Frequency Transmitter
The Frequency Transmitter (Brought to you by IndustrialCraft 2 Classic, or IC2C), can be used to link Teleporters between each other and Teleporter Hubs.
Teleporter between Teleporter/Teleporter Hub Connections
To use the Frequency Transmitter to link two teleporters between eachother, shift-right-click one of the Teleporters. A text message should appear saying "Frequency Transmitter linked to Teleporter". When you hover your mouse over the Frequency Transmitter, the coordinates of the Teleporter should appear. Go over to your second Teleporter, and shift-right-click that teleporter. Another message should appear in chat saying "Teleportation link established". Your teleporters are now linked! The same process is used for the Teleporter Hub.
To clear the coordinates of a Frequency Transmitter, right-clicking in the air will do the trick!