Broadband video, Internet Protocol Television, and other entertainment applications can run on high-performance twisted-pair cabling.
Broadband video refers to a class of applications that transmit a wide range of radio frequencies (RF)—typically, up to 900 MHz—or channels, over 75-O coaxial cabling. Examples of broadband video services are:
- Cable television, also known as antenna broadcasting or CATV;
- Satellite video signals, whose transmission frequency is the microwave range and that are quadrature-amplitude-modulation (QAM) modulated and converted into digital cable format;
- Off-air or in-house video transmissions in analog or digital cable format;
- Playback devices, such as DVDs and VCRs, whose output signal have been modulated into analog or digital cable format.
A structured cabling approach for broadband video distribution improves reliability because there are no taps or splitters between the video-distribution hub and the television or monitor.
Broadband video applications are optimally suited for transmission over twisted-pair cabling and require a pair of video baluns for conversion of the coaxial input signal. The video baluns convert balanced twisted-pair signals to 75-O broadband video signals using common video interfaces, such as Type F and phase alternating line (PAL) connectors. Amazingly, both analog and digital video and audio—including 480 i/p standard-definition television (SDTV) and 720p and 1080 i/p high-definition television (HDTV)—can be transmitted over one pair (the 7/8 pair) of a twisted-pair cable. Broadband video applications also represent and excellent opportunity to take advantage of the cable-sharing capability of Category 7/7A fully shielded solutions.
Category and quality
A wide range of structured cabling supports broadband video applications. While broadband video is acceptable for operation over Category 5e cabling, experimental results originally published by NORDX (now part of Belden) in 2003 demonstrate that cabling with lower insertion loss and higher signal-to-noise margins, such as Category 6 and higher, deliver improved picture quality when signal levels are weak.
With broadband video applications, no external powering is required for the passive balun devices. Baluns permit bidirectional operation for such features as video-on-demand, and are extremely reliable. As with coaxial distribution systems, however, signal amplification may be required depending upon the incoming signal strength, length of each run, and the highest and lowest channel being distributed. (See sidebar, above.)
Amplification is usually provided before the video-distribution hub, and one amplifier can serve up to 24 drops in each telecommunications room (TR). You should refer to signal charts provided by the balun manufacturer for detailed design guidance.
In a typical implementation topology for a structured cabling solution supporting multiple broadband video applications, as seen in the opening figure, broadband video feeds from multiple sources may be merged with a combiner. A splitter is used to distribute the incoming broadband video source to the work areas; note that 75-O port terminators should be applied to all unused splitter ports to prevent electromagnetic emissions.
A structured cabling approach for broadband video distribution improves reliability because there are no taps or splitters between the video-distribution hub and the television or monitor. In addition, because each viewing device is serviced by a dedicated cable, the signal strength on existing drops is not affected when new televisions and/or monitors are added to the system.
If there are multiple video-distribution hubs, one hub should be used to support the shortest runs, another hub to support mid-length runs, and a third hub be used to support the long runs. This will maximize the use of signal amplifiers because short runs require little or not amplification, mid-length runs require moderate amplification, and long runs require significant amplification. Grouping runs of similar lengths ensures that optimal strength and quality are delivered to each television or monitor. As with all broadband video solutions, emissions testing is recommended after the installation is complete.
The intelligent advantage of IP-based technology may soon be capturing a share of the CATV market in the form of IPTV. In this high-definition video application, IPTV signals are transmitted via IP packets, and a set-top box at the customer location decodes the packets and sends the image to the television. IPTV offers viewers an on-demand experience and limited (for now) Internet-access capability to sites providing such information as local weather forecasts, personalized stock quotes, and streaming videos.
IPTV is a secure, closed system with content that is managed by a service provider, or by an end-user that centrally manages in-house IPTV equipment and delivers content to specific on- and off-site locations. Because of the flexibility to manage content, IPTV is a growing trend in the hospitality and hospital industry, as well as in the residential community.
According to Kurt Scherf, vice president and principal analyst for Parks Associates (www.parksassociates.com), In terms of the percentage growth in IPTV, the U.S. is actually near the top of the market. There were only 300,000 subscribers at the end of 2006, and now there are 1.2 million, which is significant growth.
IPTV operates over a range of data cabling, as shown in the table Structured cabling for video applications. Today's challenges associated with IPTV include:
- Maximizing the video-compression format to ensure that bandwidth requirements are not exceeded (bandwidth needs to increase as the number of televisions in a single facility increases);
- Picture quality is not disrupted (e.g., no small digitized squares appear on the screen, due to congestion and errors on the service line);
- Delays associated with changing channels (i.e., channel zapping) are minimized.
IPTV performance will improve significantly once infrastructures become capable of supporting faster Ethernet speeds—1000Base-T and 10GBase-T capability is expected to eliminate all bottlenecks while supporting superior content transmission—and migration to these faster transmission rates takes place.
While this article focuses on the most common video applications traditionally supported by coaxial cabling, keep in mind that balanced twisted-pair cabling is capable of supporting many other video formats, such as High Definition Multimedia Interface (HDMI), Video Graphic Array (VGA), Super Video Home System (SVHS), and composite/component video with the use of appropriate baluns.
Simple channel deployment of these applications may require the use of up to all four twisted pairs and, in the case of HDMI, may even require two 4-pair cables. More advanced video distribution methods, such as using a modulator to convert the input signal to a cable signal at the headend, may support reduced pair counts, as well as cable-sharing implementations.
In all cases, using balanced twisted-pair cabling to support video applications offers multiple advantages over a coaxial cabling system including convergence of applications over one common infrastructure and full support of standards-based cabling distances and topologies.
VALERIE MAGUIRE is global sales engineer with Siemon (www.siemon.com). This is the conclusion of an article whose first part was published last month. (See Using your infrastructure to support video applications, January 2009)
Video amplification techniques
In some broadband video applications, signal amplification may be required depending on the incoming signal strength, length of each run, and the highest and lowest channel being distributed. It is generally accepted that video signals must fall in the range of -10 dBmV* to +15 dBmV to be properly displayed by televisions and monitors.
An RF signal-strength meter is used to collect these measurements. Note that bidirectional amplifiers are required to support digital broadband video applications to ensure that sufficient signal strength is delivered on the return path to the service provider.
Video amplifiers are available for as little as $10. More expensive amplifiers offer greater gain, more features, cleaner signal output, cooler operation, and longer life. Optional amplifier tilt and gain adjustments can be beneficial in ensuring that one end of the video signal spectrum (e.g., the low-frequency range) is not overamplified when signals at the opposite end of the spectrum (e.g., the high range) are boosted.
The level of amplification required can be predicted by referencing signal attenuation charts provided by the broadband video balun or structured cabling manufacturer. These charts are developed by comparing the approximate signal loss associated with the cabling, video baluns, video-distribution hub, and splitters to the incoming signal level. Cabling with improved insertion loss and signal-to-noise margin will support broadband video applications over the longest distances with the least amount of signal amplification. The table above shows typical distances supported at various frequencies by the TERA brand Category 7A fully shielded cabling solution and two video baluns with signal amplification. The use of video receiving equipment with higher input sensitivity (e.g., 10 dBmV) may result in longer-distance support. —V.M.
* A power measurement of x dBmV indicates that a particular signal is x dB greater than 1 mV in a 75-O coaxial cabling system. A negative dBmV value indicates that a signal is x dB less than 1 mV. The following equation is used to convert x mV to dBmV: dBmV = 20 log (x mV). Using this formula, 0 dBmV is equal to 1 mV in a 75-O coaxial cabling system.