I communicate with a good number of LPFMs, although I've not talked to these guys. Because almost all LPFM stations are licensed to groups that want a radio station but do not have a background in radio or either only understand one aspect of running a radio station, many stations are funded mostly from their board member's wallets. They might have a small audience that likes them but not understand how to get the funding. Many scenarios are about like this: you have a few auto mechanics who decide they want a car dealership because they like working on cars. They can do a good job on the repairs but don't know all that is involved with running a car dealership. They're pretty good at maintaining and fixing cars and don't understand why their showroom and lot is not filled with customers because they're such good mechanics.
As for stations licensed by the FCC, an engineer described the FCC's 'separation' requirements. Stations, depending on their power and antenna height have a signal that reaches only so far before it fades away. If you imagine cars driving toward one another, the FCC has set minimal separation rules that prevent the approaching cars from having a head on collision. If the cars approaching each other need to safely stop before crashing head on, the distance they need to stop is based on how fast they are going. If you're going 10 miles per hour you don't need near the space as a car driving 70 miles per hour. Substitute miles per hour for watts and how high the antenna is over the terrain. In essence each station has a licensed wattage and height the FCC calculates so they make sure stations don't collide. It is much more complicated than this. Imagine a bunch of roads coming together at a traffic light. All of the cars going at different speeds must be able to stop safely at the light. If they apply the brakes and can all stop before reaching the intersection you have what we call a hole or an area no car needs in order to stop safely. It might be possible the area not required for any of the cars to stop safely can be occupied by a new car (or station) if it can stop without colliding with any of the other cars. You might ask what it the road is slick from rain or ice? When this happens we call it tropo, a temporary condition that is short-lived and usually not affecting all the stations at once. By this scenario you can see moving the position of the cars is based on all the cars on the road, not just one or two. Moving one or two cars only might cause a collision.
