A great place to get some books on this is at "believe it or not" radio
shake.
I saw three at a Frostburg State University Conference I attended and
they were wonderful.
They are little things, hand written or so they seem to be, and
wonderfully illustrated with examples and formulas, the whole shebang.
I did look for them at a local radio shack and they were all sold out so
they must be as good as they seemed.
Beth