FreddyE1977 said:So the two most powerful FM stations in the country are both in Grand Rapids, Michigan?
And 3 of the top 6 are in the state of Michigan? I wonder why? Why did they initially think that
would be necessary? I have lived in Michigan and in most areas the ground is rather swampy,
leading to really great ground connectivity. I had much better luck with daytime DXing on both
AM and FM there than anyplace else I've been. I would think 320kW would be reserved for
places like Huntsville, Alabama where the ground conductivity is lousy.
You're thinking of AM groundwave Freddy. FM is mainly about line of sight, ground conductivity has nothing to do with it. If you have a transmitter sited atop a very tall tower (or a tall mountain or a very high building), it's signal will travel a long way; basically to the horizon (as seen from the tx location). Now, a lot of FMs are licensed to locations that are quite high above average terrain but most are not allotted that much wattage. The FCC figures that a tall tower + a certain number of watts = the same thing as a shorter tower + 50 kw. So you have stations in Chicago broadcasting from the top of Sears Tower, but with only 8 or 10 kw. They get out a long way, but aren't all that strong in most of their range (only right downtown do they overload smaller FM radios). There are even more extreme cases of stations broadcasting from very high mountains, but with something like 1000 watts. WZRT Rutland, VT comes to mind (Z 97.1). They have 1150 watts, but from almost 4,300' above sea level (2,600' above average terrain). Their signal can be heard far away (where the terrain cooperates) but is not strong anywhere. I used to get it in Concord, NH and, after a long 4 hour drive, could still hear it from W of Albany, NY. But, for most of that drive, it faded in and out far too much to listen to.
On the other hand, very powerful signals on shorter towers may not have quite as much range as an FM from a very high location; but they generally have a robust to overwhelming signal throughout most of that range. Basically, it goes away at the horizon - the shorter the stick, the closer in the horizon is. The grandfathered big signals often have both attributes, allowing them to go out a long way with a very usable signal that covers large areas (as opposed to a dx-grade signal which may go far, but isn't really listenable).
Why are so many in Michigan? I honestly have no idea. There's nothing inherently special about Michigan's geography that would make such stations more attractive to put there than anywhere else. Perhaps it's just a coincidence of history that you had stations vying to serve a wide area at just the right time. Also, many of Michigan's cities had a higher market ranking back in the 50s than they do now - and (in relative terms) it was also a more prosperous state. So, at that time, maybe you had more potential listeners for FM than in a less affluent area like, say, Alabama. Of course, nowadays, those circumstances have changed a great deal.