Tuesday, October 27, 2015
User Guide: Fibre for broadcast
Argosy's Josh Simons offers up an in-depth guide to designing and supporting fibre in a broadcast environment
Fibre is now a standard part of the broadcast infrastructure. Today most installation and maintenance engineers are familiar with fibre, although there is still concern that it is somehow more complicated to work with than copper co-ax.
First, we should define what we mean by fibre relevant to the broadcast industry. There is the SMPTE camera cable, which is a tightly defined structure containing a pair of fibres for the signals and two pairs of copper for signal and power.
The vast majority of fibre failures happen either at the connector or within a metre or so of it.
We then have “tactical” fibre. This is simply a multi-channel transmission medium, which can carry any signal from point to point. The design is focused on robustness to meet the requirement for repeatable deployment and recovery in harsh environments. Finally there is “dark fibre” which is installed for redundancy and for future expansion.
It is the capacity of fibre that means we should change the way we design cable runs and deployments. We have to try to forget the heritage, and not simply replace copper with fibre. As well as being more cost-effective, this will make for a more reliable, rugged installation. It will also help with future expansion and the inevitable maintenance, so the cost savings are likely to continue.
An obvious conclusion
We spend a lot of time talking to broadcast installation engineers and systems integrators, and from all our research we find that the vast majority of fibre failures happen either at the connector or within a metre or so of it. This is an obvious conclusion if you think about it.
Connecting fibres means pressing the two end faces of the glass together tightly, and this inevitably creates wear. If you introduce dust or other contaminants when you connect the fibres, then the wear is even greater. The part of the cable installers handle is near the connectors, so this is the area which is most likely to get damaged.
For standard installations, use a dedicated multi-core distribution cable. This can be broken out in a termination tray with a patch panel. When planning the installation, assume there will be a need for expansion. The cost of multi-core fibres is relatively trivial compared with the cost of re-engineering later, need 4 fibres pull in 12, need 24 pull in 48, you will need them so build in plenty of extra capacity.
Fibre patch cords are readily available and cost very little. We worked with cable manufacturer Draka to develop a high-resilience cable, BendBright, which is very resistant to handling and is ideal for patch cords. They are likely to last for years, but should one fail just throw it away and replace it: the cost is negligible.
The same technique can be used for mobile and temporary installations. The Neutrik OpticalCon system is designed to be a secure and highly reliable connection for as many as 12 fibres in a single assembly. It is a simple push-pull connector to make rigging simple. However if you need more you can have Tactical assemblies with ruggedized breakout and standard connectors up to 24 fibres.
Should a fibre cable be damaged it needs special skills to repair. At Argosy we have made an extensive investment in fibre optic splicing, polishing and termination equipment to provide support for our customers. We can work with SMPTE and tactical fibres in a number of jacket and connections options, to meet the needs of the installation.
To effect assembly and repairs requires high precision equipment and while we can and do take it out to the field to effect repairs, it can be expensive. There is an alternative solution, though, which again makes fibre the modern, practical solution. If the failure virtually always occurs at the connector or in the last metre of cable, make that readily replaceable.
If you are providing fixed SMPTE camera connections, in a sports stadium perhaps, then rather than running SMPTE cable point to point, install infrastructure cable to breakout points near the outside broadcast connection point and camera location. Inside sealed boxes, terminate the cable with a high reliability, telco-standard interface like LC.
Then simply use short SMPTE pigtail assemblies from the box to the panel. If it fails, replace it with another – it will be relatively inexpensive, can be done within moments, and will be cheaper than a field repair. Then return the faulty pigtail to us for repairs.
Fibre has huge technical advantages: it carries higher bandwidth signals over greater distances than copper. Talk to your cable supplier to get the best advice on the right choice of cable, connector and installation practice. The goal is a cable infrastructure that you can install and forget.