First - monitor your audio:

http://www.nu9n.com/scope_your_audio.html

Next - RTTY tuning. There is much more info available online:

http://lists.contesting.com/archives.../msg00237.html

Two-tone test generator. I prefer 1000 and 1800hz, but any non-harmonically-related pair will work:

http://www.circuitsarchive.org/index...Tone_Generator

Poor man's spectrum analyzer/panadapter:

http://www.science-workshop.com/

I'll see if I can find more.