If you want to know everything that's worth knowing about VOR and ADF, an Aussie bloke by the name of Russ Evans (actually W. R. Evans), former Senior Examiner of Airmen of the NSW Region of the old Dept. of Civil Aviation in Australia, produced 2 very worthy tomes - the first on VOR and the second on ADF.
I've just tried a Google search without success but maybe I'm looking in the wrong place. Perhaps someone else on here might have a better idea on how to acquire these very worthy books. I still have my own copy of each and used them both to learn about the aids and to teach them to others, so can highly recommend them!
