Coaxial cable is an electrical cable consisting of a round, insulated conducting wire surrounded by a round, conducting sheath, usually surrounded by a final insulating layer. It is designed to carry a high-frequency or broadband signal, usually at radio frequencies.

Coaxial Cabling is a two conductor, unbalanced, closed transmission medium that is used for the transmission of RF energy. It yields excellent performance at high frequencies and superior EMI control/shielding when compared to other types of copper cabling.

Listed below are some common terms and definitions that are related to coaxial cabling


Attenuation (Insertion Loss)

Loss of power. Attenuation is usually measured in dB loss per length of cable (ex. 31.0 dB/100Ft.). Attenuation increases as frequency increases.

BALUN

An acronym for BALanced/UNbalanced. A device commonly used to change one cabling media to another (ex. coaxial to Ladder Line balun).

Center Conductor

The solid or stranded wire in the middle of the coaxial cable. The conductor diameter is measured by the American Wire Gauge (AWG).

Coaxial Adaptor

A device used to change one connector type to another or one gender to another (ex. BNC to SMA Adaptor).

Coaxial Cable

A two conductor cylindrical transmission line typically comprised of a center conductor, an insulating dielectric material and an outer conductor (shielding). Coaxial cable can be flexible, semi-rigid or rigid.

Coaxial Connector

The interconnection device found at each end of a coaxial cable assembly. There are many common types of coaxial connectors such as: BNC, SMA, SMB, F, PL259, N.

Dielectric

The insulating material that separates the center conductor and the shielding.

Electromagnetic Interference (EMI)

Electrical or electro-magnetic energy that disrupts electrical signals.

Frequency

The number of times a periodic action occurs in one second. Measured in Hertz.

Impedance

The opposition to the flow of alternating or varying current. Measured in Ohms.

Jack

The female connector usually containing a center socket.

Plug

The male connector usually containing a center pin.

RG/U

Symbols used to represent coaxial cable that is built to U.S. government specifications (R=Radio Frequency, G=Government, U=Universal Specification).

Shielding

Conductive envelope made of wires or metal foil that covers the dielectric and the center conductor.

(V)SWR ((Voltage) Standing Wave Ratio)

Amount of reflected power expressed as a ratio (Ex. 1.25:1) VSWR increases as frequency increases.


STANDARD CABLE TYPES

Most coaxial cables have a characteristic impedance of either 50 or 75 ohms. The RF industry uses standard type-names for coaxial cables. The U.S military uses the RG-# or RG-#/U format


The common RG-58 from your local emporium is NOT the best you can do and will lower your output power by the time it reaches the antenna, so use it only for short runs.


So where does all this lost power go? Its dissipated as heat inside the cable. With a 100W transmitter you'll already notice your RG58 heating up after several minutes of transmission which is definitely not what you want.

Watch out for the correct impedance:- RG-8 and RG-58 have 50 Ohm impedance, whilst RG-59 and RG-6 (Low Loss Version of RG-59) have 75 Ohm impedance. Many antennas are 50 ohm impedance and so are most transmitters.


Don't fit more than you need to make the long run to your antenna as coiling can alter the SWR and possibly be a trip hazard. Also don't make up a few "patch cables" to go between your radio, VSWR meter and your antenna as all you'll do is create higher SWR and more line losses. Finally, don't use cheap TV cable (I have seen it done!).


All above courtesy of Brian Perrett and Highfield Amateur Radio Club


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Coaxial Cable

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