50 ohm impedance
High-frequency cables usually have an impedance of 50 ohms. This value was already specified in the 1930s for coaxial cables in which high RF power of several kilowatts had to be transmitted.
br> Such coaxial cables were used in transmitter technology. In addition to 50-ohm cables, there are also RF cables with an impedance of 75 ohms, but these are mainly used in video technology.
Opting for 50-ohm impedance is considered a good compromise between the RF power to be transmitted and low attenuation. For a 10-mm RF cable, the minimum attenuation is 77 ohms. The corresponding characteristic curve shows increasing attenuation values for both lower and higher impedance. This is due to the fact that the diameter of the inner conductor enters logarithmically into the impedance, inversely proportional to the shielding diameter.
However, the impedance value decreases with higher dielectric constants of the dielectric.