The essential function of coaxial cables is to transmit high frequency energy and signals with low loss, with reflectionless matching and without phase and amplitude distortion. For such transmission, characteristic impedance and attenuation are important concepts. characteristic impedance (zo) is determined by the ratio of dielectric od to conductor diameter, hence a large cable and a very small cable can have the same zobut the smaller cable will have higher losses. The problem in high energy transmission is the losses because of i) cable dielectric, ii) cable construction, iii) radiation, and iv) interference with adjoining circuits.

PTFE insulated multi-core cables are required mainly for high-reliability and high-temperature interconnections for signal and controlapplications. We refer to a case where we manufactured a special cable for British Nuclear Energy to control a Nuclear Robotic Arm. This cable had 28 members, some for sensing temperature, some for audio signals, some for video signals, a few for operating the lights inside the reactor, a number of others for activating the motor, and so on. Even though most common cables would not have such a large number of applications in a single construction, it is sufficient to illustrate the varied uses of multi-core cables.

Silver Plated Copper (SPC) for use up to 200°C (minimum 1 micron silver coating as per ASTM-B-298) Nickel Plated Copper (NPC) up to 260°C (minimum 1.25 micron nickel coating as per ASTM-B-355) Silver Plated High Strength Copper Alloy (SPHSCA) for mechanical strength in fine cross-sections and for superior flex-life (somewhat lower conductivity than copper) generally as per ASTM-B-624 Pure Nickel for use up beyond 260°C; very high resistance to corrosion; DC resistance about 6 times that of copper at 20°C Resistance alloys for Thermo-Couple applications

Silver Plated Copper Clad Steel (SPCCS) commonly used for RF coaxial cables) as per ASTM-B-501 Spiral multi-strands on glass-fibre cord for high linear resistance -- generally for heating applications Plain copper or Tinned copper can not be used due to high-temperature processing and applications; tin melts and flows into the interstices of stranding to make the conductor inflexible; copper tends to oxidize and become brittle

Silver Plated Copper (SPC) for use up to 200°C (minimum 1 micron silver coating as per ASTM-B-298) Nickel Plated Copper (NPC) up to 260°C (minimum 1.25 micron nickel coating as per ASTM-B-355) Silver Plated High Strength Copper Alloy (SPHSCA) for mechanical strength in fine cross-sections and for superior flex-life (somewhat lower conductivity than copper) generally as per ASTM-B-624 Pure Nickel for use up beyond 260°C; very high resistance to corrosion; DC resistance about 6 times that of copper at 20°C Resistance alloys for Thermo-Couple applications