3 3 . 9 8 0   M Hz ▁and ▁an ▁output ▁of ▁ 4 6 . 1 4 0   M Hz ▁is ▁a ▁same ▁band ▁repe ater . ▁ ▁In ▁same ▁band ▁repe aters , ▁a ▁central ▁design ▁problem ▁is ▁keeping ▁the ▁repe ater ' s ▁own ▁transmit ter ▁from ▁inter fer ing ▁with ▁the ▁receiver . ▁Red uc ing ▁the ▁coupling ▁between ▁transmit ter ▁and ▁input ▁frequency ▁receiver ▁is ▁called ▁isol ation . ▁ ▁Du plex er ▁system ▁ ▁In ▁same - band ▁repe aters , ▁isol ation ▁between ▁transmit ter ▁and ▁receiver ▁can ▁be ▁created ▁by ▁using ▁a ▁single ▁anten na ▁and ▁a ▁device ▁called ▁a ▁du plex er . ▁The ▁device ▁is ▁a ▁tun ed ▁filter ▁connected ▁to ▁the ▁anten na . ▁In ▁this ▁example , ▁consider ▁a ▁type ▁of ▁device ▁called ▁a ▁band - pass ▁du plex er . ▁It ▁allows , ▁or ▁passes , ▁a ▁band , ▁( or ▁a ▁narrow ▁range , ) ▁of ▁frequencies . ▁ ▁There ▁are ▁two ▁legs ▁to ▁the ▁du plex er ▁filter , ▁one ▁is ▁tun ed ▁to ▁pass ▁the ▁input ▁frequency , ▁the ▁other ▁is ▁tun ed ▁to ▁pass ▁the ▁output ▁frequency . ▁Both ▁legs ▁of ▁the ▁filter ▁are ▁couple d ▁to ▁the ▁anten na . ▁The ▁repe ater ▁receiver ▁is ▁connected ▁to ▁the ▁receive ▁leg ▁while ▁the ▁transmit ter ▁is ▁connected ▁to ▁the ▁transmit ▁leg . ▁The ▁du plex er ▁prevents ▁de grad ation ▁of ▁the ▁receiver ▁sens itivity ▁by ▁the ▁transmit ter ▁in ▁two ▁ways . ▁