The very few AM signals I could get in my car, day or night, were either limited to a few miles.
Keep in mind that the allocations plan for radio was based on conditions in the early 30's.
- Cities were much smaller. Low power could cover most metros.
- Interference was much less. No computers, dimmers, etc.
- There were no car radios.
- Most listening was at night. The major network shows had big regional or clear channels and that was enough.
- The "Best" allocations ended up where the population was 80 years ago... Flint and not Phoenix, in other words.
There was once a wonderful AM station in Phoenix with a huge signal. But they moved it up the dial to a signal that doesn't even cover the metro area.
The calls moved, not the station. KOY switched to talk, and then 1230 took a standards format and they gave the KOY calls to it to change the image of 550 AM to "FYI." Dumb or not, the station did not move.
They put talk radio on the big signal but that hasn't been a good move so now are considering moving the talk signal to one of the best FM signals in the Valley. If they continue with this "strategy" they will have wrecked one of the best AM's and one of the best FM signals.
KOY/KFY as a talker moved to the top, and stayed there, beating KTAR which had been a leader for decades. Now that KTAR moved to FM, and is regularly beating KFYI in the sales demos, KFYI is obviously considering that it is time to move the product to FM as AM no longer has much appeal and the noise levels in the Phoenix metro are hard on that night signal, which is pretty limited.
Changes in listener preferences among those under 55 motivated changing the old MOR KOY 550 to talk. The same is happening with KFYI AM in considering going to FM.
The KOY calls may have been considered too identified with "old radio" and "old farts" to be kept on the talker... anyone's guess is good as to why they moved them.
And when all the audience is on smart phones and other such devices, they will shut down the AM and FM transmitters.