The Main Characteristic of Coaxial Cable ( Part One)
(1). characteristic impedance
Coaxial cable is mainly composed of internal and external conductors. There is resistance and inductance for current flowing in conductors, and conductance and capacitance exist between conductors. In cable TV system, the characteristic impedance of the coaxial cable required is 75 Omega, but the characteristic impedance of the coaxial cable is usually (75 + 5) Omega. Therefore, in order to prevent the signal reflection and achieve the best transmission effect, the terminal load impedance should be equal to the characteristic impedance of the cable as much as possible.
(2). attenuation characteristics
The attenuation characteristic of coaxial cable is usually expressed by the attenuation constant, that is, the decibels of the unit length (such as 100M) cable attenuates the signal. The attenuation loss of a signal in a coaxial cable is related to the size, dielectric constant and working frequency of the coaxial cable.
The attenuation constant is proportional to the square root of the working frequency of the signal f. That is, the higher the frequency, the more attenuation constant; the lower the frequency, the smaller the attenuation constant.
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