We have the answer to one of the great puzzles in anime. Marc Hairston talked with Yoshitoshi ABe recently and asked what radio station the shopkeeper was listening to in the second episode of Haibane Renmei.
He said it was local and the antenna was inside the wall. Apparently the wall blocks any radio signals from outside Glie.
There’s also a possibility of the story continuing with an older Rakka, and ABe is working on a novel.