First don't push the transmit button without an antenna. If you have coax cable try building an antenna (https://youtu.be/KASWnflEX_0) about grounding just make sure you are connecting the ground screw from the unit to a proper ground.

Also you could buy something like this one: https://www.amazon.com/dp/B07BDJ8HN9/ref=cm_sw_r_cp_apa_i_lir4Eb3FXR3V2

Are you using a car battery or a power supply to test your unit?