There is a 1955 book called "Probes", author Zucconi, Library of Congress #54-13280. It's old, but there's about 220 pages - worth taking a look at
http://www.tubebooks.org/books/zucconi_probes.pdf
On this forum, the discussion over recent years has tended to be concerned with achieving the high sensitivity, which people like Boonton and Marconi have done with RF Voltmeters, and what kind of "magic" diodes they are using!
B