Coax Cable Characteristic Impedance Explained
All feeders possess a characteristic impedance. For coaxial cable there are two main standards that have been adopted over the years. These are 75 Ω and 50 Ω.
The 50 Ω coax cable is used for professional and commercial applications whereas the 75 Ω coax cable is used almost exclusively for domestic TV and VHF FM applications.
The reason for the choice of these two impedance standards is largely historical but arises from the properties provided by the two impedance levels: