Trying to Store Audio

I want to use the Si4703 as an FM receiver, and then take that incoming signal and then store it on an Sd card. This is because my project idea is to use fm radio signals as a way of communication in short distances over empty radio stations. so i have a transmitter that can transmit at different frequencies but now i want to find a way for my receiver to store the transmission.

I want to avoid having to store the received signal by putting a microphone near the speaker and just writing that to an SD so i thought that there might be a way to store the direct signal as soon as something is being received

Im not using this to record radio, and ideally I will be testing this project in an environment where there are as little music fm radio stations as possible.

Any help?