Video triaxial cables

Triax cables

The TRIAX system exploits a triple co-axial construction. Instead of one shield the cable features two concentric shields. Trinax cables are like coaxial cables where the one center conductor is surrounded with two shield layers insulated from each other. You can think a triaxial (or short triax) cable as being a full coaxial cable surrounde by an extra metallic shield layer and outer insulator.

Typical triax cable is like a very low loss coaxial cable with very good shielding properties. Triax cables are generally used in some instumentation and RF applications where special shielding is needed. Triax cable is ideal for high cross-talk environments such as antenna-, radar-, and broadcast systems. Triaxial connectors and cable assemblies are used where very low- and high level RF signals are transmitted simultaneously through cables which are bundled or located in high energy fields caused by radar or transmitters.

In instrumentation aplications the outer shield is usually used as the earth, while the inner shield is usually fed by its own driver amplifier.

Triax cables are used in TV broadcast industry for TV camera interconnections (connecting camera to CCU and supplying power to camera). Triaxial cables are constructed with a solid or stranded center conductor and two isolated shields. The center conductor and the inner isolated shield make up a coaxial cable configuration that functions to carry the video signal. The outer isolated shield can be used for several separate signals by means of multiplexing that may include power feed, teleprompter feeds and control for automation. Triax Cable is designed with two isolated shields to provide multiple functions through one cable to your camera such as power. There are two versions of triax cable commonly used in TV industry: RG59 (3/8") and RG11 (1/2"). Typical triax camera system can send the picture from over a triax cable for up to 500 meters with no degradation. Camera set-ups that can be remotely adjusted though ta cable, as well as usually intercom functions. There are (at least have been) two types of triax systems in use in broadcast industry: analogue triax and digital triax. In conventional Analog Triax the signals (component video, audio, intercom, control etc.) are modulated onto different frequency FM carriers which are carried through the same cable. Digital Triax is Component Digital video (plus other signals) running down the cable.

Triaxial cables are primarily used for electrical connections for video cameras and transmission systems. Their high-quality materials and high-precision balanced design maximise their transmission properties (low attenuation, even characteristic impedance). The smooth outer braided screen enables cameras to be supplied with power.

Triaxial cables are used in TV broadcast industry for TV camera interconnections (connecting camera to CCU and supplying power to camera). Triax is a clever (though complex and expensive) system to enable a broadcast television camera to 'communicate' with its base station by means of a single fairly light weight co-axial cable. Triax is a cable used primarily in analog video camera applications. It contains a coax, inner jacket, braid, and overall jacket. The coax is used to transmit the video signal. The two braids are used to send power and multiplex various other signals from the CCU to the camera.

Triaxial cables are constructed with a solid or stranded center conductor and two isolated shields. Triaxial cables which are essentially coaxial cables with an added outer shield that lowers ground loop interference and eliminates radiated noise or cross-talk. Various triax cables are available in RG-59/U RG-6/U and RG-11/U 75 ohm constructions. The standard sizes include RG59/U and RG11/U types. The RG59/U is the smaller of the two and is generally more flexible. RG11/U has lower attenuation values that will allow longer cable runs. The metric size triaxial is similar, being the smaller size is generally more flexible and the larger size having lower attenuation values.

The center conductor and the inner isolated shield make up a coaxial cable configuration that functions to carry the video signal. The outer isolated shield can be used for several separate signals by means of multiplexing that may include power feed, teleprompter feeds and control for automation.

Triax Cable is designed with two isolated shields to provide multiple functions through one cable to your camera such as power. There are two versions of triax cable commonly used in TV industry: RG59 (3/8") and RG11 (1/2"). In Triax applications the cable types used are generally referred with their thickness: 14 mm, 11 mm and 8 mm Triax cable. Triax cables use special tiax connectors. The TV industry generally uses the connectors made by Lemo and Fischer. There are at least three different commonly used triax connectors in TV production industry. Typical triax camera system can send the picture from over a triax cable for up to 500 meters with no degradation. Camera set-ups that can be remotely adjusted though ta cable, as well as usually intercom functions.

There are (at least have been) two types of triax systems in use in broadcast industry: analogue triax and digital triax. In conventional Analog Triax the signals (component video, audio, intercom, control etc.) are modulated onto different frequency carriers which are carried through the same cable. The audio, video and control signals are then modulated to those carriers using suitable modulation (for example FM modulation). Typically the various video and audio signals from the camera are modulated into various FM radio carriers, and sent down the centre conductor. At the same time RF modulated communication, video feeds and control instructions were travelling in opposite direction back to the camera. The triax adapter sorted all of this out. The camera had power, syncronising and control signals, the cameraman had video feeds and two way communication, and the director had 'perfect' video and audio signals. For example Triax-HD used by Philips uses Y/Cr/Cb transmitted as 30/15/15 MHz frequencies.

In Digital Triax system Component Digital video (plus other signals) running down the cable in digital from (data rates up to around around 300 Mbit/s).

Triax cable is not used in home video systems. Triax cable is extensively used in professional video broadcasting industry. Triax cabling is typically installed to many places where large events (concents, sports events etc.) take place for the video system to easily allow for professional broadcast applications.

In a typical triax system there are the following parts:

• Video camera
• Camera Adapter Unit (CAU): Adapter box on the camera end that connects triax cable to camera. This adapter receives signals from triax and connect those to camera.
• Camera Control Unit (CCU): This is the unit on the video control room where the triax cable. It sends camera power to triax cable and adapts all the signals on triax cable to suitable signals that can be connected to rest of video production system. All camera control functions are available from the control panel located at the CCU.
• Triax cable: The cable between CCU and CAU

When using triax cable, the overall system is powered by AC power at the CCU. Because the cable length can be very long (up to hundreds of meters) and considerable power needs to be transported (large camera and local monitor), the voltages transported through the triax cable can be quite high (up to 160V DC or 250V AC on some systems) to allow long distance power transfer (resistance can be 5-30 ohms per kilometer). The high supply voltage is converted in the camera adapter to 12V DC by a switched mode power supply. Because of high voltages on the cable, there are various special precautions that are taken in account to monitor earth leakage etc. to prevent electric shock under fault (damaged cable) conditions.

Do not connect or disconnect the triax cable with the system powered up. Avoid the possibility that anyone can get into contact with the signals on the cable. For professional video use, it is recommended that the used triax cable is made of pure copper. The DC resistance of copper-coated steel triax cable is much higher and maximum cable length may be limited to one-third or less of rated length due to power losses in the cable.

A typical triax system has the bi-directional signal multiplexing capability that provides power, genlock, return video, program audio, intercom, tally and complete camera control from the CCU to the CAU.

Adaptation to use coax cable: The same multiplexing idea as used in triax can be used also with coax cable. In coax adaptations, the same signals are carried through 75 ohm coaxial cable but the cameras are locally powered from some other source than through the cable.