I believe that along with the move to FM translators...
The FCC Order authorizing AM use of FM translators is very restrictive. The 60 dbu contour of the translator can't extend beyond 25 miles from the transmitter site
or beyond the AM's 2 mV contour, whichever is less. Plus, only presently licensed
translators are eligible. Assuming you can find an existing translator, that's a tough standard to meet. Especially for stations with a directional signal.
It's not uncommon for an AM station to have a deep null over an unpopulated area in order to maximize signal over the population; however, that null comes into play when determining whether you can use a translator since it sucks in the 2mV contour. Also, many AM's are located outside of the population center for real estate reasons, and that brings the 25 mile rule into play.
Some might say my post belongs on another discussion area. But I believe the translator order was offered, in part, as a result of the noise being introduced into the AM band due to IBOC. Frankly, the new translator rules just provide lip service to AM broadcasters.
I wonder if the stations that have been using translators under STA's will be required to adhere to the coverage/distance rules?