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Cabling and Systems for Video Distribution - a Custom Installer's View (1/3/2010)

By Chris White, DK Home Technologies and Wired Life

Hardly an hour goes by on one of the biggest UK consumer electronics forums without someone posting a question about HD video distribution and the automatic assumption that it will use HDMI connectivity. Equally, when I see another low-cost HDMI matrix or switch triumphantly launched by a manufacturer, website or distributor without consideration of issues and the poor consumer who buys it, I am actively turned off the brand or distributor.

The fact is the HDMI interface was only ever intended to be used as an interconnect for local pieces of hardware, and this has got totally lost somewhere along the line. It is certainly not the great 'answer to everything video' so often promoted for distribution throughout the home.

Current trends

Obviously we all see the glut of low-cost HDMI splitters, switches and matrices and they do seem to be very much the 'on trend' item at the moment. The perceived high cost of providing a proper HD/HDMI distribution system because of these low-priced boxes can kill prospective projects stone dead. But how many of us actually spend time to explain the issues to clients?

As we look at other solutions, we get to what I consider to be the first of the acceptable ways to distribute HD video, using a growing range of HDMI-to-RJ45/CAT5/6 converters and matrices. These are at least using a nice generic/agnostic cable type which allows for system and signal evolutions. But again, in what situations are they actually of use to us installers?

Then we get to the newer technologies, which include proprietary systems, fibre, IP (Internet Protocol/Ethernet) and even wireless, but these are still either costly to implement or really unproven in our CI environment, and we all know the true cost of using unproven technology!

For the custom installer (CI) there is one final option: to use more traditional component matrices. Although these are an older technology, they are perfectly capable of passing HD signals and the technology is proven and reliable, which in my opinion is a must for any serious CI with mid- to large-scale installation projects.

Rear view of the Unicam Avatrix 562 HD component video CAT5/6 matrix that distributes component signals up to 300m away to wallplates or modules mounted wherever televisions are to be located.

The issues with HDMI

You are probably reading this as though I am not a great fan of HDMI, but that is not correct. The idea is great, however, as the goals keep moving with each iteration (currently at HDMI V1.4 in Feb 2010), technology is going to continually struggle to keep up. Once the evolution slows down, then our manufacturers will have a chance to develop solutions that will remain stable.

Currently, the biggest issue I see with HDMI distribution is the HDCP/EDID/DDC (High-bandwidth Digital Content Protection/Extended Display Information Data/Display Data Channel) encryption and exchange of information that has to occur between screen and source. Basically, this is a secure handshaking communication between devices that will confirm a number of specification and performance requirements to optimise the size, resolution and audio performance. If any of these messages fail to get through or are corrupted, at best you can get interrupted viewing, and at worst you get no image at all.

With HDMI distribution systems, sharing just one device to a number of different manufacturers' screens requiring different resolutions, sizes and even refresh rates, can cause problems. Hopefully your source will negotiate with all the screens down to the lowest common denominator. If not, it may just give up and not share anything. Coupled with this is the issue that every time a screen joins to view the source, the whole HDCP/EDID/DDC handshake will happen again to reach a common standard.

If the screens are the same resolution and from the same manufacturer, then there may be no interruption to the image. If they are different, then those screens already watching will have to refresh to the new standard, causing them to blank for anything from a couple of seconds upwards. This may not sound like much, but its the time it takes to read the headlines or see a character get shot in your favourite soap! Who can forget the uproar when ITV's football coverage suddenly and unexpectedly cut to an ad break towards the end of the Liverpool/Everton FA Cup match this time last year, missing the 118th-minute winning goal!

This possibility is not acceptable to those of us providing a professional installation service, and as such, we need to either explain it clearly to the client or avoid it all together.

HDMI developments

Some of the new switches and matrices seen at this year's ISE show are offering 'EDID Spoofing' so the blanking time could diminish dramatically. But you still need to have screens with matching resolutions to get the fastest response. The spoofing works because the switch/matrix learns the HDCP/EDID of the screens attached to all of the outputs, so when a screen joins or leaves a specific device, the handshake time is dramatically reduced. There is a chance that this time frame could drop to one that the human eye cannot see, which would be fantastic, and the test bench reports I am hearing are promising. However I have yet to see it working in anger.

The tradestech 8x8 HD Cat5e Matrix Switch that maintains its HDCP connection regardless of source requests from other rooms or zones.

Other technologies are also starting to emerge. Wireless HDMI for example, has appeared, but the frequencies are far too high to realistically use it as a point-to-multi-point distribution method over any distance or through walls.

CI solutions

Several things are key to being able to offer what the client wants: obviously a correct mix of cabling, but also a clear understanding of the client's requirements and budgets, along with a certain amount of education. Even if they do not want or currently need HD distribution, we should still advocate installing a cable structure that allows a clear upgrade path.

To accommodate this, as a minimum we should wire TV points with a coax cable and at least one CAT5/6 cable, however this an absolute minimum, poverty-developer-type specification. As professional installers, we should actually install something like the bundled cables from SCP, Belden and Liberty, which present two CAT5/6 cables and a pair of coaxes in a single jacket. These are becoming so cost-effective as first fix engineers need just one cable pull to each screen location, one route, one cable marker, one back box - almost one reel!

The SCP HNC-8 cable with 2xRG6/U quad shield plus 2xCAT6, in a single jacket.

For A/V signals, one of the coaxes can be used to carry broadcast Freeview signals (including the new Freeview HD services in Switch Over areas) and the other can be used to offer local, in-room satellite (FreeSat or Sky) services. The two CAT5/6 cables can be used for a number of services, however typically, they are used to distribute HD A/V signals from a central hub to screens throughout the property. Depending on the hardware used, you will need either one or both of the CAT cables for HD video and audio, the choice of which will be down to the signals and level of control you need to provide.

There are a number of single RJ45 systems available, but they tend to limit you to specific signal combinations such as stereo audio only, rather than stereo and digital audio for surround sound, or they may miss out on an IR return path for control of either the main matrix or the remote source equipment.

One other service you should consider providing for is a data network connection for streamed (IP) video, either from a local service or from the Internet using services such as BBC iPlayer and YouTube. Most of the major screen brands are now offering network connections for such services, and this is something SCP has considered important as it is now offering a bundled cable with three data cables and two coaxes, all of which you can (just about!) fit into a double UK back box.

Types of CAT cable

Do you use CAT5e or CAT6? Shielded or Unshielded? The cost difference between CAT5 and CAT6 is so little now, that most installers are switching to using CAT6. Its additional bandwidth, although not needed at the moment, will become useful in the future. The argument for shielded is less clear, for certain it can provide a more robust signal at the receiver end, but poorly-installed or poorly-terminated shields can result in the cable performing worse than an ordinary CAT6 cable. Poorly-terminated shields end up working as an aerial and rather than protecting the signals from interference they end up accentuating any interference issue.

Some more enlightened manufacturers and distributors are also recommending not to terminate the CAT5/6 cables into outlets or patch panels but straight into RJ45 plugs. In the case of HDMI distribution, this will minimise the number of physical connections and potential mismatch points, therefore improving communications between devices.

How to use the cables

Without a doubt, I do not currently see HDMI cables as a proper CI solution for HD video distribution. It is just not reliable enough or repeatable enough to be predictable from project to project.

For small-scale systems, provided the blanking/sync issues are clearly explained to the client, HDMI over CAT5/6 matrices offer a perfectly acceptable solution. Personally, I do not like to offer these to a client needing anything above a four-screen system, as above this number several screens are likely to want to watch the same thing. However for four or fewer screens - typically Kitchen, Living Room, Master Bedroom, Study/Dining/Kids Bedroom - it could be argued that at any one time there will only be one screen watching a particular source.

Be cautious though, if there is signal corruption or the runs start to get long, then you may need powered receivers at the screen ends to help with the regeneration of the HDMI signals. Also watch what your source equipment is trying to send. If you don't need the latest HDMI V1.4 spec for 3D TV, Ethernet Connection or Audio Return, then see if you can disable them to free up some bandwidth. Some of the latest matrices and distribution systems seen at ISE were offering 'kill switches' to disable some of these protocols.

On larger-scale systems of more than four screen locations, I would automatically use an HD component video matrix with RJ45 outputs. There are a number of compact and reliable converter devices that connect directly to a source, converting up to 1080P HDMI output signals to a matching component video source, and take care of all the handshaking required by the source. The vast majority of component switches will pass 1080P well over typical house distances without issue, but you will need to watch the level of control, signals transmitted and power requirements though, as these will dictate the need for a single- or twin-cable system.

Conclusion

A well-designed and thought-through system using coax- and CAT6-based cables should serve a home well for the foreseeable future, and if your client is a little paranoid, then offer some dark fibre (unterminated and no active equipment) to at least one point in each room. Even if it is not used currently, with the evolution of data, screens and sources happening so quickly, we could be using it in no time at all.

Just from what has been seen at ISE and talking to industry friends, there are some very interesting solutions for HD distribution to come during 2010.

On-the-fly encoding and distribution is not with us yet, but HD video streaming really will have to be considered for storage and playback. Video servers were and still are considered the preserve of high-end projects, but as our market is so broad technology wise, the likes of PS3s and Apple TVs start to look like attractive and cost-effective play-out devices, and there seem to be some very interesting self-ripping DVD/Blu-ray/NAS (Network Attached Storage) devices coming to the market.

There is also lots of talk about several different distribution technologies. HDMI over IP is available as a point-to-point solution, and there is certainly lots of development for distribution in this area.

In my opinion however, the 'Killer App' I only heard about when researching for this article, is HDMI over coax! HDMI over five coaxes has already been done, but how many homes have that installed? A single coax certainly has the bandwidth, so if this can be done, how many homes have that installed? What a phenomenal opportunity that offers.

Finally, a little known fact that you may have spotted earlier in this article, Freeview HD is real, and hardware is available today for those areas that have switched totally to digital transmissions (www.freeview.co.uk). So don't be too ready to discount the faithful old coax cable from your installs.

Chris White (BEng) is the Technical Director of DK Home Technologies and founding partner of Wired Life. DK Home Technologies is a provider of cost-effective and intuitive home technology systems for homes and businesses. It is also the London, Home Counties and South-East regional partner for the Wired-Life technical consultancy group and retailer.

www.dk-hometech.co.uk
www.wired-life.co.uk