Sorry to be veering off from the original thread title but nice to hear that AM stereo still exists somewhere! I remember when it all began and almost every music programmed AM station boasted broadcasting in AM stereo. The problem was that nobody had an AM stereo radio. So at first AM stereo was just advertising hype!It just so happens that KGRN is broadcasting in C-QUAM AM stereo!
At some point I did get myself a used Plymouth Voyager van with AM stereo. I thought that it functioned and sounded great, they took care with those receivers to get the best sound possible from AM. When I got rid of the van I lamented that I didn't keep the radio, by that time AM stereo was disappearing from new vehicles.
Years later I picked up a used Sony AM stereo tuner from eBay. Sadly by that time almost all the AM stereo stations had disappeared. In Canada most AM station were "flipping" over to the FM band. Those stations remaining were mostly non music formats like talk, news and sports. The odd music station remained but without stereo.
I remember working late at night while listening to AM radio, one stereo music station was on the extended portion of the AM band. It was KCJJ Iowa City. My vehicle radio did not have AM stereo. The rest of the AM band was mostly filled with the same syndicated Coast to Coast AM show! No music to be had anywhere, not even on "The Big 89".
At home the Sony tuner that I had did not tune the "extended band", so no KCJJ there either! So you see the "stereo gods" must have been dead set against AM radio!
There is a direct parallel between AM stereo and Quad in how they were each developed, marketed and then abandoned.