This SainSonic radio repeater is a useful device for increasing the distance of radio communication. Theoretically, the valid communication distance of radio on the market is up to 8KM. But the distance can be highly shortened in actual utilization because of some obstructions like building, cave, mountain, etc. This repeater is easily used and just need to connect transceivers with it. It is commonly applicable for cave construction, undermine construction, field construction, transmission between basement and ground, large-scale activity, long distance transmission, etc. Specifications * 4 ports for transceivers * Suitable for Kenwood interface * Battery not needed * No adjustment for transceiver * Easy to use: connection with transceivers only * Mode of operation: Semi-duplex Package List 1 x SainSonic RepeaterNote: There"s no user manual. If you need video instructions, please search on Youtube.