Why would a radio station be playing in another area?

Answer 1

The question is vague.

It's possible for a radio station to "tune" their broadcast area... obviously boosting their power will allow them to cover a larger area, but it's also possible to change the shape of the coverage area. Without going into the physics, with two aerials you can have either a very nearly circular area (most common) or a long skinny oval that reaches hundreds of miles in some directions and less than 20 in others.

In the US, the FCC limits both the power and broadcast area of radio stations. Stations that violate their FCC licenses are subject to penalties including fines and cancellation of their licenses.

However, a given company might own several stations in different locations, and broadcast essentially the same program on each of them (much like there's an NBC affiliate in most major cities, and they all show pretty much the same thing except during "local programming" times like the news and late at night).

There's also a phenomenon called "skip" that sometimes makes it possible to receive radio transmissions when you're well outside the nominal broadcast area. The FCC isn't particularly happy about this, but it's a natural effect and there's not a whole lot they can do about it. Stations don't rely on it or make a special effort for it, it just happens sometimes.

Finally, particularly in AM radio, there are a lot of what are called "daylight only" stations that operate only during the day (or, in most cases, during local weather emergencies regardless of the time of day) and a few "class A" or "clear channel" stations that are legally allowed by their license to substantially boost their signal at night (up to, generally, 50,000 watts). If you've noticed that you get one set of channels during the day and a different set, some of them from quite far away, at night, this is probably what's happening. When I was in high school near Kansas City, at nights it was easily possible to pick up WGN out of Chicago, about 400 miles away. There were also some old "border blaster" stations like XERF that operated just across the Mexican border and dwarfed even the US clear channel stations, operating at up to 250,000 watts of power, enough to take the signal all the way from Del Rio Texas up into Canada.

Since it's not clear exactly which of these you might be talking about, you'll have to choose one from the list that matches the observed behavior you've seen.