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Analysis of case detection technology of coaxial cable

Information Source:Henan Huadong Cable Co., Ltd  Release date:2014-03-21

One, coaxial cable detection
1, after the water change on the cable characteristic impedance we do a test, when the cable of water moisture, the TV signal through the cable, the level is lower than the stipulated loss value of cable. According to the cable inlet, wetting time, cable conductor corrosion, rust and oxidation degree is different, the level of loss attenuation values will be different.
The damp, water coaxial cable SYDY-75-9.5 bamboo different do all the testing records.
1) test instrument: MT500 multimeter; MC7 spectrum; DL6243 capacitance and inductance tester.

Test items: (2) 100 m cable)
• cable DC resistance;
• cable capacitance, inductance;
• level.

Two, the test results
Through the experiment, the cable of different degrees of water moisture, will lead to corresponding changes in the distributed capacitance, inductance, the characteristic impedance will change, because of the presence of the electric field between inner and outer coaxial cable of two conductors, certain capacitance, generated in the conductor inductance certain through alternating TV signal, the inductance, capacitance distribution in the cable, capacitor to measure inductance and series parallel such as inductance L and capacitance C per meter coaxial cable, formed the characteristic impedance of Z coaxial cable

From the characteristic impedance variation formula, an inductor L and a capacitor C will lead to the change of impedance. From the analysis of cable capacitance and inductance measurement data after the water. The amount of water more, change of capacitance, inductance is bigger, its characteristic impedance will change, characteristic impedance the impedance and cable signal input range, called mismatch. Finally, results in power loss increases, the part of signal power loss.

From the theoretical analysis, the attenuation is mainly caused by the inner conductor "skin effect" Loss Coaxial cable. The higher the frequency skin effect is stronger, the series inductive reactance (wL) increased, while the capacitive shunt capacitance (WC) decreases, the bypass inner conductor signal external conductor increased leakage, so the higher the frequency, the more long cable transmission distance, the greater the attenuation. The cable damp, water, the measured data prove that, inductance and capacitance (capacitance increase in magnitude than large inductance), and the series inductance inductance (wL) is on the increase, capacitive shunt capacitance (WC) was decreased, the bypass signal external conductor on the inner conductor of the leakage increased the signal level, the more amount of attenuation decrease. The cable damp, each channel level decreased significantly after water, but different frequency the attenuation is not a level after level, water like changes like the wave, much depends on its degree of variation in the cable damp water.

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