COAX CABLE

Coax Cable

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1. Coaxial Cable

Coaxial cable (or just coax cable) is a type of cable consisting of single core surrounded by a circular outer shield, with a insulating dielectric sandwiched between the two. The term coaxial comes from the inner conductor and outer shield sharing the same axis (they are concentric with one another). Coax is most commonly used to transmit high frequency signals over small (oscilloscope probes) and large distances (transatlantic phone cables).

coax cable cut away annotated
Figure 1. The make-up of a standard coaxial cable. Relative dimensions accurate for RG-6 (dimensions taken from http://www.farnell.com/datasheets/1697593.pdf).

RG-6 is one of the most common types of coaxial cable in residual homes due to it’s use with TVs.

Properties of popular coaxial cable types:

Name \(Z_C\) Conductor Diameter Insulator Diameter Shield Outer Diameter Jacket Outer Diameter Capacitance

RG-6

\(75\Omega\)[4]

1.0mm

4.57mm

5.2mm

6.6mm

68pF/m[4]

RG-58

\(50\Omega\)

5.0mm

82pF/m[3]

RG-59

\(75\Omega\)[3]

Properties of popular coaxial cable dielectrics[2]:

Name Propagation Velocity

Solid Polyethylene (PE)

0.659c

Foam Polyethylene (FE)

0.800c

Foam Polystyrene (FS)

0.910c

Air Space Polyethylene (ASP)

0.840-0.880c

Solid Teflon (ST)

0.694c

Air Space Teflon (AST)

0.850-0.900c

where \(c=3e8ms^{-1}\) is the speed of light in a vacuum.

1.1. Precision Capacitors From Coaxial Cable

Coax cable has a capacitance of approx. 1pF/10mm, as measured between the central conductor and the outer shield. Precision capacitors for prototype/lab use can be from trimmed lengths of coax. cable.

References


Authors

Geoffrey Hunter

Dude making stuff.

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