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What is a coaxial cable and what is the coaxial cable used for?

(Summary description)Coaxialcablesareoftenusedfordevice-to-deviceconnectionsorinbus-typenetworktopologies.Thecentralaxisofthecoaxialcableisacopperwire,plusalayerofinsulatingmaterial.Theouterlayerofthisinsulatingmaterialis

What is a coaxial cable and what is the coaxial cable used for?

(Summary description)Coaxialcablesareoftenusedfordevice-to-deviceconnectionsorinbus-typenetworktopologies.Thecentralaxisofthecoaxialcableisacopperwire,plusalayerofinsulatingmaterial.Theouterlayerofthisinsulatingmaterialis

Information

 

Coaxial cables are often used for device-to-device connections or in bus-type network topologies. The central axis of the coaxial cable is a copper wire, plus a layer of insulating material. The outer layer of this insulating material is surrounded by a hollow cylindrical mesh copper conductor, and the outermost layer is an insulating layer.Compared with twisted pair cable, coaxial cable has strong anti-interference ability, good shielding performance, stable data transmission, and cheap price, and it can be used without connecting to a hub or switch.

Coaxial cables can be divided into baseband coaxial cables and broadband coaxial cables in terms of use. Coaxial cables are divided into 50Ω baseband cables and 75Ω broadband cables. Baseband cables are divided into thin coaxial cables and thick coaxial cables. The baseband cable is only used for digital transmission, and the data rate can reach 10Mbps.
 

 Characteristic impedance of coaxial cable


A coaxial cable is made up of two different core conductors separated from each other by an insulating material. The inner conductor is copper-clad aluminum or copper core wire, and the outer conductor is an aluminum tube or metal braided mesh sheath. If the outer conductor is grounded, it will act as a shielding layer for the center conductor and have the effect of resisting external interference. In coaxial cable transmission theory, it can ensure that radio frequency is transmitted inside the cable. Due to the close distance between the inner and outer conductors, there will be certain cables between each other. In fact, the inductance and capacitance are evenly distributed along the transmission line. So the characteristic impedance of the transmission line depends on the inductance and capacitance of the line, which in turn depends on the size of the line.

 

 Attenuation characteristics of coaxial cable


The attenuation constant of a coaxial cable reflects the magnitude of the loss when electromagnetic energy is transmitted along the cable, and is one of the main transmission characteristics of a coaxial cable. Signal attenuation in a transmission line is caused by distributed capacitance and distributed inductance in the transmission line. The attenuation in a coaxial cable is frequency-dependent. As the frequency increases, the inductive reactance of the series inductance increases, and the capacitive reactance of the parallel capacitor decreases. When the signal is transmitted in the cable, after a certain distance, the signal will become weaker and weaker, and the attenuation of the signal will become attenuation. The higher the frequency, the greater the loss.

 

 Characteristics of coaxial cable


Ambient temperature change is the main cause of signal level fluctuations in cable television systems. Because the characteristics of coaxial cables are closely related to changes in ambient temperature, especially the long trunk lines of large systems are more prominent, the quality of system transmission performance will vary with Changes in temperature. When the ambient temperature rises, the corresponding cable loss also increases more. Ambient temperature change is one of the most important factors that cause signal level changes in cable television systems. Temperature mainly affects the DC resistance and dielectric loss of coaxial cables. When the ambient temperature increases, the loss of the conductor and the medium in the cable increases as the frequency increases; when the temperature decreases, the loss of the conductor and the medium in the cable also decreases. Because temperature has a greater impact on cable loss, special attention should be drawn by maintenance staff.

 

 Selection and use of cables


Coaxial cables are commonly used to transmit cable television signals, video signals, digital signals, and various other high-frequency signals. Depending on the application, there are differences in the standards for selecting cables.

Good-quality cables have a tight, firm structure and a smooth, flexible outer sheath. The woven mesh is thick and dense. Except for the number of braided wires, the braiding angle of the shielding layer is less than 450. However, in order to save materials, some manufacturers have a braid angle of the cable greater than 700, which will make the shielding characteristics of the cable worse. Poorly crafted cables can be pulled out of the center conductor or insulation. The aluminum foil of the outer conductor of the four shielded cable is divided into two types: bonding and lapping. Lapping is a layer of aluminum foil on the physical insulation of the cable, and the joint overlaps a part, usually 3mm. Bonding is the bonding of aluminum foil and physical foam insulator. Bonding is better than lap shielding. The best four-shielded cables use bonding.

The coaxial cables used in cable television systems and high-frequency broadband monitoring systems are mostly high-frequency physical foaming cables. Because the low-frequency anti-interference characteristics of the cable are poor, the external interference intensity in the low frequency band is large and the interference frequency is large. Therefore, the frequency band below 5MHz was intentionally avoided in use. However, the frequency bandwidth of the above system works, so when choosing a cable, special attention should be paid to the attenuation characteristics and reflection loss of high frequencies. When the cable TV transmits the signal in the reverse direction, the noise of all the terminals will be collected to the front end. Therefore, in order to minimize the interference of the cable from the outside, a 4-layer shielded or aluminum tube cable is usually selected.


If you are interested in coaxial cables, you can check https://www.hdg-telecom.com/cable-1 for more information obout specific cable types or Sales@hdg-telecom.com directly.

 

 

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Time of issue:2021-04-28 10:55:44
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