- A filter inserted into a communications line, so as to remove undesired signal components, or to otherwise selectively transmit or reject signals in one or more intervals of frequencies. For example, a line filter must be installed at all jack points of telephone devices in the premises where an ADSL line is present, to prevent high frequency components from causing interference when talking or exchanging faxes. The jack point connected to the ADSL modem must not have such a filter.
- A filter which prevents the passage of noise signals in a power line, thereby improving the operation of the devices connected to said line. It does so by attenuating radio frequency noise, while permitting the 50 or 60 Hz current to pass. Also called power-line filter.