Testing the voltage of coaxial cables is typically performed for one of two reasons: to verify appropriate voltage on voltage-carrying coaxial cables or to troubleshoot sources of distortion on your TV signal. Voltage can be coming from the cable lines, the TV or the environment. Testing is done with a voltmeter, and it's a lot like how ordinary wires are tested.
Disconnect the coaxial cable from the TV or cable box and position it for easy access.
Set the voltmeter to read AC (alternating current) voltage.
Touch one probe of the voltmeter to the center wire. At the same time, touch the other probe to the shielding, which will be the outside area that screws into the coaxial stud.
Read the display on the multimeter to determine the voltage.