Coax Cable

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).

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$1	1.0mm	4.57mm	5.2mm	6.6mm	68pF/m 1
RG-58	$50\Omega$	5.0mm	82pF/m2
RG-59	$75\Omega$2

Properties of popular coaxial cable dielectrics³:

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.

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

Footnotes

1. Wikipedia (2021, Sep 7). RG-6. Retrieved 2022-01-31, from https://en.wikipedia.org/wiki/RG-6. ↩ ↩²

2. Wikipedia (2020, Dec 19). RG-58. Retrieved 2022-01-31, from https://en.wikipedia.org/wiki/RG-58. ↩ ↩²

3. RF Cafe. Coaxial Cable Specifications. Retrieved 2021-05-05, from https://www.rfcafe.com/references/electrical/coax-chart.htm. ↩