Introduction:

Digital signage is one of the fastest growing applications, allowing audio-video content to be distributed virtually around the world.  Retailing, education, banking, government, restaurant, hospitality and transportation are just a few of the sectors where digital signage has been rapidly adopted.  The typical configuration involves a video server locate at a central office that is used to program, process, schedule and distribute audio-video content to remote client servers via the wide-area network (WAN).  At the local site, a LAN router and client server receive and distribute the content to nearby displays, often via analog audio-video signaling.   Often there are other video sources such as DVD players and cable boxes at the local site, depending on the application. 

The audio-video content is usually transmitted from the client’s equipment to one or more displays in the  form of composite video, S-Video, Component video, VGA, RF, analog audio or digital audio.   From the cabling perspective, dealing with a multiple array of cable types can be costly and impractical and detract from the efficiency and aesthetics.   As much as possible, establishments try to hide the cabling behind walls, ceilings or under floors in order to eliminate clutter. 

This article compares the traditional approach of connecting analog audio-video cabling versus the structured cabling approach in the digital signage environment, highlighting the benefits of using pre-installed unshielded twisted pair for analog audio-video.

Traditional Approach:

The traditional method of connecting digital signage equipment is achieved by connecting the client server to the display using standard coaxial AV cables such as RG6 coax, VGA cable and RCA cables.  

The problem with this approach is that due to the distance and space limitations, the cabling tends to be randomly distributed without proper organization or management.   Connections become difficult to identify and cabling often ends up being duct-taped to the floor.  Furthermore wiring costs can be prohibitive as multiple coax cables are needed for each AV channel. For example three cables are needed for each S-Video/Audio connection and three cables are needed for each Component Video (YPbPr) connection.  The distance limitations of coax cable also force the source equipment to inevitably be stacked on top or near the display equipment.

As shown below, by applying a structured cabling approach, many of these problems and limitations may be avoided.

Structured Cabling Approach

Using a structured cabling approach, the client video servers and displays are connected to each other via Category 5/5e/6 twisted pair cable.   The client video server and cable management hardware is installed in a secure telecom room.  Analog audio-video outputs from each display are converted to Cat5 cable and connected back to the telecom room as illustrated in the following diagram. 

By installing all source hardware in a remote telecom room, the entire installation can be better organized and managed.  Several Cat5 cables replace bundles of coax cables for neater and cost-efficient wiring.  AV baluns may be rackmounted at the head end and tailored to the changing needs of the installation.  

Bulky VGA is also replaced by Cat5 and by doing greater distance is achieved.  From the installer standpoint all cabling connections follow EIA568 wiring and therefore standard SCS cabling techniques are used.

In regard to systems where the same source is distributed to multiple displays, there are Cat5 distribution amplifiers that drastically reduce cabling costs.  Shown below is a typical HDTV Component Video distribution amplifier for Cat5.  Today it is possible to distribute component HDTV (1080i/p) over Cat5 without the need for any coax cable and with only passive baluns at the edge equipment.

Finally, from the end user standpoint, by having the Cat5 cabling behind the wall, a more aesthetically pleasing environment is preserved.

Guidelines

From the contractor’s perspective, when planning a digital signage installation using baluns and Cat5 twisted pair, the following tips will help save time. 

1. Check that wiring is according to EIA568A or B and straight-thru. 
2. Verify that there are no possible sources of ground loop and ensure that there is only one local ground for the entire system.
3. If a CATV source is connected, ensure that the RF cable shield is properly grounded.  It is possible that interference from an external CATV source can leak into a Cat5 AV installation.
4. When using audio-video baluns, verify that the required cabled length is within the specifications of the vendor’s balun.
5. Where possible, try to use “low-skew” video twisted pair cable.

Quick Links

The following are some useful links pertaining to audio-video and twisted pair cable.

Video and UTP: http://belden.com/pdfs/Techpprs/VideoandUTP.pdf

Skew and UTP: http://www.architechmag.com/Articles/detailArchitech.asp?ArticleID=3139

Audio-Video Glossary: http://www.kramerelectronics.com/glossary.asp?orderby=P

EIA Standards: http://www.siemon.com/us/standards/

Conclusion

In summary, regardless of the type of digital signage application, analog AV connections may be streamlined by applying a structured cabling approach.   For more information, contact your local commercial or residential AV/telecom systems integrator or cabling specialist.

Biography

MuxLab is a designer and manufacturer of security video and audio-video connectivity solutions for copper twisted pair cabling.  Jeffrey Herman is a Product Manager at MuxLab Inc (www.muxlab.com).  He may be contacted at j.herman@muxlab.com or at 514-905-0588.