What is COAXIAL CABLE? What does COAXIAL CABLE mean? COAXIAL CABLE meaning & explanation


coaxial cable or coax is a type of cable

that has an inner conductor surrounded

by a tubular insulating layer surrounded

by a tubular conducting shield many

coaxial cables also have an insulating

outer sheath or jacket the term coaxial

comes from the inner conductor and the

outer shield sharing a geometric axis

coaxial cable was invented by English

engineer and mathematician Oliver

Heaviside who patented the design in

1880 coaxial cable differs from other

shielded cable used for carrying lower

frequency signals in that the dimensions

of the cable are controlled to give a

precise constant conductor spacing which

is needed for it to function efficiently

as a transmission line coaxial cable is

used as a transmission line for radio

frequency signals it's applications

include feed lines connecting radio

transmitters and receivers with their

antennas computer network internet

connections digital audio f / diff and

distributing cable television signals

one advantage of coaxial over other

types of radio transmission line is that

in an ideal coaxial cable the

electromagnetic field carrying the

signal exists only in the space between

the inner and outer conductors 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 coaxial cable also provides

protection of the signal from external

electromagnetic interference coaxial

cable conducts electrical signal using

an inner conductor usually a solid

copper stranded copper or copper plated

steel wire surrounded by an insulating

layer and all enclosed by a shield

typically one to four layers of woven

metallic braided metallic tape the cable

is protected

an outer insulating jacket normally the

shield is kept at ground potential and a

signal carrying voltage is applied to

the center conductor the advantage of

coaxial design is that electric and

magnetic fields are restricted to the

dielectric which little leakage outside

the shield

conversely electric and magnetic fields

outside the cable are largely kept from

interfering with signals inside the

cable larger diameter cables and cables

with multiple shield have less leakage

this property makes coaxial cable a good

choice for carrying weak signals that

cannot tolerate interference from the

environment or for stronger electrical

signals that must not be allowed to

radiate or couple into adjacent

structures or circuits common

applications of coaxial cable include

video and Katz distribution RF and

microwave transmission and computer and

instrumentation data connections the

characteristic impedance of the cable is

determined by the dielectric constant of

the inner insulator and variety of the

inner and outer conductors a control

cable characteristic impedance is

important because the source and load

impedance should be met to ensure

maximum power transfer and minimum

standing wave ratio other important

properties of coaxial cable include

attenuation as a function of frequency

voltage handling capability and shield

quality coaxial cable design choices at

physical size frequency performance

attenuation power handling capabilities

flexibility strength and cost the inner

conductor might be solid or stranded

stranded is more flexible to get better

high frequency performance the inner

conductor may be silver-plated copper

plated steel wire is often used as an

inner conductor for cable used in the

cable TV industry the insulator

surrounding the inner conductor may be

solid plastic a foam plastic or air with

spacers supporting the inner wire the

properties of dielectric control some

electrical properties of the cable a

common choice is a solid polyethylene

the insulator used in lower loss cables

solid Heflin PTFE is also used as an

insulator some coaxial lines use air or

some other gas and if spaces to keep the

inner conductor from touching the shield

many conventional coaxial cables use

braided copper wire forming the shield

this allows the cable to be flexible but

it also means there are gaps in the

shield layer and the inner dimension of

the shield varies slightly because the

brain cannot be flat sometimes the braid

is silver-plated for better shield

performance some cables have a double

layer shield the shield might be just

two brains but it is more common now to

have a thin foil shield covered by a

wire braid some cables may invest in

more than two shield layers such as quad

shield which uses for alternating layers

of foil and braid other shield design

sacrifice flexibility for better

performance some shields are a solid

metal tube those cables cannot be been

sharply as the shield will king causing

losses in the cable for high power radio

frequency transmission up to about one

gigahertz coaxial cable with a solid

copper outer conductor is available in

sizes of 0.25 inch upward the outer

conductor is rippled like a bellows to

permit flexibility and the inner

conductor is held in position by a

plastic spiral to approximate an aired

electric coaxial cables require an

internal structure of an insulating

dielectric material to maintain the

spacing between the center conductor and

shield the electric losses increase in

this order ideal dielectric no loss

vacuum air polytetrafluoroethylene PTFE

polyethylene foam and solid polyethylene

a low relative permittivity allows for

higher frequency usage and in

homogeneous electric needs to be

compensated by a non-circular conductor

to avoid current hotspots

while many cables have a solid electric

many others have a foamed electric that

contains as

taras or gas is possible to reduce the

losses by allowing the use of a larger

diameter center conductor foam cooks

will have about 15 percent less

attenuation but some types of foamed

electric can absorb moisture especially

at its many surfaces in humid

environments significantly increasing

the loss support shaped like stars or

spokes are even better but more

expensive and very susceptible to

moisture infiltration still more

expensive were the airspace coaxials

used for some intercity communications

in the mid twentieth century the center

conductor was suspended by polyethylene

discs every few centimetres in some low

loss coaxial cables such as the RG 62

type the inner conductor is supported by

a spiral strand of polyethylene so that

an air space exists between most of the

conductor and the inside of the jacket

the lower dielectric constant of air

allows for a greater inner diameter at

the same impedance and a greater outer

diameter at the same cutoff frequency

lowering ohmic losses inner conductors

are sometimes silver-plated to smooth

the surface and reduce losses due to

skin effect a rough surface prolongs the

path for the current and concentrates

the current at peaks and vas increases

ohmic losses the insulating jacket can

be made from many materials a common

choice is PVC but some applications may

require fire resistant materials outdoor

applications may require the jacket

resistant or violet light oxidation

rodent damage or direct burial flooded

coaxial cables use a water blocking gel

to protect the cable from water

infiltration through minor cuts in the

jacket for internal chassis connections

the insulating jacket may be omitted