[Jeri Ellsworth] has been working on a direct conversion receiver using an FPGA as an oscillator and a PC sound card DSP. Being the excellent presenter she is, she first goes through the history and theory of radio reception (fast forward to 1:30), before digging into the meat of the build (parts 2 and 3 are also available).
Instead of ‘old school’ receiving sets, the functionality of a software-based radio can be changed by just modifying the program. Building one of these receivers doesn’t use many parts, but the math and programming behind the radio can be pretty intense. Everything is fed into an off-the-shelf PC sound card for processing. The 16-bit sound card [Jeri] used covers 22kHz of radio bandwidth, but that can be increased to 48kHz with a 24-bit card.
The build itself is just a small circuit that goes between the antenna, but we have to respect [Jeri]‘s ability to deal with that amount of analog madness. There’s also a great PDF on software-designed radio that [Jeri] linked to explaining everything in a non-youtube format. This receiver is pretty impressive considering we’ve come a pretty long way over the past century.