Articles and whitepapers

Cabling for HDTV (4/9/2006)

By Jonathan Rigby, Asheridge Communications

The launch of Sky High Definition (HD) has seen custom installers faced with the issue of cabling houses and future proofing them for HD. Basic installs have historically used a video distribution amplifier (typically known as a loftbox) to combine TV, CCTV, video and satellite around a property. The output of the Sky box has been fed into the distribution amplifier and distributed to multiple viewing points, potentially of varying distances from the set top box. With the advent of HD, this method of distribution needs reassessing.

Digital superseding analogue

The output of a set top box typically has a High-Definition Multimedia Interface (HDMI) output, and content can be protected using High-bandwidth Digital Content Protection (HDCP). This then requires some sort of HDMI to HDMI cable to connect the source to the display. Today, Sky is allowing the custom installer to connect source to display using the unprotected analogue component connections. The delay in activating the HDMI output on the current Sky box is due to the fact that HDMI is an evolving standard and that Sky did not want its customers to be stuck with an obsolete box that might not offer the latest HDMI spec of v1.3. This article is written on the basis that in the future, the 1080p and higher resolution HD output of the box will be HDMI only.

Standard HDMI cable

Other media sources, including HD-DVD and Blue-ray players, will 'down-rez' analogue 720p and 1080i to 480p on the component outputs, leaving 1080p the mandatory HDMI standard. That seems fair enough since most consumers don't yet have 1080p displays or sources.

Cable lengths

The biggest challenge for an installer is the distance between source and display. Using a standard copper HDMI cable, the distance it can transmit HD depends on the resolution being used (720p, 1080i, 1080p etc). The HDMI organisation has qualified cables to varying distances based on the standard and suggests no longer than 15m at 720p or 1080i. Others in the industry have suggested that at 1080p, 8m is the maximum length recommended for copper. If the resolution of content increases beyond 1080p, then the distance copper can be relied on will reduce. So what are the alternatives?

Where the resolution is 720p or 1080i, we have seen a number of installers use copper cable repeaters to gain the extra metres, up to 30 metres maximum. These cannot be viewed as a long-term solution if higher resolutions are used. Long distances of copper cables fitted and plastered behind walls will not fully future-proof the client's property. Above these distances, two main solutions are available: Cat5e and fibre.

Cat5e

The Cat5e-based solutions use two Cat5e cables with a transmitter one end and a receiver at the other. These solutions can extend the signal up to 60 meters at 1080i, but this drops to 45 meters as the resolution increases to 1080p. It can therefore be seen that as resolutions continue to increase in future, distances will decrease with this copper-based solution.

Fibre

Fully future-proofing a property for HD distribution requires a solution that can deal with the large bandwidth (Gigabit) of an HD signal. The adoption of a fibre optic-based solution is the most obvious one due to its bandwidth capabilities in comparison to other transport methods. Fibre will ensure that 1080p and above can be distributed between source and display.

Fibre solutions tend to come in two flavours; modular and integrated. The first is a fully-integrated solution. The HDMI plug has a converter built into it and it transmits the HD signal over fibre and the HDCP over a copper.

The second one is modular, and has a four core fibre, terminated with LC connectors running alongside a CAT5e cable. In both cases, Cat5 is still used for the HDCP, DDC (Display Data Channel), and 5V power requirements, running parallel to the fibre cables.

Modular fibre solution with terminated with LC connectors running alongside a CAT5e cable

Installation issues

Moving on from the technical differences, most installers are concerned about the ease of install and the costs of each solution.

One of the most common issues faced by installers of the digital interface is the size of the HDMI plug and pulling it through the walls. This is made more difficult when faced with a Digital Video Interface (DVI) connector which is larger still. Unlike other AV connectors, there is no option to terminate a copper cable with an HDMI plug in the field, thus allowing the installer to pull through the cable on its own.

If the cable run will not allow for a cable with a plug on it, a preterminated fibre with connectors staggered and fitted in a pulling sock can be used. On the shorter distances, or where there are no concerns about higher resolutions, Cat5-based systems can be employed. As discussed above, at either end, both will plug into their respected transmitters and receivers. If space is not an issue and the distances short, then there is no problem installing a standard copper cable, or better still, on longer runs, the premade fibre cables with HD plugs already fitted.

Costs

Given an open-ended budget, it would best to employ fibre throughout the property to fully future proof it. The price of a 10m integrated fibre solution is GBP210, which compares very reasonably with some of the high-end copper solutions. However, a good quality HDMI organisation-approved 10m cable should not cost more than GBP40. Where distances are above the 15m, but below 45m, the difference between Cat5 and fibre is minimal, but remember, fibre has the performance advantage for the future.

Final advice

Just as with copper, there are different grades of fibre. Be sure to use the best, not the cheapest. The bend radius must be 1" and the fibre should be glass-based, not plastic. Always remember to test the connection outside the walls before installing through the wall. Your cable installation, if done with proper care, should last ten years or more.

Jonathan Rigby MBA, MSCTE is the Sales and Marketing Director for Asheridge Communications Ltd, supplier of a wide range of installation products and solutions aimed at the custom installer.

www.ashcomms.com