Interference from devices or the environment can travel along the outer conductor of a coaxial cable as a common mode current. This current creates a common mode disturbance that can impact the upstream integrity of a cable plant. SCTE 249 is the test method used by the cable industry for measuring the amplitude and frequency of these disturbances.
Common mode filters (or attenuators) can be used to attenuate the amplitude of these disturbances. This test method creates an industry accepted standard for testing the attenuation of these common mode filters.