There are a couple of stations on AM that literally have migrated to FM, but these are oddities, based upon co-channel skywave interference.
News-talker WJNT 1180 in Jackson, MS had the misfortune of being on the same frequency as Radio Marti, the Voice of America station beamed at Cuba. The Cubans, afraid of having their countrymen hear any information not orchestrated by party-controlled authorities, saw fit to jam Marti. This caused some problems for stations like WJNT.
There was a station in Nashville with a similar issue. 'Not sure if it's still on.
It is. 98.7 relaying the 1160 station. Like WJNT's, it only operates at night. Unlike WJNT's, to be honest it's no longer necessary - the powerful Cuban on 1160 has been gone for years, the strongest nighttime interference to this station comes from Chicago...
About a month ago, a petition was filed asking that the rules be amended to allow FM translators to relay AM stations. Translator coverage to be limited to the station's *daytime* contours. (in fact, in most cases the 250-watt translator power limit would be more restrictive than the daytime contours) I don't see much action on this and even if it were approved tomorrow it'd take years (if not decades!) for the Commission to act on any applications...
This is where we get into how an AM could migrate to FM. There are two systems that could be utilized. One is the HD2 channel of an existed HD operating FM.
From my experience with HD coverage I don't think this would be much improvement over the directional AM<grin>...
Wonder if any of the AM directionals are backfilling service area nulls with FM (FM can be directional)?
It's been done but not to my knowledge in Tennessee. WBT-FM in Charlotte, for example. KSL in Salt Lake recently launched a FM simulcast - though since KSL is non-directional fulltime I guess it isn't backfilling any nulls<grin>...
Most broadcasters would consider talk on FM as a waste because the higher fidelity is where you want your music formats.
Cumulus is using two FM frequencies for talk in Nashville. (99.7/100kw and 106.7/6kw equivalent) Citadel also has a FM sports station here. (104.5/58kw) Admittedly this is a rare case. Possibly spurred by the fact that there's only two AM stations with citywide nighttime coverage and one of them (WSM) is committed to a music format.
I just get back from trip to canada and this is underway there, am switching to fm.
For one thing, in Canada you must show that a new station has a realistic financial plan and that it won't split the advertising pie into enough pieces to damage existing stations. Merely being able to show it won't cause electrical interference isn't enough. As a result, many cities - even those of 200,000 population or more - have had available frequencies.
It also helped that the CKO national network of all-news stations went bust back in the early 90s. CKO had powerful FM stations in most major cities, and it took something like ten years for the government to reallocate their old frequencies. That's how the CBC could move their station in Toronto, the country's largest market, from 740AM to a 100kw FM signal on 99.1.
Finally, in Canada 3rd-adjacent frequencies can be used. (sometimes even 2nd-adjacent) 93.5 C3/94.1 C1; 100.7 C2/101.3 A; 104.5 C1/105.1 A; and 106.5 C3/107.1 C1 are all channel pairs in operation in Toronto. All of these stations are licensed to Toronto and most of them transmit from one of two buildings downtown - none of them are "rimshotters". This of course opens a lot more FM frequencies for potential AM conversions.
