How to Choose the Right Coaxial Cable | Technology Writer

How to Choose the Right Coaxial Cable

16 Dec 20120 comments

Whether you are assembling your computer or your home theater or almost anything else electronic, proper cabling is a fundamental component. This is especially true when building an elaborate electronic project, such as a media center system, or home theaters  Proper cabling is the key to a successful job.

Co-axial cables are considered to be the best cabling system for communication and data transfer applications. However, with so many types of coax cabling available today, it is important to know which one to choose, and for what purposes.

Coaxial Cable Structure
The coaxial cable generally refers to cables that have a single central solid copper cable (wire), which is surrounded by insulation. The insulation is then surrounded by a mesh or braided foil type conductor. The insulation separates the braid from the core copper cable, and has dielectric properties. This dielectric nature of the cable actually has a large effect on the performance of the cable and its conductivity. This whole ensemble is then covered with an insulating jacket, which serves to protect the cable from external stress, dirt, and interference. Generally, the data transmissions occur through the central copper wire, while the braided cabling acts as the ground.

Impedance Factor
The main factor that determines the nature of the coaxial cable is its impedance factor. Impedance is the term given to the level of power transfer and attenuation that the cable can attain, with respect to the cable length. The main factor to consider here is that the impedance level must be the same at both ends of the cable for optimum performance and delivery.

Generally, there are three main standard values of impedance that coaxial cables come with: 50 ohms, 75 ohms, and 100 ohms. The 50 ohms and the 75 ohms coax cables are the most common and most popular types. The best-loss impedance level is between 52-64 ohms, while the best power handling is achieved at an impedance value of 30 ohms. Hence, choosing the right cable for the right job is extremely important.

Also, the coax cables have limitations in terms of maximum length. The RG59/U type has the least maximum distance of 750 feet, while the RG11/U type coax cable can go up to 1500 feet.

So which coax cable do you need?
Selecting the right coaxial cable is essential to gain the best performance from the devices. Here are a few examples of the applications and uses of the different types of coax cables available today:
  • RG-59: The RG-59 Coax cable is a thinner cable and of relatively lower grade. Almost all coax cables look the same outwardly. The RG-59 is easily bombarded by interference, such as electromagnetic or radio interference and, hence, this cable can only be used as a basic cable due to its non-suitability for anything else, except maybe base television services.
  • RG-6: This is a higher-end cable, with much better shielding. This makes it suitable for more applications, such as the connection between the satellite dish and the set top box, for instance. The cable is best suited for the purpose mentioned above, as it operates efficiently above 50Hz.
  • RG-8: This cable comes with an impedance value of 50 ohms, and is best suited for applications, such as Amateur Radio or other HF options.
  • RG-174: This cable deserves special mention, as it is quite flexible and has an impedance of 50 ohms, and is commonly used as pigtails for Wireless Fidelity Antennae. However, it has a high-loss factor, making it unsuitable for other applications.
  • H155: This cable is a low-loss cable, which is suitable for high radio frequency applications, such as amateur radio and radio-based communication.
Coax cables support data transfer speeds from 10 to 100 MB/s (Megabytes per second), and can use several different types of connectors. However, the most popular connectors are UHF, BNC and the N-type connectors.

UHF connectors, as their name suggests, are optimized for Ultra High Frequency Radio applications. The plug is named as 'PL259', while the socket is termed as 'SO239'. This connector is suitable for low-loss applications, and sports threaded screw mounting mechanisms for easy installation. However, this cable has relatively inconsistent impedance ratings and, hence, is used only in applications, such as Public Address Systems, CB Radio, or Amateur Radio.

The BNC is a male type with a rotating ring that helps to securely screw it to the base. This connector is suitable for coax cables with impedance values of 50 and 75 ohms. It also has straight and angled variants, allowing for use in a variety of situations.

The N-type connector is a high performance connector, designed to be of use in RF applications, such as broadcast and communications. Just like the BNC, this connector is available in 50 and 75 ohms types. The connectors are designed in such a way that the two types cannot be mixed. The connectors are capable of handling high power, and the cable is designed for standard operation up to 11GHz.

Coaxial Cable
Coax cables are the way to go when data transfer or communication-based projects are being undertaken. With a lot of options to choose from, the best type of cable to select depends upon the need or application for which the cable will be employed. The right impedance value can spell the difference between an excellent job and a disastrous output. Once you determine the application in which the cable will be used, the above mentioned cables, their descriptions and usage scenarios will give you a clearer idea about which cable to go for.

Authors Bio: Christopher Parkinson originally studied microprocessor design theory before testing phone lines and repairing faulty circuit boards for a couple of telco companies. His interest in electronics started at an early age when he used a screwdriver to open up a video game console to see how it worked. These days Chris is a home electronics enthusiast who enjoys tampering with the latest technology when not writing about the latest Raspberry Pi kits from Newark.

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