SD (software-defined) radio receivers use a bare minimum of hardware, relying instead on their software capabilities. This SDR project demonstrates what’s achievable, in this case a multi-purpose receiver covering all bands from 150 kHz to 30 MHz. It’s been optimised for receiving DRM and AM broadcasts but is also suitable for listening in to the world of amateur transmissions.

www.nti-online.de/diraboxsdr.htm
www.sdradio.org
sourceforge.net/projects/drm
www.g8jcf.dyndns.org