By 1949 americans who lived within the range of a television stations in the country could watch tv, vastly changing the way that humans communicated with each other. what type of electromagnetic wave made tv technology possible?

Microwaves.

Explanation: First, we have a trivial answer, and that is the visible light, which is responsible to let the information on the tv to be seen by the user.

Now, TV technology was possible thanks to the microwaves, that are used because these can carry more energy than other types, and these microwaves needed a special technology because they couldn't be handled by the current technology at the time.