Instructions
Select the Forge editor while on the Halo main screen. Press "up" on the D-pad, located on the controller, to enter editor mode.
Press "X" to bring up the in-game editing menu. Select the "gadgets" option to bring up an additional editing menu.
Scroll down to the option labeled "teleporters" and select it. Once selected, choose any of the three teleporters: Receiver Node, Sender Node or Two-Way Node. A silver, circular object will appear on your screen -- is the teleporter node. Your reticule will turn from blue to green to indicate that you are holding the node.
Press "X" while holding the "node," and a new menu will appear giving you the ability to change the size of the top, bottom and radius of the teleporter.
Select the "radius" option and move your left joystick to the left to decrease the size of the teleporter or right to increase it by increments of 0.1. The radius starts at 0.0 and goes to 99.9, with 0.0 being the smallest and 99.9 being the largest. Choose the largest size available to create a big teleporter.