Changing the processor to something like a Teensy would allow for more digital modes to be added.? As it stands, CW is about all the Arduino is able to decode.? For something like PSK-31 more clock cycles and a better ADC are required.? I haven't checked the pin-out, but I would think that a few jumpers or even a PCB buffer would be enough to swap the Nano for some other development board.? This would also open up more options for digital filters and user interfaces.
Keeping the DDS and micro controller/processor separate from the main board allows for more flexibility in this regard, and I'd be happy to leave it that way.? On-board refinements for the BitX40 that stick with the original design goal of making a board for experimentation and customization might include adding even more places for people to plug into the signal, like in the IF, or refining what's already there (widening the bandwidth of the crystal filter comes to mind.)
