It was at NAB in 1970 that television production took a huge leap forward. Philips and Norelco (its US operation) introduced a new three-tube camera, the PC100. Although this showed significant improvements in picture performance, the big news was the way that the camera was connected to its base station.
According to the brochure, one of the features was “triaxial camera cable – automatic compensation up to one mile”. This was the first commercial product to use triax, a new sort of interconnecting cable developed by CBS Labs with the support of Philips in Breda (now part of Grass Valley).
Prior to this, camera cables were hugely bulky multicores, capable of only a limited run. Triax was relatively light and flexible, but also electrically robust enough to offer long distance connectivity.
That first brochure says triax “weighs one tenth that of standard colour cable. Its cost is proportionately even less. But the big saving, month after month, is in reduced installation and cable maintenance cost.”
The claim in 1970 that the signal was good for a mile (1.6km) compares well with today’s products. 2013 specification sheets also talk about 1.7km as the range of some newly developed triax at 3Gb/s, depending on the lens and viewfinder type.
Triax is both rugged and flexible, which is an important consideration. In the studio, as cameras move around on pedestals, the camera needs to follow freely, putting up with being buffeted by other cameras and equipment on the studio floor.
On outside broadcasts the cable needs to be strong enough to survive being literally pulled in, often across rough terrain. It also needs to provide good protection from the elements, as sports television goes ahead in all weathers.
Perhaps the most extreme example is in ski racing where cables are laid at the beginning of the winter and may spend months beneath metres of snow before they are needed.
All in all, the advantages were huge, and triax was widely adopted as the open standard for connecting cameras. This, in turn, meant that venues which regularly hosted outside broadcasts, like sports arenas, installed triax cables between the camera positions and the location of the OB truck.
It meant that any broadcaster and any OB company could turn up and save the rigging time of pulling in cables.
When television moved to HD it was found that, with good quality cables and connectors, triax still stood up pretty well, meaning there was no need for a major reinvestment. But there was some concern that triax would not cope, and so investigations were started into newer technologies.
At this point it is worth remembering that the camera video signal is far from the only thing that passes down the triax. Camera control signals and tallies are sent from the base station to the head.
There is return video to help the operator line up the shot against another camera, and there is two-way intercom. Finally, there is the 100V dc power required by the camera. All these are multiplexed on the triax, and any replacement needed to do the same thing.
Article continues on next page ...
The solution was a hybrid fibre cable. This includes two single-mode fibres, two signal cables, along with four substantial conductors to carry the power.
Although this used off-the-shelf fibre technologies, the addition of the power conductor made it a special purpose system, although this is now defined as SMPTE standard ST 311:2009 (originally SMPTE 311M) so the same benefits of standardised connectors and cables apply.
The design of the system took into account the hard life that outside broadcast camera cables, in particular, have to put up with so the fibres are protected as far as is possible. Range of SMPTE triax is typically around 5km from camera head to base station or repeater.
The choice of two single-mode fibres gave it more capacity than triax, for instance offering two full HD return video channels, increasing operational flexibility.
More recently, a new development has arrived. Rather than using the specialised, SMPTE fibre, the intention behind this is to use the standard, off-the-shelf single mode fibre in common use in the telecoms industry. Grass Valley was first with the idea, developing a multi-fabric approach to camera connectivity. Other companies, including a number of specialist fibre vendors, have joined in.
The advantage of using telco fibre is that it is lighter and less expensive than SMPTE cable. The most obvious disadvantages are that it needs interface boxes at each end, and it means running a separate power and signal supply to the camera head.
So which is best for camera connectivity: triax, SMPTE fibre or standard telco fibre, perhaps in multicore. The answer is clear: it depends on what you want to do with it.
Where you have an existing triax installation, or a big investment in triax cable, then that is likely to provide the best solution for a long time to come. It supports today’s HD signals, including triple speed super slow motion cameras. It is great in dusty and dirty environments, and is easily maintained leading to low cost of ownership. The downside is the limited reach.
If you need extra-long permanent cable runs, then a customised system using telco style multicore fibre could provide the extended range and be cost effective.
An outside broadcast truck that spends much of its time at football grounds, for example, would probably remain triax or SMPTE, depending on what is installed at the majority of grounds in the territory. If for one week a year it covered a golf tournament, then you could use telco fibre to reach the back of the course.
The really critical issue is that, whatever fabric you need, the cables and connectors you choose are appropriate for the job. As I said earlier, reliability and ruggedness are absolutely central to your choice. Cables, particularly on outside broadcasts, have a hard life. They must stand up to being dragged across uneven ground, and must cope with rain, mud and snow.
Fibre, in particular, is inherently delicate. Single-mode fibre is a strand of glass 9 microns in diameter: an order of magnitude smaller than a human hair. The casing has to protect that narrow fibre. Connectors and caps have to seal perfectly: it does not take much dirt to block an optical path just 9 microns across.
Choose connectors which are designed to work with the specific brand of cable you choose. Despite triax, SMPTE fibre and telco fibre all being designed around well-established open standards, there are mechanical differences.
Finally, whether you choose pre-assembled cables, customised systems or want to make them yourselves, talk to a cable specialist who can give you the best advice on what will work for your application. Companies like Argosy live and breathe cables and connectors, and our reputation depends on your signals staying perfect.
Josh Simons is technical director at Argosy.