The coaxial cable (coax) is typically identified or classified according to its impedance or RG-type, for example, a 50-ohm coax or an RG-8 type.
A coaxial cable consists of two conductors separated by a dielectric material. The centre conductor and the outer conductor or shield are configured in such a way that they form concentric cylinders with a common axis (hence co-axial).
The centre conductor may be made of various materials and constructions. Most common constructions are solid or seven-strand conductors. Solid conductors are used in permanent, infrequently handled or low flex applications and stranded conductors used in flexible cable applications.
Common materials include copper, tinned or silver plated copper, copper clad steel and copper clad aluminium.
Plated copper is used to aid in solderability of connectors or to minimise corrosion effects. Because of a phenomenon known as skin-effect, copper clad materials may be used in higher frequency applications.
Insulation or dielectric materials are used to provide separation between the conductors. It is desirable that the material has stable electrical characteristics (dielectric constant and dissipation factor) across a broad frequency range.
Common materials used are polyethylene (PE), polypropylene (PP), fluorinated ethylene propylene (FEP) and polytetrafluoroethylene (PTFE).
The outer conductor is typically made from a number of smaller aluminium or copper conductors combined together. These conductors are woven together to form a braid around the dielectric core. For higher frequency applications, a second braid or aluminium foil tapes are often added to improve attenuation and shield effectiveness.
The jacket material serves as a protective covering from the environment and may also serve to add in the overall flame retardant properties of the cable. Typical materials include polyvinyl chloride (PVC), PE, FEP and polyvinylidene fluoride (PVDF).
Belden’s Coaxial cables are tested with equipment that simulates every known environmental and electrical performance condition. As a result, these cables can be counted on for positive, reliable and trouble-free operation.
The coaxial cables are engineered in a wide selection of sizes and materials, with each offering the benefits needed for physical, electrical and cost-requirement applications. Cable choices include broadband, standard analogue, precision video for analogue and digital, bundled RGB, high-flex SVHS, video triax, conformable coax and more.
The cable's shielding is an important aspect in the cable's design.
Wide range of shielding options are available, such as the following:
Duofoil
Duofoil is a shield in which metallic foil is applied to both sides of a supporting polyester or polypropylene film.
Duobond
Duobond is essentially the same construction as Duofoil (a laminated shielding tape consisting of aluminium foil/plastic film/aluminium foil) but with an extra layer of heat-sensitive adhesive bonding the foil shield to the dielectric core. This foil shield provides 100% coverage and ensures maximum shield protection.
Duobond II (Foil/Braid)
Duobond II combines all the features of Duobond with an outer braid applied for better protection against interference and to increase the overall tensile strength.
Duobond III (Tri-Shield)
Duobond III utilises the Duobond II design (foil/braid) plus an additional surrounding layer of Duofoil. This extra layer of foil improves shield reliability and provides an additional interference barrier.
Duobond IV (Quad Shield)
Duobond IV adds a second layer of braid to the Tri-shield design (foil/braid/foil/braid). This extra layer of braid shield provides improved strength and durability.
Duobond Plus
This shield features the same foil/braid/foil construction as Duobond II but with the additional of a shorting fold in the outermost foil. This fold prevents a slot opening from being created in the shield, thereby preventing signal egress or ingress.
This unique feature creates the effect of a solid metal conduit, which improves the high-frequency performance of the cable.