How does the frequency of a radio signal affect the transmission range?
There is a complex answer to this, so lets put up the basics.
First, very low frequency (vlf) radio frequency (rf) energy can
"bend" and can travel around the world (literally) as well as
penetrate water to some degree. It can be received almost anywhere
on the globe. Is that enough range? U.S. Naval submarine
communications uses this phenomenon. Electromagnetic radiation
(emr) can also travel (propagate) via a "bounce" (can be reflected
and/or refracted) off the ionized upper atmosphere (depending on
frequency and angle of incidence), and, to a degree, bounce off
land and water. It can thereby "bounce" its way around the world.
There will be "dead spots" where the signal can't be "seen" by a
receiver - unlike a circumnavigating vlf wave. Both those
eventualities are power dependent, naturally. The bad news is that
if one wants to get a signal from point A to point B, there are
variables that will determine what "band" of transmission is best
suited to the task.