Coaxial Cables for Digital, Terrestrial, Satellite and Interactive TV
IMC produces a wide range of coaxial cables, made according to national, European and international norms as well asaccording to customerâ€™s specific requirements.
They are used for high frequency transmission and in various application fields: the military, medical andcommunication sectors. The coaxial cable is a transmission line allowing the propagation of an electric signal. As it is a passive element, itresults in an attenuation of the signal which passes along it proportional to the length of the cable and the operation frequency.
Some of the main features of the transmission line are:
- contained attenuation
- impedance regularity
- contained reflexion coefficient
- Return Path (frequency ranging between 5 MHz and 42 MHz)
- good resistance to possible mechanic stress
- good protection of the transmitted signal from possible external interferences
- optimum resistance to atmospherical agents
The basic components of a coaxial cable are:
- Inner conductor
The function of the inner conductor is to carry the signal; the greater the diameter the less the resulting attenuation.It can be single or stranded, made of copper, copper- plated steel or tin-plated copper to facilitate soldering and to protect it from corrosion. It can also be made of silver-plated copper to improve the propagation of the signal, taking full advantage of the â€śskin effectâ€ť.In radio frequency the signal is propagated along the external surface of the conductor and the higher the frequency,
the smaller the propagation thickness on the conductor.
The dielectric is the extruded insulating material around the inner conductor, its main function is to maintain the outer conductor (screen) concentric with respect to the inner one. It is made of Polyethylene (PE).
- Solid Polyethylene extrusion
- Extrusion GAS-INJECTED foam Polyethylene
The Solid Polyethylene extrusion has the advantage of being more resistant from the mechanical point of view,compared to PEE GAS INJECTED, guaranteeing the coaxiality between the conductors; the PEE GAS INJECTED extrusion, thanks to the process of inert gas (azote) foaming, produces a lower dielectric constant (approx. 1,40) and so the loss angle is smaller. Gas foaming also guarantees a better stability of attenuation values, keeping them constant overtime even in critical conditions such as for example in the presence of humidity or sudden changes in temperature.
The dielectric of the ideal coaxial cable is air.
The tape, where used, forms part of the screen of a coaxial cable, guaranteeing a total screening coverage (120%). It can be of two types:
- Al/Pet (formed of a aluminium foil and a Polyester film)
- Al/Pet/Al (formed of two Aluminium foils and a Polyester film)
- Al/Pet/Sy (formed of Aluminium foil, Polyester film and Copolymer)
It results in a remarkable improvement of the efficiency of the screening, guaranteeing:
- protection of the signal which passes along the cable from possible external electromagnetic fields;
- protection of the external environment from radiation produced by the cable itself.
Because of the constant increase in the use of electromagnetic waves and high power/charges used in the industry an integral screen is necessary in order to minimize problems of interference.
The braid is characterized by the number of wires, by the cross size of these wires and by the pitch of the braiding; it influences not only the efficiency of the screening but also the transfer impedance. The evaluation parameter for the construction of the braid is the coverage percentage given by the following formula:
%Kc = [2 * Kf â€“ Kf2] * 100
- Kc = coverage factor
- Kf = filling factor
The filling factor is given by the following formula:
- m = total number of spools
- n = number of wire strands per spool
- d= diameter of the braid wire
- D= average diameter of the braid
- L= braid pitch
The sheath is made of Polyvinyl Chloride (PVC) or Polyethylene (PE). The sheath has two main functions:
- protecting the cable
- keeping the outer conductor (screen) tight to the dielectric thus making both capacitance and impedance constantalong the whole cable.
The PE sheath is used for laying cables underground.
IMC also produces a series of coaxial cables with a LSZH (Zero Halogen Compound) sheath.