Minecraft wiki entry for Redstone_Repeater, associated text: A repeater can be placed only on top of opaque blocks (dirt, stone, etc.), on top of upside-down slabs, upside-down stairs, furnaces, and glass. In Bedrock Edition, a repeater can also be placed on fences and stone walls. They can also be placed on some transparent blocks. See Opacity/Placement for more information. To place a repeater, use the Place Block control.