Detailed explanation of the types of coaxial cables and how to choose them

Coaxial cables are a type of cable used in a wide range of fields, including communications, broadcasting, and measuring equipment. However, there are so many types of coaxial cables that many people may be unsure which one to use.

This time, we will explain in detail everything from basic knowledge about coaxial cables to how to read product names and the types available. We will also introduce how to choose a coaxial cable, so please use this as a reference when choosing the best coaxial cable.

Basic knowledge of coaxial cables

Coaxial cables are generally sold at electronics retailers. However, there are so many types that it can be difficult to choose the right coaxial cable for your purpose. First, we will explain the basics of coaxial cables.

What is Coaxial Cable?

Coaxial cables are cables designed to efficiently transmit electrical signals, and are particularly good at transmitting high-frequency signals. For this reason, they are used for a variety of purposes, including television antennas, Internet connections, wireless communications, and surveillance cameras.

Another advantage of coaxial cables is that they have a high shielding effect, making them less susceptible to external interference and reducing signal loss. As a cable, it is relatively flexible, so it can be used in narrow spaces and complex wiring paths, and it is highly valued for its high degree of freedom in installation.

Coaxial cable structure

Coaxial cables are made up of four main parts: the center conductor, the insulator, the outer conductor (shield), and the outer jacket. The center conductor carries the signal and is typically made of copper or aluminum. The insulator isolates the center conductor from the outer conductor and prevents signal leakage. The outer conductor, also called the shield, protects the signal from electromagnetic interference (EMI) and ensures signal stability. The outer jacket protects the entire cable and prevents physical damage.

What is a coaxial connector?

A coaxial connector is a device that is attached to the end of a coaxial cable to connect it to other coaxial cables or electronic devices. Coaxial cables require connectors based on specific standards because the center conductor and outer conductor are arranged on the same axis. Coaxial connectors allow for efficient transmission of high frequency signals with minimal signal loss.

There are many types of coaxial connectors, and they are used according to the application. The most common types are F-type connectors, BNC connectors, N-type connectors, and SMA connectors. F-type connectors are mainly used for television antenna cables, while BNC connectors are widely used for broadcasting equipment and measuring instruments. N-type connectors have excellent durability and high-frequency characteristics, and are often used in wireless communication equipment and base stations. SMA connectors are suitable for use in high-frequency bands, and are used in wireless LAN and mobile phone base stations.

What is Impedance?

Impedance is one of the basic characteristics of coaxial cables, and indicates the resistance value when an electrical signal passes through the cable. Generally, 50Ω (ohms) and 75Ω are commonly used. It is good to remember that 50Ω is mainly used for communication and data transmission, while 75Ω is used for television antenna cables, etc. This impedance is usually specified in the product name symbol, and is an important indicator when selecting the use of the cable.

Knowledge of impedance is also necessary to understand the product name symbols described below.

Types of Coaxial Cables

There are many types of coaxial cables depending on the purpose of use. Among them, JIS and MIL standard coaxial cables are widely used. To understand the types of coaxial cables, it is important to check the product symbols. Coaxial cable product symbols are used to convey specific information based on the standards.

Product symbols are important information for instantly understanding the characteristics and specifications of cables. Here we explain the types of coaxial cables, including how to read the product symbols in JIS and MIL standards.

JIS standards

JIS standards are Japanese Industrial Standards for cables. Coaxial cables manufactured based on JIS standards are highly reliable and safe, and are suitable for a wide range of applications.

In the JIS standard, product name symbols are usually composed of a combination of letters and numbers, each of which has a specific meaning.

The meaning of the numbers and letters is as follows:

1. Supported frequencies	If it is compatible with BS/CS broadcasting, the letter "S" will be added. If it is not supported, no characters will be displayed.
2. Cable thickness (diameter)	1.5: 2.9 to 3.4 mm 3: 5.3 to 6.5 mm 5: 7.3 to 8.3 mm 7: 10 to 10.4 mm The thicker the number, the larger the number and the smaller the loss.
3. Cable impedance	C: 75Ω (for TV) D: 50Ω (for wireless)
4. Types of insulators	2: Polyethylene F: Polyethylene foam HF: Highly expanded polyethylene
5. Types of outer conductor and sheath	B: Double braided wire with aluminum foil tape V: Single braid, vinyl W: Double braided vinyl T: Triple braided vinyl

Looking at "S-5C-2V" as an example, it can be interpreted as follows:

S: BS/CS broadcast compatible

5: Thickness 7.7mm

C: 75Ω (for TV)

2: Polyethylene

V: Single braid, vinyl

Single braid and double braid refer to the number of layers of braid on the outer conductor. Double braid means double, and triple braid means triple. Also, the thicker the coaxial cable, the less loss there is, but on the other hand, thinner cables are easier to use.

The thickness and loss guidelines for each JIS standard type are as follows:

Cable type examples	Thickness (outer diameter of outer coating) guideline	Attenuation (loss) guideline
1.5D (50Ω), 1.5C (75Ω)	Approximately 2.9 to 3.4 mm	10MHz @82~106dB /km around
3D (50Ω), 3C (75Ω)	Approximately 5.3 to 6.5 mm	10MHz @35~47dB /km around
5D (50Ω), 5C (75Ω)	Approximately 7.3 to 8.3 mm	10MHz @25~30dB /km around
7C (75Ω)	Approximately 10 to 10.4 mm	10MHz @20~22dB /km around
8D (50Ω)	Approximately 11 to 12.4 mm	10MHz @17~20dB /km around
10D (50Ω)	Approximately 13.1 to 14.7 mm	10MHz @ 14dB/km

MIL standard

MIL standards (Military Specifications and Standards) are standards established by the United States Department of Defense and are widely adopted as standards for guaranteeing the performance and quality of coaxial cables. The part numbers in the MIL standards may look complicated at first glance, but each part has its own meaning. By understanding the part numbers, you will be able to accurately grasp the characteristics and uses of the cable.

MIL standard part numbers are usually divided into several segments. The first segment starts with "MIL-C-17", which indicates that it is a MIL standard coaxial cable. This is an important element that indicates the MIL standard category.

Next comes the string "RG". This stands for "Radio Guide"* and indicates the type of cable. For example, RG-58 or RG-59 are followed by numbers, which relate to the cable's characteristics, especially its impedance and diameter. RG-58 has an impedance of 50Ω and RG-59 has an impedance of 75Ω, and their uses are the same as those explained in the JIS standard.

*Some say it stands for Radio frequency coaxial cable General purpose.

Furthermore, the numbers and letters that follow indicate more specific characteristics. For example, the symbols "A/U" and "B/U" refer to the version or improvement of the cable. "A" is the first version, "B" is the improved version, and "U" stands for "Universal" and indicates that it is suitable for general use.

Other symbols may be added to indicate the type of outer jacket material or shielding, for example "PTFE" means polytetrafluoroethylene coating, which can be used in high temperature environments.

If it is "RG-58A/U", it can be interpreted as follows:

RG: Radio Guide

58: Model number (unlike the JIS standard, it is based on the order of establishment, not the thickness)

A: Assignment symbol (assigned in alphabetical order)

U: Universal

An example of a MIL-spec cable is shown below.

Cable Example	Thickness guide	Features
RG-174/U	Approximately 2.5mm	This cable is thinner than 1.5D cable and is easier to handle.
RG-316/U	Approximately 2.4mm	A high-quality cable that uses Teflon-based materials for the insulation and outer coating.
RG-58/U	Around 5.0mm	A 3Ω cable that is slightly thinner than 50D. RG-58A/U has a twisted central conductor.
RG-62/U	Around 6.2mm	Impedance 93 Ω cable. RG-62A/U has a non-migratory PVC outer jacket. In addition, the materials, structure, and dimensions are often the same.
RG-8/U	Around 10.3mm	A 8Ω cable that is slightly thinner than the 50D.
RG-14/U	Around 13.8mm	10Ω cable equivalent to 50D. Double braided for close to 10-2W.

High frequency measurement cable

High-frequency measurement cables are used in systems that require precision and reliability, especially in measuring signals in the high-frequency band. The frequency band covers 18 to 60 GHz, and since they transmit extremely high frequencies, their electrical and physical characteristics are strictly controlled.

In addition, high frequency measurement cables can be attached to small high frequency connectors such as "SMA" and "N". The connectors are also designed for use in high frequency bands, and require strict mechanical precision and electrical characteristics.

In addition, temperature characteristics are also an element that must be considered. Since high-frequency measurements are often performed under harsh environmental conditions, it is important that the cable can maintain stable performance regardless of high or low temperatures. For this reason, materials with excellent heat and cold resistance are often selected.

Semi-flexible

Semi-flexible cables combine the best parts of conventional flexible and rigid cables to achieve a balance between flexibility and stability. Semi-flexible cables use an insulator with a specific shape between the inner and outer conductors, which allows them to maintain both flexibility and excellent electrical performance.

Semi-flexible cables are excellent at transmitting high-frequency signals, and are widely used in applications such as measuring instruments and high-frequency test equipment. They have a relatively small bending radius and can be easily handled in tight spaces, making them easy to install and wire. They are also lighter than rigid cables, yet have excellent shielding performance.

In addition, it supports frequency bands from 18 to 40 GHz, and can also be fitted with small high-frequency connectors.

Semi-rigid

Semi-rigid cables are characterized by their flexibility while still having a certain degree of hardness. They are compatible with frequency bands from 18 to 50 GHz and demonstrate excellent performance in transmitting high-frequency signals. They can operate at higher frequencies than flexible cables and are also suitable for use in high-frequency bands of 20 GHz or higher.

Semi-rigid cables have better shielding and less attenuation than semi-flexible cables. Their excellent shielding performance effectively prevents external electromagnetic interference.

Another feature of semi-rigid cables is their ease of processing. Semi-rigid cables can be bent, so you can adjust their shape to suit the installation location. However, they cannot be bent as freely as flexible cables, so they must be handled with care. In particular, if you need to use a narrow space or complex wiring, be sure to check the shape of the bend in advance.

Semi-rigid cables also have the advantage of being resistant to high temperatures and mechanical stress, and their high durability allows them to provide stable performance over a long period of time.

How to Choose a Coaxial Cable

Here are some points to keep in mind when choosing a coaxial cable for yourself. We recommend selecting a coaxial cable in the following order:

1. Impedance
2. frequency band
3. Cable thickness
4. cable length
5. Cable stiffness

First, it is a good idea to decide on the type of connector that matches the device you want to connect, and then select the coaxial cable.

1. Impedance

JIS standard coaxial cables are divided into 50Ω and 75Ω depending on the impedance. When selecting the impedance, choose according to the transmitting and receiving equipment and antenna. If you want to purchase it for a TV, choose "75Ω", and if you will use it for data communication or wireless, choose "50Ω".

If you mistakenly use a cable with a different impedance, signal reflection and loss may occur, resulting in a significant drop in communication quality. Therefore, it is important to select a cable that meets the impedance standards of the equipment and system you are using. In particular, when using high-frequency bands, impedance matching is an important factor that determines communication performance.

2. Frequency band

Coaxial cables are designed to work optimally within a specific frequency range, and different types of cables are suitable depending on the frequency band you are using. For example, relatively soft and thick cables are suitable for use in low frequency bands (below a few MHz), while higher frequency bands (above a few GHz) require stiffer and thinner cables to minimize signal loss.

In addition, the cable's shielding performance must be considered according to the frequency band. High-frequency bands require cables with high shielding performance against external electromagnetic interference (EMI) and radio frequency interference (RFI). High shielding performance helps maintain signal purity, preventing communication errors and data loss.

Also, when selecting a coaxial cable, check the cable's transmission loss (attenuation). Since transmission loss increases as the frequency increases, select a cable with low transmission loss for use in high-frequency bands. For example, it is important to select the optimal cable for each frequency band according to the specific application and environment, such as 5 GHz Wi-Fi communication or satellite communication.

3. Cable thickness

Coaxial cables are also available in a wide variety of thicknesses. The thickness of a coaxial cable has a significant impact on its signal transmission performance and ease of handling. Thick cables have low resistance and are excellent for long-distance signal transmission, but are difficult to handle and lack flexibility. On the other hand, thin cables are easy to handle and are suitable for tight spaces, but their high resistance can lead to greater signal attenuation.

When choosing the thickness of the cable, it is important to consider the equipment to be used, the installation environment, and the required performance. For example, if you are using high frequency bands or need long distance transmission, it is recommended to choose a thicker cable. Also, if the installation environment is narrow and it is difficult to handle the cable, a thinner cable is recommended.

4. Cable length

The length of the coaxial cable is an important factor that has a significant impact on the quality of the signal. A cable that is too long will weaken the signal, especially when handling high-frequency signals. Therefore, it is best to choose the minimum length necessary.

When deciding on the length of the cable, it is also necessary to consider impedance matching. If the impedance of the cable and the device to be connected do not match, it will cause signal distortion. Please pay particular attention when using cables over long distances.

It is also important to choose the appropriate length for the cable's intended use. For home use, a short, easy-to-handle cable is suitable, but for commercial or long-distance use, a high-quality cable must be selected to prevent signal attenuation.

5. Cable stiffness

The harder the coaxial cable, the more durable it is, and the more resistant it is to external physical impacts and abrasion. Therefore, it is suitable for use in fixed installations and environments where it is not frequently moved. For example, a stiff cable is effective when wiring inside a building or connecting to a fixed antenna. However, stiff cables are difficult to bend, so they are not suitable for narrow spaces or complex wiring.

On the other hand, flexible coaxial cables are highly flexible, so they can fit into tight spaces and complex wiring paths. They are easy to install even when the cable needs to be bent or twisted. Flexible types of cables are suitable for equipment that is moved around a lot or where wiring needs to be changed frequently. Flexible cables are also useful for laboratory experimental equipment and movable antennas. However, be careful as soft cables are vulnerable to physical impact and abrasion.

Summary

Coaxial cables are used for a variety of purposes, so choosing the right one is very important. In particular, you can choose a cable that will perform optimally by considering the type of signal, distance, and environmental conditions. Also, a better understanding will help you make a better choice.

How to choose a coaxial cable varies greatly depending on the application and purpose. With basic knowledge, you can choose the most suitable cable and use it effectively. By correctly reading the cable name symbols and understanding the cable types and standards, you will be able to build a more reliable communication environment.