And I'll also add, that, if these horrible signals are more the norm than the exception for 50kw non-Ds, AM radio is even more screwed than I thought.
And this is a problem for many seemingly good AMs
Case in point: KFI in Los Angeles. The lowest frequency of the US clear channel stations, it lives in a desert area. Power line insulators get covered with dust and create noise everywhere. Add in noise from anything with a microchip or SCR as well as industrial machines and the MetroRail and every manner and kind of industrial machines and KFI has areas inside its 15 mV/m signal where the noise overcomes it. In the Glendale and Burbank areas I know of entire main streets where it is unlistenable, well within the inner suburbs.
Noise, bad receiver designs, the fact that nobody buys "a radio" anymore and the fact that about 85% of top 100 market AMs don't adequately cover the market and you have the reason for AM's decline. And, as more and more stations go to religion, ethnic or brokered models, there is less traffic on AM for the few remaining mass appeal stations.
Having programmed two of the better signal Los Angeles AM's in the somewhat recent past, I can say that even if given an AM today, I would probably refuse the offer as ultimately leading to failure if not disaster.