Considering cables

Best practices to consider when choosing and installing cables.
Fibre Optic Cables.
Fibre Optic Cables.

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If you are building a new video installation, or modernising an existing infrastructure, you will at least have in mind 3Gb/s capabilities.

You may not need 1080p HD at the moment – you may not even need HD yet – but it does makes sense to build to the highest quality now, knowing you are ready when the time comes.

With that in mind, you have to ask yourself a fundamental question. Is it time to move to fibre optics, or can we stick with the co-axial copper cable that we have known and loved for so long? As always with questions like this, there are good arguments on both sides.

Firstly, you need to invest in the very best quality cable – but you also need to change installation practices. For instance, you must avoid sharp bends, so no more neat wireman work with every cable brought out tidily to side rails.

Crushing the cable with a tie will dramatically alter its impedance performance, which may well mean that the signal does not get through. Even with the best cable and installation, and the latest generation equipment at either end, distances between devices will be no more than 100m and quite probably less. That can be a challenge for system designers, too.

Unless you really mistreat it, fibre does not suffer from crushing forces, and distance is effectively no object.

Yes, there is a minimum radius for curves (unless you use one of the new, highly flexible fibre cables like Argosy’s BendBright, designed for jobs like patch panels) but otherwise you can route fibre anywhere you want to.

And the clinching argument may be that fibre by the drum is now cheaper than the high quality copper co-ax you need for 3Gb/s installations.

On the other hand, there is as yet no fibre equipment. Every time the signal goes into or out of a device, you need an optical/electrical interface.

These cost money, draw power and emit heat. The additional heat – which can build up over hundreds of inputs and outputs – means more air conditioning. So the capital saving in fibre may be counterbalanced by the equipment and the operational cost of the extra power.

Every engineer knows how to fit a BNC connector onto co-ax cable, and it can be done with tools that are extremely inexpensive and readily available. That is not the case for fibre.

A single mode fibre optic cable is a strand of glass 9 microns in diameter – finer than a human hair, and finer than much of the dust found in the typical machine room.

So while putting a termination onto a co-ax cable is a 30 second job on site, because of the need for a perfectly dust-free atmosphere, terminating a fibre has to be done in a clean room. The minimum investment in that sort of clean room is going to be the equivalent of around US $150,000.

For practical purposes, optical connectors are sold ready fitted to short tails of fibre, to be spliced on site.

You need a special tool called a core alignment splicer, which brings the two pieces of fibre – cable and terminator tail, in this case – together and aligns them perfectly. It fuses the two together, then performs a mechanical stress test. The results should be highly reliable.

There are a number of splicing machines on the market. The good quality device that we would recommend is around $10,000. In comparison with a set of strippers that seems like a lot of money, but it is a sensible investment and, over time, may not be seen to be a significant cost.

The splice, incidentally, provided it is made properly by an accurately aligned machine, causes virtually no attenuation of the signal.

While you would not want to put a joint in co-ax mid-run, you can certainly repair fibre should it break. Indeed, some argue that when making the installation you should lay in some spare fibre so that you have slack if you ever do need to repair it.

To sum up, then, copper is widely understood by all broadcast engineers, and can be installed with simple tools, but it needs careful physical handling and is limited in range.

Inside the facility, fibre has no restrictions on path length and is unlikely to suffer from signal degradation, but the chances are the engineer will need new training as well as relatively expensive tools. The choice is yours.

 

Producers:

Draka
www.draka.com

Draka’s PATCH PRO FLEX Cat.7a is a flexible AWG patch cable specifically designed for interconnecting computer and studio units on stage, within professional studio units and outside broadcast units. This new patch cable is developed in close consultation with Neutrik, a major supplier of professional entertainment connectors.

“For the investments that studios are making in today’s workstation environments, it is essential that the patch cable is one of the most reliable links in the chain, both physically and for data transmission quality,“ commented Oli Hentschel, product manager, Studio Broadcast.

“We have designed and produced the Patch Pro Flex with this level of technical sophistication in mind so that it is guaranteed to meet the highest level of professional expectations for digital transmission.”

The design of this new patch cable consists of a single, highly flexible outer jacket and an increased size inner conductor of stranded 0.14mm twisted 2-core copper wire to increase performance while reducing attenuation.

Draka has paid attention to a unique construction that makes the patch cable suited for stage, studio, as well as outside broadcast applications. The new patch cable is constructed of PIMF Plus tinned braid and a robust black outer jacket made from a flexible Polyurethane of 6.4mm diameter.

This combination offers a high degree of robustness as well as high resistance to extreme temperatures and weather conditions.

Patch Cable PRO FLEX Cat.7a is suitable for Video Ethernet IEEE 802.3, 10Base-T, 100Base-T, 1000Base-T (IEEE 802.5 16 MB), ISDN, FDDI and ATM. It conforms to ISO/IEC 11801 and IEC 61156-6 specifications.

Belden
www.belden.com

Belden will showcase several cables including the 26 AWG shielded twisted pair HDMI cables in lengths of 1, 2, 3, 4, and 7 metres.

To demonstrate the unique cable performance properties of these HDMI cables, Belden has successfully run an unamplified 1080p/60 digital video signal 30 metres from a generic Blu-ray Disc player to a generic 1080p/60 display. The result is a crystal clear 1080p/60 digital video signal over 30 metres.

Even when the cable is flexed or bent, the conductor-to-conductor spacing remains constant. This means that the impedance also remains constant, and the problems of regular twisted pairs, such as impedance variations, are minimised. Impedance variations cause signal reflection (“return loss”).

These variations also allow the signal to radiate off the cable (egress) and to pick up noise from other sources (ingress). Reducing these effects allows cables made this way to run farther, with less signal loss, and less noise, than regular twisted pairs.”

In addition to making bulk cable with Bonded-Pairs, Belden also produces standard nonbonded-pair HDMI cables as assemblies.

Belden’s HDMI cables are also performance tested to verify their capability to handle transmissions in advanced high definition applications based on 1080p. These digital video/audio cables are also UL-rated for residential and commercial installations (including in-wall use).

Mike Purnell is the director of Argosy Cable.

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