[foundart]

arrl.org and rsgb.org, the US and UK amateur radio organizations, sell a variety of books you might find helpful.

If you are in the US, ARRL sells books that teach to the specifics of the US tests. I used those but found them rather unsatisfying. There are other books which focus on experiments (see Hands-On Radio Experiments) and others on theory.

The ARRL Handbook is also useful. It's updated annually, but you won't miss too much if you save a few dollars by getting an older edition.