The Datavideo CB-3 or CB-4 are 5-pin XLR 20m or 50m extension cables for the ITC-100 intercom system. This will enable you to extend the existing tally cable by another 20m or 50m, depending on which cable you purchase! The CB-3 or CB-4 can also be daisy-chained together to form extensions of 40m, 60m, 80m, etc up to 200m(eg of CB-3). For a longer extension cable, please choose for above drop down when ordering. CB-4 50m extension cable .