While not directly realted to SWL, this looks to
be a usefull, and FREE tutorial on various aspects
of electronics, covering basic analog circuits, AD,
and my favorite, "Ground Loop".

I am sure that at some point they are going to
demonstrate how perfect their test equipment is.
And I have no doubt that if you can afoard it, it
would would be killer gear.

http://zone.ni.com/devzone/conceptd.nsf/webmain/53C91BF3110AD6E786256F51005F09C4

Terry