The growth of wireless and high-speed data applications has led to the use of coaxial cable over traditional video and telecom cables. With the development and standardization of coaxial cables for various applications, coaxial cables have become commonplace in homes, offices, telecommunication facilities, railroads, industrial plants, and government/public safety facilities. This diversification of applications has led to a diversification of coaxial cable types, ratings and manufacturers.
Recommendations for selecting coaxial cables
The following TST CABLE recommendations and frequently asked questions will help you make the right choice in coaxial cable for your specific needs.
Understand the application requirements and parameters
The beginning of everything is always to understand the problem to be solved. In the case of coaxial cables, this means understanding the quality of the signal that the cable will carry. Some of the important factors are the frequency range and the power level of the signal being transmitted. Other factors include the RF and electromagnetic environment through which the signal is traveling, the length of the cabling, and the difficulty of the cabling. The project budget and all the institutional requirements surrounding the selection of a particular coaxial cable for an application also play an important role in the decision.
Choosing the Right Impedance
The two main impedances used in coaxial cable are 75 ohms and 50 ohms. The impedance of a coaxial cable cannot be determined externally unless there is a visible marking element. If these two impedances are confused, it is possible to cause damage to the equipment connectors or the device itself, or at least degrade the performance of the system. Although sometimes used in crossover, 75-ohm cables are typically used for video applications, while 50-ohm cables are more commonly used for data and wireless purposes. The type of equipment and devices to be connected determines the cable impedance to be used.
Selecting the correct cable length based on attenuation
Signal energy can be lost due to thermal energy caused by conductor resistance, dielectric loss factors, and other factors related to the quality of the coaxial cable material. The attenuation of a coaxial cable indicates the energy loss per unit length of cable. For applications where signal power is extremely low or cabling is required to be extremely long and no amplifiers or signal boosters are installed, low loss cables may be required to meet the minimum signal strength requirements at the receiving end of the coaxial cable. If the attenuation of the coaxial cable is low enough to eliminate the need for a signal booster, the use of low-loss cable can be a cost-effective investment, even if the cable is expensive.
Cable Performance Depends on Frequency
Each coaxial cable’s specification lists a number of performance parameters, including attenuation and power handling, that vary with frequency. In general, the higher the signal frequency, the more resistive losses it suffers, and therefore the greater the degree of attenuation. In addition, at certain high enough frequencies, coaxial cables operate as waveguides and very poor TEM mode transmission lines, which is known as the cutoff frequency. This cutoff frequency is much higher than the highest frequency of any signal to be transmitted.
Different cables have different power ratings
Depending on the cable diameter, the type of central and outer conductor and the quality of the cable, different cables have different rated maximum processing power. These ratings are given in the form of values under continuous wave conditions, average or peak values and have different meanings depending on the type of signal carried. It is also possible to give ratings for rated maximum voltage and rated maximum current. It should be noted that such ratings also depend on the frequency and that a cable with a good safety margin should be selected. Once the rating of a coaxial cable is exceeded, there is a risk of unfortunate failure modes such as electrical sparking, accelerated aging, dielectric degradation, and combustion can occur.
Not all coaxial cables have the same shielding properties
Coaxial cables are available in braided, stranded, foil, solid, corrugated, and many other construction types, with a variety of outer conductor types, as well as a variety of shielding methods. To further minimize received or emitted interference, some coaxial cables may have multiple shielding layers in addition to the outer conductor. Additionally, the use of different types of outer conductors and shields allows for flattening resistance, higher stiffness/flexibility, and lower attenuation. For many applications, the higher the quality of the outer conductors and shields of a coaxial cable, the better, and the more of them the better, budget permitting.
How is it routed/aligned?
Different applications typically have very different cabling needs. The cabling requirements for large outdoor industrial environments are not the same as those inside a machine facility or an airplane fuselage. From cabling inside equipment assemblies to cabling inside complex buildings, there is a coaxial cable to meet the needs of almost any environment. For specific types of cabling, coaxial cables have several technical parameters that measure their ability to meet the requirements, including: bend radius, maximum load or unsupported cabling scenarios, wind loading, and a variety of environmental factors and ratings. Typically, this information should be provided to the cable purchaser, otherwise the exact details of the cabling requirements can be as important as the electrical properties of the cable. Different jacketing materials and protective coatings are also used to assist in cable installation, as some applications make wiring a more delicate operation.
What type of connectors are required?
Similar to coaxial cables, coaxial cable connectors come in a wide variety. The type of coaxial connector is determined by the device, system, or other interconnect to be mated to the coaxial cable. However, depending on the size, type of shielding, type of center conductor, additional layers, and type of metal used, certain cables may be more suited to certain types of connectors. Among other things, since contact between conductors of different metals can lead to corrosion and degradation of performance and ultimately to failure, it is important to prevent such contact from occurring.
When using non-specialized coaxial connectors, some coaxial cables may be oversized or undersized. Many manufacturers offer optimized coaxial connectors for specific cables, and low-PIM or low-loss applications require the use of dedicated, high-performance connectors. In addition, coaxial connectors and cables can be connected in a variety of ways, including crimping, soldering, and tool-less press-fitting. One point that should be considered is that not all cables are suitable for certain connection types.
Should I buy coaxial cable or coaxial cable assemblies?
Due to the variety and application requirements when installing coaxial connectors with cables, many suppliers offer pre-assembled coaxial assemblies for specific applications. If the cable length, performance parameters and type of coaxial connector are known for a particular application, then the best choice is to use a cable assembly.
Institutional Requirements and Specialty Equipment
Certain industry applications, such as military, government, avionics, aerospace and industrial equipment, have specific regulations and require specific coaxial cable performance. Cables can only be used in these areas if they meet the requirements of these industry, societal and governmental standards. These requirements can be quite complex and it is not easy to comply with their industry standards, and the TST CABLE experts may be the best people to consult when you come across such cables.
Specialty Cables
Test and measurement, scientific experiments, satellites, high-performance radar and many other special applications require the use of very specialized coaxial cables. In addition to the institutional standards mentioned above, these cables often need to fulfill application-specific and many non-standard requirements. Experts can help purchasers look at cables that meet specific needs on a case-by-case basis and ultimately select the best option.
Be wary of the proliferation of counterfeit cables and knockoffs
Unfortunately, illegally sold counterfeit coaxial cables have become more accessible to the buying public due to the profit motive. The practice of using cables other than the real thing is inherently illegal and potentially puts the safety of operators and equipment at risk. By choosing a qualified supplier like TST CABLE with good credit and an excellent production quality management system, companies can prevent the potential losses and hazards caused by counterfeit coaxial cables.