Hi, I've built and used this one: http://www.cpinternet.com/~lyle/proto/LFproto.htm#LFconv It uses a crystal and a double-balanced mixer. Cheap to build, works great. I can't tell you how it works at slow speeds because the radio I was using at the time was not stable enough for that. I was able to copy WWVB easy, the stuff at 24 kHz, plenty of NDBs, etc. Eric