The early history of radio is quite fascinating, and luckily, lots of books from this early period are out of copyright and are available for free on the Internet. As an example, check out The book of wireless telegraph and telephone by A. F. Collins. This was radio in its infancy, when the use of vacuum tubes to create continuous oscillations was “the new wireless”, and the majority of stations were still using spark gaps. While you can’t legally operate spark anymore, it is still interesting to read these kinds of books, which offered pragmatic advice to the experimenters of the day on how they could construct and deploy their own wireless stations. Very nice.

The book of wireless telegraph and telephone : being a clear description of wireless telgraph and telephone sets and how to make and operate them, together with a simple explanation of how wireless works.