Minecraft wiki entry for Transmission, associated text: Vertical ARW is an analog repeater wire built on redstone ladders. It transmits signals only upward and in segments of 14 vertical blocks (use vertical ACW to close any gaps). Like horizontal ARW, the last dust of the previous segment must be the first dust of the next segment unless a short run of vertical ACW is used to connect the two segments.
Horizontal ARW built on a 3-wide staircase can be used to transmit analog redstone signal diagonally downward.