Using Proxmark3 as a simple RFID reader and reading frequency and amplitude

Hi, I want to Use Proxmark3 as a simple RFID reader and reading frequency and amplitude. I want to gather the exact frequency between tag and proxmark3, and use proxmark3 as a software defined radio, is it possible?

My another question is how to use proxmark3 hardware and code it myself with simple codes, is there any instructions?