Coaxial Cable Basics
What is a coaxial cable?
Coaxial cables, sometimes called coax cables, are electrical cables that carry radio frequency (RF) signals from one end to the other. These high-frequency cables are two-pole cables with concentric construction and are used where high-frequency signals must be transmitted. They are used in antenna, transmission and measurement technology. The technology has been in use since the beginning of the 20th century. Thanks to their durability and ease of installation, these cables are mainly used to connect satellite antenna systems in homes and businesses to television sets. In the professional sector, they are used for broadcasting and radar systems. Therefore, they are also called antenna cables or satellite cables. Coaxial cables are simple in design and popular because the center conductor is always shielded. This allows it to transmit data quickly while protecting it from damage and interference.
How are coaxial cables constructed?
There are several types of coaxial cables, which differ in dimension and impedance (AC resistance). The dimension refers to the cable thickness and is described by the RG number. The larger the RG number, the thinner the central conductor core. Since all coaxial cables have an insulating layer, they have a larger diameter than normal cables. Coaxial cables are mainly composed of the following four layers:
- Inner conductor The inner conductor, also called the core, is usually a rigid copper wire. Depending on the design of the coaxial cable, the inner conductor has different diameters. The flexible version of coaxial cables then have inner conductors made of thin, braided copper wires
- Dielectric The dielectric is an insulation layer that separates the inner conductor from the outer shield. The insulation is usually made of plastic such as polyethylene and gives the cable its characteristic stiffness. The dielectric is largely responsible for the line characteristic impedance and attenuation.
- Shielding The shield is a metallic sheath that protects the inner conductor from electromagnetic influences. It usually consists of a flexible braid or also of a wound metal foil. The shielding is a decisive factor for the transmission reliability of a coaxial cable .In practice, a combination of braided shield and aluminum foil is often found. The electric field that builds up when a voltage is applied occurs only between the outer and inner conductors. No magnetic field occurs outside the cable.
- Cable sheath The cable sheath is the outer protection of a cable. It protects the inside of the cable against moisture, mechanical and chemical stress and solar radiation. An elastic plastic is usually used for the sheath.
How do coaxial cables work?
Coaxial cables transmit signals in the inner conductor, while the surrounding shielding minimizes any signal loss through attenuation and blocks electromagnetic interference from foreign fields and other radio transmissions. The dielectric, or layer between the inner conductor and the outer layers, creates spacing and thus provides insulation. Advantages of coaxial cables Coaxial cables are very inexpensive because they have a simple structure and are used worldwide in large quantities. They are easy to wire and install and just as easy to extend. Coaxial cables are suitable for data transmissions up to 10 Mbps. In addition, they are considered durable and at the same time future-proof. Another advantage of coaxial cables is that the electromagnetic field that transmits the signal exists only in the area between the inner and outer conductors and does not penetrate to the outside. Unlike other transmission paths, coaxial cables are thus less susceptible to electromagnetic interference and can be installed next to metallic wires and surfaces without degrading their performance.
Coaxial cable and antenna cable connectors
Coaxial connectors have been developed to realize detachable connections of coaxial cables. The structure of the connectors corresponds to the layering in the coaxial cable. The inner conductor is always protected by good shielding from electromagnetic influences, even in the connector. Coaxial cable connectors maintain the shielding of the cable when a plug connection is made. There are two different connection types: Male and Female. Plugs have metal pins that protrude from the center, and sockets have a countersunk hole to accept the pin. Different types of connectors can be fitted to coaxial cables, depending on the application.
The main coaxial connectors are:
- RCA connector
- BNC connector
- IEC connector
- F connector
- MCX, MMCX, SSMCX
- PL connector
- N connector
- SMA/SMA-reverse, SMB
- SMC connector
- FME connector
There are also useful adapters for coax connections. A splitter (also called antenna splitter) makes it possible to send a signal in parallel to two end devices with coax connection. If you want to make a long coax cable out of several short ones, an appropriate adapter for the extension will help you. Pay attention to whether you want to connect sockets or plugs. You will need a 90-degree angle adapter if the stiff coaxial cable has to make a sharp bend behind cabinets or around door frames.