SDR with a transmitter see reference here -> https://github.com/F5OEO/rpitx
rpitx is a general radio frequency transmitter for Raspberry Pi which doesn't require any other hardware unless filter to avoid intererence. It can handle frequencies from 5 KHz up to 1500 MHz.
Rpitx is a software made for educational on RF system. It has not been tested for compliance with regulations governing transmission of radio signals.