Thank you to Lincoln Boggs (KF8DPW) for submitting his open source RTL-SDR Blog V3 shield footprint PCB design, which is available on GitHub.

This PCB serves as a bare-bones starter design that precisely matches the footprint of the RTL-SDR Blog V3, allowing you to develop custom addon boards. The current layout provides connections to GPIO, I2C, CLK, and several other pins on the RTL-SDR Blog V3 that are exposed for experimental and bespoke projects. As Lincoln explains:

Recently in my spare time I have been looking into developing an open-source project for the RTL-SDR blog dongles, more specifically an addon board system similar to RPi hats and arduino shields through the I2C pins.

So far, I've gotten a board footprint published on GitHub for the V3's pins.

The idea is to allow easy addition of modules like external clocks, sensors, controller boards, or even something like a LoRa chip all with minimal soldering and easy swap-ability. I also plan to design 3D models of cases for the SDR to allow it to look cleaner or be more portable in different senses.