You just sent me down yet another rabbithole. Well done.

edit - https://www.essexham.co.uk/news/realtek-sdr-dongle-10-pounds...

Then get even deeper, as we are at thru wall-stuff here is some research: Tan, B; Woodbridge, K. and Chetty, K. (2016) A wireless passive radar system for real-time through-wall movement detection. https://pureportal.coventry.ac.uk/files/7646003/tancomb.pdf

It's a bit more expensive, and requires buying extra antennas.. But this is a coherent SDR built on 4 realtek chips:

https://www.indiegogo.com/projects/kerberossdr-4x-coherent-r...

And you sent me deeper down it.

This seems like a good summing up, more up to date:

https://www.rtl-sdr.com/about-rtl-sdr/

I have far too much to read today. I really could do with a telepathic clone.