Bluetooth instead of USB for Android interfacing

Yeah, I could have used Bluetooth. It would have reduced the complexity on the software side - no libusb - but I still would have used the NDK to build the codec and modem C code for Android, so it wouldn't have eliminated all of the native code.

It would have upped the complexity on the hardware side too. I would have to digitise the sound, so that means an ADC, and then interfaced that ADC with the Bluetooth device. That probably means another microcontroller, so more software to write. I'm also not sure if using Bluetooth Audio with a compression-less codec, as required to not distort the modem tones, would have been possible.

So yep, there were a bunch of other options for getting the radio signals off the air and into the phone, but a USB soundcard is a neat one for digtising and transporting the samples into the phone.