Excelsus Z-330TJA Z-Blocker DSL Line Filter Meets ANSI T1.421 for excellent voice quality and performance Filters one or more phone devices sharing a single jack Blocks DSL/HPN signals from phone equipment to enhance voice-band signal Isolates DSL/HPN from phone equipment impedance for peak data performance Ideal for blocking RF interference from DSL/HPN for uninterrupted data streaming