75 ohm impedance
High-frequency cables generally have an impedance of 50 ohms or 75 ohms. The 50-ohm imp edance has its origin in RF power transmission, such as from an RF transmitter to the antenna. It is a compromise between attenuation and transmitted power.
br> It is different with the 75-ohm impedance. Coaxial cables with this impedance are used where no power needs to be transmitted. For example, in cable television or in video technology.
The impedance of 75 ohms has the lowest possible attenuation of a coaxial cable. This is exactly 77 ohms and was rounded off to 75 ohms. It should be added, however, that the dielectric constant of the dielectric influences the impedance. As the dielectric constant increases, the impedance value for the lowest attenuation falls.