In the last Hub World, Foxington, there are 5 blueish-greenish radios casually hanging around. You need to interact with all 5 radios by hitting them with
. Foxington is a small area so they are quite easy to find, but just in case you can find a video below. Credit of the video goes to Brandon Brickhouse.
Timestamps for the video, as I know we are all very impatient: