It can be seen that the constant Z 0 , defined in the above equations has the dimensions of impedance (ratio of voltage to current) and is a function of primary constants of the line and operating frequency. It is called the “characteristic impedance” of the transmission line, and conventionally denoted by Z 0 . Z 0 = R + j ω ω L G + j ω ω C = L C 1 − − j ( R ω ω L ) 1 − − j ( G ω ω C ) which holds generally, for any transmission line. For well-functioning transmission lines, with either R and G both very small, or with ω ω very high, or all of the above, we get Z 0 ≈ ≈ L C hence the characteristic impedance is typically very close to being a real number. Manufacturers make commercial cables to approximate this condition very closely over a wide range of frequencies.