This adapter adjusts the antenna power voltage of overseas tuners, such as TBS tuners, to match domestic specifications (reducing 18V to approximately 15V). It connects between the tuner and the antenna via coaxial cable connectors. Inside, it consists of a diode placed between the connectors (see product photos). Due to the diode connection, there is a specific direction for connecting the tuner and antenna. Please connect the tuner and antenna according to the direction indicated on the diode. The case has a lot of empty space, so a USB-connected TBS 5520se, for example, might be able to be installed inside. The front cover of the case can be removed. Thank you for viewing.