Despite its rudimentary nature it does provide enough technical info to get a person well on their way to being a professional radio snoop. I have tried to keep the borax to a minimum. One of the all-round best Web sites for all things scanner and short wave is the Grove Enterprises site . It has catalogs, product reviews, articles, frequency lists, a great reference library, and links to other sites. Technically speaking, anything that uses an antenna can be listened in on.
Scanners gather signals from the radio spectrum devoted to short and medium range communications.
This equates to local, regional and statewide communications. Envision any governmental, private, or corporate entity that communicates via radio and you can listen in on them. Scanners cannot transmit. They can only receive. SWR listening is an area of devotion unto itself.