Coaxial Cables

Coaxial cable (or "coax) is the most common cable used for transmitting video signals. The name "coaxial" refers to the common axis of the two conductors.

Construction


A coaxial cable has a solid copper or copper-clad-steel centre conductor surrounded by a non-conductive dielectric insulating material. The dielectric is surrounded by foil shield/s and/or copper braid/s which form the outer conductor and also shield against electromagnetic interference (EMI). The outer conductor/shield is encased in a PVC jacket.

Most coaxial cables for video applications have a nominal impedance of 75 ohms. Their differing electrical and physical characteristics make it important to select the correct type of cable to suit the application. 

Types of coax
The three most commonly used coaxial cable types for video applications are RG59/U, RG6/U and RG11/U. The "RG" number originated from the "registration number" allocated by the US military to each type of cable. The "/U" indicates that the dielectric is unbounded to the centre conductor.

·         RG59/U is available with either solid copper or copper-clad-steel centre conductor. It's suitable for basic analog TV antenna feeds in residential applications and for basic CCTV systems over short cable runs. The copper-clad-steel type has high tensile strength and should be used when terminating the cable with F-Type connectors.

·         RG6/U Quad-shield is the minimum requirement under the latest Standard for digital TV antenna cabling and for all TV antennas cabling for apartments/units (MATV). It is also used for the distribution of Cable TV (CATV) and Satellite TV (SATV) in residential or commercial premises. It features a copper-clad-steel inner conductor. Single-shield, dual-shield and tri-shield versions of RG6/U are available but do not provide adequate EMI shielding.

·         RG11/U Quad-shield is used for the same applications as RG6/U for either backbone cabling or for long distribution runs. It features a copper-clad-steel inner conductor.

Choosing the correct cable
Use the table below to determine which cable should be used for your application.

Analog TV  
RG59/U   Acceptable performance on cable runs <225 meters
RG6/U     Gives superior performance on cable runs <225 meters. Used for cable runs >225 meters but <545 meters.
RG11/U   For cable runs greater than 545 meters.

CCTV
RG59/U   Acceptable performance on cable runs <225 metres
RG6/U     Gives for superior performance on cable runs <225 meters. Used for cable runs >225 meters but <545 meters.
RG11/U   For cable runs greater than 545 meters.

DTV, CATV, SATV, MATV
RG6/U     Standard cable for these applications
RG11/U   Recommended for long cable runs and for backbone cabling.

( this document is for reference only )