Coaxial cable temperature characteristics

We know that coaxial cable is composed of inner conductor, outer conductor, insulation medium and sheath. The outer conductor has two basic functions: the first is the effect of the return conductor and the second is the shielding effect. Insulating media (ie, physical foaming) and jackets all play a role of insulation, protection, and shielding. When the temperature changes, it is not a decisive factor for the loss of the entire cable. The inner conductor is an important part of the signal transmission, so the cable signal attenuation is mainly caused by the loss of the inner conductor resistance.

Copper is the main material of the inner conductor, and there are mainly two kinds of foamed copper wire and copper clad aluminum wire. In our CATV system, we mainly use the material of foamed copper wire. This material can easily locate the inner conductor at the center of the insulation medium, making the inner and outer conductors truly “coaxial” and improve the transmission characteristics of the cable. However, copper has inherent metal (material) characteristics, which also led to it as the culprit in cable signal attenuation.

First, the attenuation in the coaxial cable is related to the resistance (ie, the inner conductor). The resistance of a conductor is a property of the conductor itself, and its size depends on the material, length, and cross-sectional area of ​​the conductor. In addition, the temperature has a great influence on the resistance of the conductor. For most conductors, the higher the temperature, the greater the resistance; for a few conductors, the temperature rises and the resistance is smaller. Copper belongs to the former, and when the temperature rises, the resistance increases; when it decreases, the resistance decreases. Therefore, according to the laws of physics (metal properties), we can think that the inner conductor (copper) of a coaxial cable also conforms to, or follows this rule, that the temperature is high, the impedance is large, the level is reduced, the temperature is low, and the impedance is small. The level increases. The temperature change has a great influence on the copper conductor (coaxial cable), which is also a metal (physical) characteristic of copper, and there is no way to solve it, but we can choose to compensate with an active device with a temperature compensation function. To reduce the impact of temperature changes on the cable, improve the user's viewing results.

As stated, no one system can withstand such strong level fluctuations and changes. If the signal level rises or falls by about 6 to 10 dB, the user's demand cannot be satisfied if a better method cannot be used to compensate. Therefore, for long-distance trunk lines, we must try to change its original design and rationalize it (such as changing to fiber-to-the-building). However, as the temperature changes, the impact on cable levels is a difficult technical problem for cable systems. Therefore, the effective use of temperature compensation amplifiers is the best and most practical method of existing CATV systems.