The 859901 is a splitter which allows you to split signal from a repeater to over 2 or more internal antennas. The coverage area of each antenna will be half of the coverage area of a single antenna, which equates to 70% of the coverage distance. This is useful if you wish to improve signal in 2 separate locations, or on 2 separate floors. Cellular repeaters typically only improve signal on the floor that they are installed, so the splitter is useful for those with multi-leveled homes.