Cable shielding and pair twisting ensure the integrity of the audio and video signal against possible EMI and RFI (Electromagnetic Interference and Radio Frequency Interference) around the cable. Cables can be shielded or unshielded, except coaxial cables where, by definition, require a single shielded conductor.
Shielding types:
Spiral Shield: Spiral shield is “wrapped” around the cable. These shields can be single or double. They are more flexible than braided shields and easier to terminate. Because of their spiral structure (coils), they can show inductance effects and are therefore not suitable for high frequencies. Normally used for analogue audio signals frequencies. With flexion, these types of shield tend to open losing effectiveness especially at high frequencies.
Braid Shield: The braid shield provides superior structural integrity while maintaining good flexibility and durability. These shields are ideal for minimizing low frequency interferences and at radio frequencies have a lower DC resistance than the tape shield.
The coverage that can be obtained with a single braided shield can be 95% and with a double braided shield it can reach 98%. With a braided screen, it is not physically possible to reach 100% coverage.
Foil Shield: Foil shields can be made of metal or copper but the most common is the aluminium-polyester tape. Foil shields can provide 100% coverage. Because these types of shields are too thin to be used as a contact point, a wire called the Drain wire is run along the shield, close to it. This is the contact point. Due to the fact that the wavelength on high frequencies can travel through the holes of the braid shields, this type of shield is the most effective at high frequency.
Combination Shields: Different types of shields can be combined in one cable, bringing together the different properties of each one.
For example: Foil + Spiral, Foil + Braid, Foil + Braid + Foil or Foil + Braid + Foil + Braid
In the following document, you will find more information about cable shielding:
