Know-how

How to avoid phone conversation crosstalk. The importance of cables.

how-to-avoid-phone-crosstalk-cables-quality-sampsistemi

Crosstalk is a quite common undesired phenomenon that annoy most of people during their conversation on the phone. In the past years, several technical developments have contributed to reduce the crosstalk incidence on voice circuit, however, the real and definitive control on it is a proper cable design, quality and manufacturing.

Crosstalk occurs when one voice circuit picks up the signal from another circuit making the conversation jumping from wire pair to the other. A different twisted rate reduces the possibility of crosstalk issue.

The signal transmitted in the cable is in the form of current and it produces an interference electromagnetic field that can cause noise in the near cables. So, the twist operation plays a pivotal role in order to remove the electromagnetic interference from wires.

The wires twisted with and along each other carry equal and opposite amount of current through them. Therefore, the interference produced by one wire is cancelled by the interference produced by other wire since they are equal and opposite in nature. Since during this operation each twisted pair color combination is assigned a unique twist gear.

Thus, the design and manufacturing of the cables are fundamental in order to produce high quality cables without interference while in action. In doing so, twisting machine must ensures:

  • constant lay-length
  • minimize wire stretching to avoid the alternation of electrical feature of the wire
  • constant winding tension
  • avoid the scratching of the wire insulation and the correct winding around twisted cables of the shielded tapes.

In order to increase the performance and efficiency of the process, it is possible to build within the cradle a spark tester to check the product quality and take appropriate action.

Important is also the payoff system, which must ensure the correct cable tension at the input of the twisting machine. It is therefore necessary to have a motorized payoff with synchronized dancer and tension control system.

Coaxial cables mfg process, the main parameters.

coaxial-cable-manufacturing-process

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.

How cable television works

how-cable-television-works-sampsistemi

Nowadays, cable television refers to any system that distributes signals through coaxial or fiber optic cables. Cable television was used in the USA in the late 40s to improve reception of commercial network broadcasts. Since then, there has been a proliferation of cable television systems offering special services.

Cable system bandwidth has increased with the increase of the program options. As technology progressed with fiber optics and analog to digital conversion, quality and feature improved. Coaxial cables can carry many different channels into homes on a single RG-6 coaxial feed. However, it is also possible to use thicker RG-11 coaxial cables for high definition cable service as well as for the internet.

Coaxial cables are manufactured to meet the increasing requests of high speed data and video. They are flexible and suitable for extreme environmental conditions. In order to avoid signal distortions or interferences, the coaxial cables must be manufactured ensuring high quality of the final product. The choice of material and manufacturing process is essential to produce a coaxial cable which does not have any problems in its final application.

Designing a drawing and extrusion line for high quality coaxial cables is a straightforward process that, however, requires a deep understanding of the final product, application and specific needs of the end user. Television cable as coaxial cables are composed of wire conductor and different insulation layers including a foamed section, each of them serving a specific purpose. The braided wiring can be made in aluminum or copper and is the part which carries the actual signal in a radio frequency format. The wiring is covered by sheath specifically designed in order to prevent incoming interferences and signal leakage. Thereafter, over the sheath, it is also possible to put a metallic layer which strengthens the prevention of signal interference. To sum up, the outer layer must be:

  • Thick;
  • Durable;
  • Resistant in order to withstand all environmental conditions.