A coaxial cable is a cable that has a center conductor and a shield that are aligned and separated by a void that can be filled with insulating material. This type of cable is used to transmit RF signals. It differs from ordinary wire (which is used to transmit direct current) in a more uniform cross-section and the use of expensive (and higher quality) materials both for the conductor itself and for insulation.
Coaxial Cable Components
A typical coaxial cable consists of four components:
- Conductor, which can be either a single and straight wire, or stranded. It can also be a tube made of various alloys: copper, aluminum, steel, silver-plated, and other options. Accordingly, different types of conductors have different characteristics and are used for different purposes.
- Insulation can be either semi-air or solid. Various materials can be used for insulation, it largely depends on the properties of the conductor and operating conditions. The main goal is to ensure the alignment of two conductors and dielectric properties.
- Outer Conductor (which can also be called a “screen”). It can be in various forms: foil, braid, film that is coated with aluminum, tapes made of aluminum or copper alloys, and other options.
Application and Use
List of main areas of application
- Antenna systems;
- Signaling and automation systems;
- Broadcasting systems and networks;
- In communication systems;
- Automated control systems;
- Video surveillance systems;
- Military equipment.
Classification of coaxial cables
There are relatively few classification factors for coaxial cables. Apart from the classification by purpose, only a few can be distinguished as the main characteristics.
- Solid tinned braid;
- Solid metal tube;
- Plain with a standard single-layer braid;
- Conventional with multi-layer braiding, in this case, additional layers can often be used.
Separately, it is worth highlighting radiating coaxial cables, which have a very low degree of shielding. In addition, often it can also be controlled.
By wave impedance
If we talk about international standards, then there are only three types (the highest has a value of 100 ohms). At the same time, only the first two standards are used frequently, the rest are used very rarely and for special purposes. That is, they are practically never encountered in everyday life.
- 50 Ohm – refers to the most common types, you have a very wide scope. Provides minimal loss in the transmission of high-frequency radio signals.
- 75 Ohm is also a common type, although somewhat smaller than the previous one. We use it in television technology, which can be explained by the excellent price-to-durability ratio. In addition, losses, in this case, do not matter. In the USA it is used in cable networks.
- 100 Ohm – used very rarely, for special purposes and in impulse technology.
- 150 and 200 ohms – are also used very rarely, they are not provided for by international standards.
Additional elements of the coaxial line
The coaxial path consists not only of the cable itself, additional elements are also used for its device.
Coaxial connectors are also called high-frequency connectors, we have a separate article about them. Necessary for connecting cables to each other, for connecting them to various devices. Please note that some cables may be sold with pre-installed connectors and if the device supports a different format, you will need to purchase an adapter.
Coax adapters, couplers, and tees
Transitions are required to interconnect cables with different types of connectors or to connect to various devices. Tees separate the signal and allow it to be transmitted to several devices (for example, you can connect two TVs to an antenna this way), and taps allow you to create branches, which is most often required when laying cable networks.
Coaxial attenuators are used to attenuate the signal to certain (required) values. There are quite a few types of them, often they are produced for specific tasks, but they are rarely used for domestic purposes.
This device provides a large attenuation of the wave, which passes in a certain direction. In coaxial cables, they are used to absorb the back wave, which can occur in certain situations and is a very undesirable phenomenon.
Additional equipment such as lightning arresters, switches and relays, commutators, baluns, detector heads, and others are also used. But the use of most of this equipment is most often not necessary, so if you are buying a coaxial cable for domestic purposes, then by and large you do not need to know this. Well, specialists who lay complex networks are well versed in such things themselves.
Which coaxial cable to choose for the TV?
Any cables with a wave impedance of 75 ohms of such brands as RK 75, DG 113, SAT 703, RG 6, and SAT 50 are suitable here. They are most often used to connect a TV, you can choose any option. These are quite budget options, however, the signal attenuation will be insignificant (after all, a cable more than 10-20 meters long is rarely required).
Video Surveillance Coaxial Cable
In this case, they very often want to save money on the cable, but in vain. In this case, choosing a cable of poor quality (or one that simply does not match its characteristics) can significantly degrade the operation of the entire system as a whole, making it less efficient. If you answer the question of which coaxial cable for a video surveillance system is better, then the following requirements are here:
- The central conductor is made of copper, it allows you to save the signal over long distances;
- Foil and braid shield, the outer shell will depend on the conditions of use (outdoor or indoor);
- If the cable will be pulled through the air, then a cable is required.
- Wave impedance 75 Ohm.
Much also depends on the distance over which the signal must be transmitted. For example, if it is up to 50-100 meters, then RK-75-1.5 or RK-75-2 (RG-59) is suitable, and if more than 400 meters, then this is RK-75-4 (RG-11 / U ). Also, when laying a coaxial cable for a video surveillance system, we recommend that you follow all the rules and recommendations.
How do determine wave resistance?
Determination of the wave impedance of a coaxial cable is required in cases where an old cable is found that does not have markings and there is no way to find out this parameter. To do this, you need a multimeter that has the function of measuring capacitance.
The capacitance of any piece of cable is measured, after which it is recalculated based on 1 meter. If the wave impedance of the cable is 50 ohms, then the value will be in the region of 95-100 picofarads per meter (Pf / m), if 78 ohms, then from 55 to 65. Possible small deviations from these values, within a few percent. In any case, by measuring the electrical capacitance, you can accurately determine the characteristic impedance of the cable.
How to connect coaxial cable?
A fairly common question, although it is rather difficult to answer it briefly because it all depends on what exactly it will be connected to. In general, everything is quite simple. You need to know the type of coaxial cable, as well as the type of connector on the equipment. Accordingly, you need to choose a suitable connector, if necessary, you need to use adapters.
There are also crimp plugs and bolt plugs. The latter is much easier and faster to mount, but the former is able to provide a better signal quality. However, if we talk about connecting a TV, etc., and the coaxial cable itself is not very long (within 20-30 meters), then these nuances are of no fundamental importance.
What is a Powered Coaxial Cable?
A similar type may also be called a “combined cable”. Its design provides for two power wires, which are also hidden under a layer of the outer shell. This type is often used in video surveillance systems, as well as where it is necessary to connect the power. It allows you to stretch only one cable instead of two, which greatly simplifies installation.
What’s the data transfer rate?
The maximum data transfer rate over a coaxial cable is 10 Mbps. It is for this reason that they are practically not used today in computer systems; by modern standards, this speed is very low.