Cabling for the Future
As the broadcast landscape continues to evolve, infrastructural needs of broadcast facilities have changed drastically. A critical part of this infrastructure is the cable. Josh Simons takes us through what modern cabling entails
For so many years, cabling in a broadcast installation was all about co-ax. The art was to choose the right co-ax, which gave the performance you needed, at a cost which met your budget. Then you teamed that with matching BNC connectors and your decisions were made.
Today, the situation is rather more complex. Fibre is increasingly providing the SDI connectivity, and that brings both huge benefits and new challenges. More recently, Ethernet over twisted pair has become very significant, as interest has grown in IP connections.
The result is that many systems engineers are now faced with installing all three cable types, and I will look at each in turn. It is important, though, to remember what they have in common in our industry.
We are tough on our cables. Even installation cables in the backs of racks tend to be handled much more than in other branches of industry, because we change our equipment configurations much more.
At the front end of the business, around production, cables have a very hard time. Camera and microphone cables are routinely dragged around the studio floor, or literally pulled in over long distances on outside broadcasts.
So it is really important that you choose the right cable for the task. If it is a cable that is going to be handled, ensure it is ruggedised, and if it is going outdoors then use a dedicated solution for harsh environment. Cable failures can cause significant loss of time on a production, and are disastrous on a live event, so choosing the right cable is important.
In the machine room, there will still be a lot of patch cords in use. These again have very special characteristics. Flexible jackets allow the cables to be pushed aside, but the connectors need to be plugged and re-plugged a lot so a good tight bond to the cable, which does not put any stress on the cores, is vital.
Incidentally, while the general view is that fibre optics are inherently fragile, patch cords have been a practical proposition for some years now, with many G657A bend insensitive single mode fibre cables becoming readily available. As always, choosing the right cable for the job is vital.
IP signals travel over Ethernet cables, which are surprisingly simple. They use the very old principle of the twisted pair: one cable has a positive voltage, the other a negative, so any interference should be cancelled out. The result is that even high-speed data signals are amazingly robust on what appears to be a very simple cable.
When shopping for an Ethernet cable, you may see the abbreviations UTP and FTP. UTP simply stands for unshielded twisted pair, the most common form of Ethernet cable. It provides very high speed performance, including Cat 6 Ethernet, which provides the gigabit speeds we need.
FTP means foil-shielded twisted pair. For our applications, this is usually an aluminium-laminated plastic foil which provides an extra layer of electrical protection. More important, perhaps, this together with the rugged jacketed cables provides more physical protection to the cable for outside broadcast applications.
Multicore IP cables are available for installations, and as with any cable it is really important to choose suitable matching connectors. You need to consider if this is a permanent connection or if there will be regular plugging and unplugging, as well as the best electrical matching.
We are seeing a rapid increase in the use of tactical fibre, particularly in outside broadcasts. Cables can contain as many as 24 fibres in a single cable, which with multiplexing means that many signals can be carried down one cable.
That is particularly important on outside broadcasts such as music festivals and major sporting events, where the time to rig and de-rig is a significant cost factor. Being able to do everything on one or two tactical fibres is a real time saver.
On the other hand, these cables can be prone to damage, so riggers need to be trained in how best to handle them. Breaks, should they occur, tend to be at the connector or in the last metre.
Ultra HD and more
Over the last couple of years, there has been a great deal of interest in higher resolutions than HD, 4K and even 8K. The problem for those wanting to implement them is that there has been no standard for interconnections. Each vendor has chosen its own route.
Now we are in the happy position of clearly defined SMPTE standards, covering both copper and fibre cabling for high resolution signals. In particular, we have a clear definition of how to handle signals up to 12 gigabits a second.
This is important, because it allows vendors to develop standard interfaces for their products, such as cameras, switchers, routers and servers. It also allows the test and measurement specialists to develop appliances which can accurately evaluate equipment and systems: Tektronix, for instance, launched such a device at NAB this year. That, in turn, allows cable specialists to determine precisely what can be achieved using different cables.
We are waiting for the new generation of test equipment to make our own evaluations, but what the major cable manufacturers like Draka and Belden are telling us is quite surprising. It looks like appropriate co-ax copper cable will be able to carry 4k video over distances of 100m or more.
All this points to the future of cabling being much the same, which is a hybrid mixture of SDI over copper and fibre and IP over Ethernet. And as ever, the best advice on choosing the right cable and connector is to talk to an expert who has thoroughly tested, measured and evaluated the products on the market and can recommend the best products for the job in hand.