Relay operated, 900 ohms input impedance, 600 ohms output impedancetwo-way operation, two-wire transmission, crosstalk, plus 50 db, minus 48v DC , 880 ma, 0 to 50 degrees c, operation power rqmt, 12.812 in. H, 19.000in. W, 8.500 in. Deep, o/a dim., designed for mtg on a 19-inch rack