia
In Broadcast - October 2012 - 7
In Broadcast - October 2012 - 8
In Broadcast - October 2012 - 9
In Broadcast - October 2012 - 10
In Broadcast - October 2012 - 11
In Broadcast - October 2012 - 12
In Broadcast - October 2012 - 13
In Broadcast - October 2012 - 14
In Broadcast - October 2012 - 15
In Broadcast - October 2012 - 16
In Broadcast - October 2012 - 17
In Broadcast - October 2012 - 18
In Broadcast - October 2012 - 19
In Broadcast - October 2012 - 20
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In Broadcast - October 2012 - 23
In Broadcast - October 2012 - 24
In Broadcast - October 2012 - 25
In Broadcast - October 2012 - 26
In Broadcast - October 2012 - 27
In Broadcast - October 2012 - 28
In Broadcast - October 2012 - 29
In Broadcast - October 2012 - AJA KI Pro Eases Elton John Show Workflow Transition
In Broadcast - October 2012 - 31
In Broadcast - October 2012 - 32
In Broadcast - October 2012 - 33
In Broadcast - October 2012 - 34
In Broadcast - October 2012 - 35
In Broadcast - October 2012 - 36
In Broadcast - October 2012 - 37
In Broadcast - October 2012 - Bolshoi Theatre Install RTS System
In Broadcast - October 2012 - 39
In Broadcast - October 2012 - 40
In Broadcast - October 2012 - 41
In Broadcast - October 2012 - Canal+ Sports Opts for Orad Power Wall
In Broadcast - October 2012 - 43
In Broadcast - October 2012 - 44
In Broadcast - October 2012 - 45
In Broadcast - October 2012 - 46
In Broadcast - October 2012 - 47
In Broadcast - October 2012 - 48
In Broadcast - October 2012 - SIS LIVE Rolls Out OB 14 HD Truck
In Broadcast - October 2012 - 50
In Broadcast - October 2012 - 51
In Broadcast - October 2012 - 52
In Broadcast - October 2012 - 53
In Broadcast - October 2012 - OCC’s Bill Smith Answers on the Technical Challenges
In Broadcast - October 2012 - 55
In Broadcast - October 2012 - 4KTV? Not So Fast!
In Broadcast - October 2012 - 57
In Broadcast - October 2012 - 58
In Broadcast - October 2012 - 59
In Broadcast - October 2012 - ChyronIP Powers Graphics on Newtek Tricaster
In Broadcast - October 2012 - 61
In Broadcast - October 2012 - 62
In Broadcast - October 2012 - 63
In Broadcast - October 2012 - Take Control With Rascular’s Helm
In Broadcast - October 2012 - 65
In Broadcast - October 2012 - 66
In Broadcast - October 2012 - 67
In Broadcast - October 2012 - 68
In Broadcast - October 2012 - 69
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In Broadcast - October 2012 - S1
In Broadcast - October 2012 - S2
In Broadcast - October 2012 - S3
In Broadcast - October 2012 - S4
In Broadcast - October 2012 - S5
In Broadcast - October 2012 - S6
In Broadcast - October 2012 - S7
In Broadcast - October 2012 - S8
In Broadcast - October 2012 - S9
In Broadcast - October 2012 - S10
In Broadcast - October 2012 - S11
In Broadcast - October 2012 - S12
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http://europe.nxtbook.com/nxtbooks/lesommet/inbroadcast_APAC03
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