Coaxial cable: practical suggestions and common problems

The growth of wireless and high-speed data applications has caused the use of coaxial cables to surpass traditional video and telecommunications cables. With the development and standardization of coaxial cables used in various applications, coaxial cables have become common equipment in homes, offices, telecommunications facilities, railways, industrial plants, and government/public safety facilities. The diversification of such applications has led to diversification of the types, grades and manufacturers of coaxial cables.

Coaxial cable application requirements and parameters

The beginning of everything is always to understand the problem to be solved. For the purchase of coaxial cable, this means that you need to know the quality of the signal that the cable needs to carry. Some of the important factors are the frequency range and the power level of the transmitted signal. Other factors include the radio frequency and electromagnetic environment through which the signal passes, wiring length, and wiring difficulty. Around the specific coaxial cable selected for a certain application, the project budget and all institutional requirements also play an important role in decision-making.

1. Correctly select impedance

The two main impedances used in coaxial cables are 75 ohms and 50 ohms. Unless there is a visible marking content, the impedance of a coaxial cable cannot be judged from the outside. If the above two impedances are confused, it may cause damage to the device connector or the device itself, or at least degrade system performance. Although sometimes used crosswise, 75-ohm cables are often used for video applications, while 50-ohm cables are more commonly used for data and wireless purposes. The type of equipment and device to be connected determines the cable impedance to be used.

2. Correctly select the cable length according to the attenuation

Signal energy can be lost due to thermal energy caused by conductor resistance, dielectric loss factor and other factors related to the quality of the coaxial cable material. The attenuation of a coaxial cable represents the energy loss per unit length of the cable. For applications where the signal power is extremely low or the wiring requirements are extremely long, and there is no amplifier or signal booster, a low-loss cable 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 so low that there is no need to use a signal booster, even if the price of the low-loss cable is more expensive, the use of the cable is still a cost-effective investment.

Different cables have different power ratings

Depends on the cable diameter, the type of central and outer conductors, and the quality of the cable. Different cables have different rated maximum processing powers. These ratings are given in the form of values under continuous wave conditions, average values or peak values, and have different meanings depending on the type of signal carried. In addition, it is possible to give the rated values of the rated maximum voltage and the rated maximum current. It should be noted that such ratings also depend on the frequency, and cables with better safety margins should be selected. Once the rated power of the coaxial cable is exceeded, there is a risk of unfortunate failure modes such as electric sparks, accelerated aging, medium degradation, and combustion.

Not all coaxial cables have the same shielding performance

Coaxial cables have a variety of structure types such as braided, stranded, foil, solid, corrugated, etc., a variety of outer conductor types, and a variety of shielding methods. In order to further reduce the interference received or emitted, some coaxial cables can have multiple shielding layers in addition to the outer conductor. In addition, the use of different types of outer conductors and shielding layers can also achieve crush resistance, higher rigidity/flexibility and lower attenuation. For many applications, when budget allows, the higher the quality of the outer conductor and shielding layer of a coaxial cable, the better, and the more the number, the better.

How to wire/route?

Different applications usually have very different wiring requirements. The wiring requirements for large outdoor industrial environments are different from those in machinery facilities or aircraft fuselages. From wiring in equipment assemblies to wiring in complex buildings, for almost any environment, there is a corresponding coaxial cable that can meet its needs. For specific wiring types, coaxial cables have several technical parameters to measure whether they can meet the requirements, including: bending radius, maximum load or unsupported wiring conditions, wind load, and a variety of environmental factors and ratings. Normally, such information should be provided to the cable purchaser, otherwise the exact details of the wiring requirements may be as important as the electrical performance of the cable. Because some applications make the wiring operation rougher, different sheath materials and protective layers are usually used to assist in cable installation.

What type of connector do I need?

When using non-dedicated coaxial connectors, some coaxial cables may have problems with oversize or undersize. Many manufacturers provide optimized coaxial connectors for specific cables, and low PIM or low loss applications require the use of dedicated high-performance connectors. In addition, the coaxial connector and the cable can be connected by crimping, welding, and toolless press-fitting. One thing to consider is that not all cables are suitable for certain connection types.

Should I buy a coaxial cable or a coaxial cable assembly?

Due to the diversity and application requirements of coaxial connectors and cables during installation, many suppliers provide pre-assembled coaxial components for specific purposes. For a specific application, if the cable length, performance parameters, and coaxial connector type are known, then the best choice is to use cable assemblies.

Institutional requirements and special equipment

Certain applications, such as military, government, avionics, aerospace and industrial equipment, have specific regulations and requirements for coaxial cable performance. Only by meeting the institutional requirements of these industries, society, and governments, can cables be qualified to be used in these fields. These requirements can be quite complex, and it is not easy to remember them. Experts may be the best candidates for details here.

Special cable

Many special applications such as test and measurement, scientific experiments, satellites, high-performance radars, etc. require the use of very special coaxial cables. In addition to the above-mentioned institutional standards, these cables usually need to meet specific applications and many non-standard requirements. Experts can help purchasers understand the cables that can meet specific needs one by one, and finally choose the best option.

Counterfeit cables and counterfeit goods

Unfortunately, due to profit-driven, counterfeit coaxial cables sold illegally are more accessible to the buying crowd. The use of cables other than genuine ones is illegal in itself and may put the safety of operators and equipment at risk. Only choosing qualified suppliers with good historical records and quality management systems is the best measure to prevent potential losses caused by counterfeit coaxial cables.