About RT97S: Channel switching; long press the button for three seconds to switch channels; if you need to adjust the volume; try to press the button briefly RT97S vs RT97; RT97S has a DB-9 female connector; which can be directly connected to the microphone and is compatible with Raspberry Pi; enabling multiple RT97S repeaters to be interconnected to extend the communication distance (additional components are not included in the package) GMRS; 8 default GMRS channels; If you need customized frequency; please contact us via email Extend the distance; RT97S helps to connect emergency calls outside the range of the walkie talkies; and is suitable for outdoor activities; remote mountainous areas; large-scale farms.