Decided to do a square inch entry with an idea that I've had floating around for a while. A bit of work with Eagle and I have a PCB designed, a bit of work with a browser & spreadsheet & I have a costed BoM.

I've tried to design it with hand-assembly in mind, so the components aren't as tiny as they could be. I'm sure without that constraint it could fit in a 1/4" square :)

The basic design is tried-and-tested, it's the mixer from my Pi-HF direct conversion receiver kit for the Raspberry Pi. (You can buy a Pi-HF here!) It's using a VHC4053 rather than the HC you might expect because while the HC will handle HF frequencies on its input I find most of them top out around 70MHz and anyway the VHC gives better performance at HF. We need our mixer to be happy with an 80MHz output, the VHC goes up to 120MHz.

The Ethernet transformer is being used as a cheap way to get an RF transformer, and conveniently there are two in the package.

Next step: send off for some PCB prototypes & build a working model.

All the files will be put up under a suitable open hardware licence when finalised so you can build your own. I'll also be selling it as a kit, if it performs well.