Someone mentioned AM Stereo above, I do know that Australia introduced this in 1985, using the Motorola C-QUAM system, however I'm not sure that it really took off that well, maybe Aussie240 can enlighten us?
I'm not even sure how AM Stereo would sound, given that all of the AM signals I've ever heard on the broadcast band have been mono-aural and it lacks any top-end, regardless of any signal conditioning you do to it (as in treble and midrange cut/boost).
AM stereo was indeed introduced in 1985 using the C-QUAM system. I built up a stereo receiver late 1985 using the Motorola IC and a valve front end. The sound quality was excellent, with much better channel separation than FM. By using a low selectivity front end you get the full transmitted bandwidth, which in Australia is usually not limited unlike in Europe.
It bothers me greatly that AM broadcasting has such a stigma when the transmitted signal can be very good if the station does the right thing. The problem is all these appalling solid state receivers with 3KHz bandwidth. Listen through a proper receiver and you won't need FM.
As to the eventual outcome of AM stereo here, it died away in the late 1990's. While there was a lot of promotion at the start, available receivers were few, although some car radios did have it. For talk stations, stereo is a wasted effort and there's no need for it. Given that Sydney had only four music stations on AM at the time there probably wasn't much incentive to buy a stereo receiver.
1053 2CA in Canberra is the only AM stereo station left that I'm aware of. Fortunately I can receive it at night and it plays decent music.
