Open-source boards designed in KiCad by HB9UF on GitHub, from 3 repositories. A board’s address here is its repository’s there.
HB9UF/ElPiHat
EchoLink Hat for Raspberry Pi
HB9UF/rf_detector
Simple dual RF detector, with large SMD parts
HB9UF/SignalSnitch
An RF detector kit with THT parts