Broadbandindia Magazine

Television products and services have enjoyed explosive growth in recent years. Wide-screen and flat-screen TVs are among the hottest products on the consumer market. Exciting changes to TV technology have the potential to create growth opportunities for the low voltage cabling industry. We can participate in this new wave of technology by distributing television on twisted pair cable.

Benefits of Twisted Pair Cable Relative to Coax

•  Simplicity One type of horizontal cable delivers, voice, data and television.
•  Flexibility Moves, adds and changes are as easy with TVs as they are with phones or computers.
•  Reliability The home run design inherent in twisted pair networks improves reliablity because there are no taps or splitters between the hubs and TVs. This prevents problems with loose connections that compromise picture quality on all TVs downstream from the faulty connectors.  Standards Compliance Building Automation Standard TIA/EIA 862 recognizes two cables for horizontal cabling: twisted pair cable and fiber. It does not recongize coax.
•  Bridge to IPTV Internet protocol television will probably be available for commercial applications within the next ten years, and it will probably run on twisted pair cable. Televisions that are already  connected to a twisted pair network will have a seamless transition to IPTV.

Delivering TV Signals on Twisted Pair

Three processes deliver television on twisted pair cable. One process creates a balanced signal, where voltage on each side of the twisted pair is 180 degrees out of phase from the signal on the opposite side. The second is an impedance matching capability that provides 75 ohms on the coax side of the unit and 100 ohms on the twisted pair side. The third is common mode filtration, which removes any unwanted signals that enter the unshielded cable.

This figure shows how the technology is packaged into usable products. The hubs in the background are “send units” located in wiring closets. The smaller units in the foreground are “receive units” located near a TV. A single coaxial input on the back of the hub is converted into 8 twisted pair outputs on the front. At the TV, the “receive units” convert the signal back to an unbalanced waveform, which travels to a TV on a short coax jumper cable.

This technology handles frequencies from 54 to 860 MHz. Given the 50 dB maximum output of most commercial amplifiers, the technology can deliver 60 analog channels over a distance of 330 feet (100 meters), 100 channels over 270 feet, or 134 channels over 225 feet. The capacity for HDTV channels would be exactly the same but channel capacity for standard definition digital TV would be three times higher.

If you need more channels for a long run, a signal can be delivered from one “single port converter” to another, allowing the full cable TV spectrum of 134 analog channels or 402 digital channels to be sent over 100 meters.

Designing the System

In a common cable TV application, the incoming signal is amplified at the headend and delivered to the wiring closet, where it is amplified again, sent to the hub, and distributed to the point of use on twisted pair cable.

A satellite TV application has a coax downlink from the dish to receivers, modulators and a combiner. These devices convert high frequency DBS satellite signals to lower frequency RF signals which then travel over a coax backbone to wiring closets. Then they are amplified and sent to the point of use on twisted pair cable. There are also applications where the headend combines multiple signals from cable TV, satellite, off air TV, DVD, and video cameras.

Regardless of the application, a good RF design has two important goals : First, the signal strength at each TV should be between -10dB and +15dB, and second, the slope at each TV should not exceed 11dB.

A computerized design model is available from the manufacturer to assist installers with system designs. The model calculates the signal strength at the TV, based on the high and low channel numbers, the length of the run and the signal strength entering the hub.

Television over Cat 5 or Cat 6 Cable

In a simple cable TV distribution application where Lynx is only delivering cable TV, an unbalanced coaxial signal goes from an amplifier to a Lynx hub, which converts it to balanced Cat 5 signals. In more elaborate applications a headend combines signals from multiple RF sources and sends them to an amplifier and Lynx hub located in an IDF closet.

RF baluns in the Lynx hub convert the RF to eight or sixteen balanced signals that travel on pair four of the Cat 5/6 cables. The back of the hub has one or two F connector input ports, and the front of the hub has eight or sixteen RJ45 output ports. At the point of use an RF balun housed in a wallplate F or a single port converter changes the signals back to coaxial form.