Back around 2002, I saw AF in action on 91.5 WBEZ Chicago and 89.5 WBEW Chesterton. My Blaupunkt Alaska after-market receiver would automatically shift between 89.5 and 91.5 seamlessly, anytime the signal dropped below some threshold for a period of time. The only other place I saw it work was in east central Pennsylvania, on what I recall was a trio multicast (something like “96X”?) — that would have been useful for that Nine-FM trio of stations on 92.5, 92.7 and 99.9 way back then.

The WBEZ <=> WBEW configuration of AF was apparently cleared when WBEW broke away from 100% simulcast. I think it switched to Vocalo.