Comment by _paulc

It looks like it is a Direct Conversion (Zero IF) rather than a Direct Sampling Receiver [0] - ie. it uses does a quadrature LO to down convert to baseband I/Q (in this case a Taylor QSD as a mixer). The RP2040 ADC bandwidth is only 250KHz.

[0] https://www.analog.com/en/resources/technical-articles/a-rev...