What is coaxial cable loss? Explaining the causes and how to understand it

Coaxial cables are an important communication medium widely used for transmitting video and audio signals, but their performance is affected by various factors. "Coaxial cable loss" is one of the factors that has a significant effect on signal quality and transmission distance.

This article provides an easy-to-understand explanation of the causes and methods of understanding coaxial cable loss. It is recommended for use by anyone who uses coaxial cables or is involved in communication systems.

What is Coaxial Cable Loss?

Coaxial cables always incur losses when transmitting signals. These losses cause signal attenuation and distortion, which is an important factor in the design and operation of communication systems.

Coaxial cable losses are mainly divided into two types: skin effect loss and dielectric loss. These losses vary depending on the cable length and the frequency used, so appropriate cable selection and design are necessary. Understanding coaxial cable losses will help you build a more efficient communication system.

Skin effect losses

Skin effect loss is a loss caused by the phenomenon that high-frequency signals flow near the surface of a conductor. As the frequency of a signal increases, the current tends to flow preferentially near the surface of the conductor.

This reduces the effective cross-sectional area of ​​the conductor and increases its resistance, which results in some of the signal energy being converted into heat, which appears as losses.

Skin effect loss increases in proportion to frequency, so care should be taken when using in the high frequency range. To reduce the skin effect, it is important to select the conductor material and shape appropriately.

Another method is to use cables with multi-core or lamellar structures to increase the surface area of ​​the conductors.Thicker cables or special conductor structures with larger surface areas may be used.

Dielectric Loss

Dielectric loss is the loss caused by the insulation (dielectric) within a coaxial cable. When a high-frequency signal passes through the insulation, its molecules react to the signal's electric field and vibrate, converting some of the energy into heat in the process.

This phenomenon attenuates signal strength and appears as loss. Dielectric loss depends on the material of the insulator and the frequency of the signal, and the higher the signal frequency, the greater the loss tends to be. To reduce dielectric loss, it is important to select a low-loss dielectric material and optimize the thickness of the dielectric.

In some cases, dielectric losses can be significantly reduced by using specially constructed cables that use air dielectrics.

Main Causes of Coaxial Cable Loss

Coaxial cable loss is caused by a combination of several factors, the main causes being the length of the cable, the material it is made of, and the frequency used, in addition to the skin effect and dielectric loss.

First, the conductor resistance of the cable is a factor in loss. The resistance value changes depending on the material and thickness of the conductor, which affects the attenuation of the signal. Also, low quality insulation increases loss.

Physical stress caused by bending or squeezing the cable can also increase loss, and environmental changes in temperature and humidity can affect the cable's characteristics and cause loss to fluctuate.

Furthermore, as frequencies increase, signal transmission becomes more difficult and tends to result in greater losses. By understanding these factors and taking appropriate measures, losses can be minimized.

How to understand coaxial cable loss

Accurate understanding of coaxial cable losses is critical in the design and maintenance of communications systems, as proper evaluation of losses can optimize system performance and prevent problems before they occur.

The main causes of loss are the skin effect and dielectric loss, but to know specifically how much these affect communications, actual measurements are essential. This article provides a detailed explanation of "coaxial cable loss measurement" and "cable transmission testing" as methods for understanding loss.

Coaxial cable loss measurement

When measuring loss in coaxial cable, specific measuring equipment is used to determine how much the cable actually attenuates the signal, typically specialized equipment such as a network analyzer or a time domain reflectometer.

A network analyzer sends a signal of a specific frequency to the cable and measures its reflection and transmission characteristics, allowing you to accurately determine the insertion loss and return loss for each frequency.

Additionally, Time Domain Reflectometry (TDR) can be used to pinpoint discontinuities or damage in the cable. These instruments allow detailed analysis of the loss distribution over the length of the cable, as well as the loss characteristics at specific frequencies.

Cable Transmission Test

Cable transmission testing is a method to evaluate the performance of cables under conditions close to actual usage conditions. It verifies whether the cable can transmit signals properly, especially in high-frequency signal transmission. The test transmits and receives signals, and checks for loss, noise, delay, etc. during transmission.

Specifically, bit error rate (BER) measurements and eye pattern analysis are performed. BER tests compare the transmitted and received signals to measure the error occurrence rate. Eye pattern analysis allows visual evaluation of the quality of digital signals.

These tests will allow you to understand the actual performance of your cable and allow you to modify the cable or take additional measures if necessary.

Summary

Coaxial cable loss is an important factor that greatly affects the performance of a communication system. It mainly consists of skin effect loss and dielectric loss, which vary with frequency and operating environment. The causes of loss are varied, including the physical properties of the cable, environmental conditions, and signal characteristics. Proper cable selection and design can minimize these losses.

Loss can be effectively understood by using measuring instruments such as network analyzers and TDRs. It is also possible to estimate it through theoretical calculations, but for important systems it is recommended to use actual measurements.

By properly understanding coaxial cable losses and dealing with them appropriately, you can build a more efficient and reliable communications system.