How to Determine the Characteristic Impedance of a Cable

Sometimes you get your hands on an unmarked coaxial cable. To find its characteristic impedance, you can use a RigExpert antenna analyzer or any other no-name one.

But it turns out to be much simpler than that: all you need is a caliper and a calculator.

For example, take an RG-213 cable with a 2.7 mm center conductor and a 7.5 mm foamed polyethylene dielectric (1.5). Plug the values into the formula (log(7.5mm/2.7mm)/sqrt(1.5))*138 Ohm = 49.9 Ohm