E19 Smart vehicle mounted wireless FM transmitter car USB playback dual USB 2.4A car charger1. Wireless specification: Wireless V4.2.2. L.W.H.: 90*35*35 mm, weight: 38g.3. Supply voltage: 12V-24V, USB output: 5V / 2.4A.4. FM frequency: 87.5-108 MHz.5. Support USB playback (32G MAX), support format: MP3, WMA.6. After connection to phone Wireless, tune up an empty channel on the car FM, and then tune up the same empty channel on the Wireless transmitter, this way you can connect.