The RG cable (Radiofrequency - Government), is a coaxial cable used to transport high frequency signals that has at least 2 concentric conductors , a central one, called the nucleus, in charge of carrying the information, and an outer one, with a tubular appearance, called the mesh, shield or braid, which serves as a ground reference. Sometimes there is more than one shield, this being a conductive foil. Between them there is a dielectric insulating layer, on whose characteristics the quality of the cable will mainly depend. The whole assembly is usually protected by an insulating cover (also called an outer jacket).
As coaxial cable that it is, it is a type of transmission line that is used to transport these high-frequency electrical signals with low losses, the impedance of the cable must match that of the system that sends the signal and that of the one that receives it , so that there are no transmission losses, so the characteristic impedances of these cables are 50, 75, 93 ohms All coaxial cables are defined with the letters RG (Radio Frequency - Government) followed by a number (type) and the letter U (Universal) or A / U, B / U, etc. that indicate successive modifications and substitutions to the original type.
In the end, it is a standardization of all these types of RG cables, regardless of the manufacturer, that is regulated by the MIL-C-17 standard. The MIL-C-17 standard is very strict with the frequency response of the cables, so these standards specify both internal and external dimensions and / or the dielectric, characteristic impedance of the cable, maximum losses or attenuation, maximum power, capacity, speed of propagation.