Coaxial cable

Coaxial cable is a type of transmission line, used to carry high-frequency electrical signals with low losses.

This allows coaxial cable runs to be installed next to metal objects such as gutters without the power losses that occur in other types of transmission lines.

Common applications of coaxial cable include video and CATV distribution, RF and microwave transmission, and computer and instrumentation data connections.

Other important properties of coaxial cable include attenuation as a function of frequency, voltage handling capability, and shield quality.

[3] Coaxial cable design choices affect physical size, frequency performance, attenuation, power handling capabilities, flexibility, strength, and cost.

[examples needed] For high-power radio-frequency transmission up to about 1 GHz, coaxial cable with a solid copper outer conductor is available in sizes of 0.25 inch upward.

[6] Coaxial cables require an internal structure of an insulating (dielectric) material to maintain the spacing between the center conductor and shield.

Outdoor applications may require the jacket to resist ultraviolet light, oxidation, rodent damage, or direct burial.

They cannot be bent, tightly twisted, or otherwise shaped without changing their characteristic impedance, causing reflection of the signal back toward the source.

They also cannot be buried or run along or attached to anything conductive, as the extended fields will induce currents in the nearby conductors causing unwanted radiation and detuning of the line.

Coaxial lines largely solve this problem by confining virtually all of the electromagnetic wave to the area inside the cable.

It is usually undesirable to transmit signals above the cutoff frequency, since it may cause multiple modes with different phase velocities to propagate, interfering with each other.

A propagating surface-wave mode that only involves the central conductor also exists, but is effectively suppressed in coaxial cable of conventional geometry and common impedance.

Due to the skin effect, the RF signal is only carried by the plating at higher frequencies and does not penetrate to the connector body.

These typically involve such low levels of RF power that power-handling and high-voltage breakdown characteristics are unimportant when compared to attenuation.

They introduce standing waves, which increase losses and can even result in cable dielectric breakdown with high-power transmission.

The magnitude of an alternating current in a conductor decays exponentially with distance beneath the surface, with the depth of penetration being proportional to the square root of the resistivity.

[17] A continuous current, even if small, along the imperfect shield of a coaxial cable can cause visible or audible interference.

However, ladder line is extremely sensitive to surrounding metal objects, which can enter the fields before they completely cancel.

This effect was manifested when trying to send a plain voice signal across the transatlantic telegraph cable, with poor results.

However, the RG-series designations were so common for generations that they are still used, although critical users should be aware that since the handbook is withdrawn there is no standard to guarantee the electrical and physical characteristics of a cable described as "RG-# type".

The RG designators are mostly used to identify compatible connectors that fit the inner conductor, dielectric, and jacket dimensions of the old RG-series cables.

[42] There are also other designation schemes for coaxial cables such as the URM, CT, BT, RA, PSF and WF series.

Short coaxial cables are commonly used to connect home video equipment, in ham radio setups, and in Nuclear Instrumentation Modules.

Smaller varieties of hard line may be used internally in some high-frequency applications, in particular in equipment within the microwave range, to reduce interference between stages of the device.

"Plenum" cabling is expensive and comes with a special Teflon-based outer jacket designed for use in ventilation ducts to meet fire codes.

It was developed since the plastics used as the outer jacket and inner insulation in many "Plain" or "house" cabling gives off poisonous gas when burned.

This type of coax offers superior screening compared to cables with a braided outer conductor, especially at higher frequencies.

In the interests of saving weight and costs, on masts and similar structures the outer line is often aluminium, and special care must be taken to prevent corrosion.

"Quad-shield" cable, using two low-coverage aluminum braid shields and two layers of foil, is often used in situations involving troublesome interference, but is less effective than a single layer of foil and single high-coverage copper braid shield such as is found on broadcast-quality precision video cable.