[TomVDB]

The RTL-SDR is only an RF front-end that brings down the desired RF signal to a baseband frequency, followed by an quadrature AD converter, followed by a USB interface.

All the DSP operations are already done by the Raspberry Pi.

http://aaronscher.com/wireless_com_SDR/rtl_sdr_info.html

In the diagram above, it shows “DSP” but that’s just two basic multiplications and a low pass filter. It doesn’t do any heavy lifting.

If you want to get rid of the RTL-SDR, you’d need that analog RF block and the AD converter inside the Pi. That doesn’t make a lot of sense of a general purpose SOC.