Just a thought but I recently found out that many of these SDR’s do not fully implement the circuitry required for direct sampling mode.
It is not supposed to be that difficult to get working but if you are making boards might as well put it into the design.
I thought about this during the design, and absolutely would have included some connector, even just as test points, for the unused i input… if I had the space. After a full redesign (rearranging the tuner, rtl2832u, using a smaller eeprom, etc.) I expect it would be possible, but I’m happy with it currently since I can pull out my SDRPlay if I want to go below 24mhz. The connections are already marked in the schematic if anyone wants to add them to their own design though.
Some models add some extra components (filters, a balun, etc.) to allow the same connector to be used for both the tuner and direct sampling. Adding that would be even more difficult, maybe impossible without putting components on the back, but could be possible. I have no plans to add that to this card.