In order to perform at their most, coaxial cables must be manufactured following a high quality designing process. In addition, there are a number of parameters which must be kept in mind during the manufacturing process. The main ones are listed below:
- Characteristic Impedance “Zo”
- Capacitance “C”
- Attenuation “α”
- Power rating
- Velocity of propagation “Vp”
In particular in high frequency transmission systems, it is important that the characteristic impedance “Zo”, expressed in Ohm, corresponds to the one of the receiving system. Any difference of characteristic impedance at the junction will have a considerable effect on the quality of the signal. Likewise, distortions and signal losses could be affected by an inconstancy of the conductor quality, cable geometry and dielectric uniformity.
Capacity “C”, measured in Farad, is important to understand the capacity of a dielectric material within conductors with potential differences to keep the dielectric charge. Cables with low capacitance are more suitable for data transmission lines, so that it will make a transmission at longer distances possible. In order to maintain this feature the material used has a low dielectric, such as polypropylene.
The Attenuation “α”, measured in dB, is necessary since it determines the transmission level of the line. It is the ratio of the input voltage and the output voltage. The attenuation results are signal voltage losses and slowing down of the pulse. The two factors which provoke attenuation are:
- Resistive loss of conductors
- Loss in the dielectric
The heating and softening of the dielectric have an impact on the transmitted power rating. In fact, the heat loss is directly proportional to the frequency, dielectric constant and dissipation factors. Thereby, the power rating relies on 3 elements:
- Cable dimension
- Ambient temperature
- Voltage reflection
The velocity of propagation “Vp”, measured in percentage, represents the period required by a signal to pass through a transmission line.
Therefore, an approximate coaxial cables’ manufacturing process will provoke dimensional or material irregularities along the line and consequently affect the feature impedance. A portion of signal will be lost at each impedance deviation. Reflections increase as the frequency goes up.
The cable industry uses the uniformity of return loss as an indicator for evaluating the cable’s quality.
However, the market prefers to use the Structural Return Loss (SRL). So, the manufacturing phases are extremely important for the final quality of the product. There are many parameters and elements to take into consideration, these are just a few. However, their description marks the importance of choosing a supplier of extrusion lines who knows the subject well and has a broad expertise.