Tachyon emitter

The Tachyon Emmiter is a device used by the Cardassians in 2378. They are sattelite-like devices which disrupt anything having to do with subspace including warp travel in the system and communication. The USS Sovereign and her battle group faced two tachyon emmiters at Omega Draconis 3 and 5. 

To communicate with her group without tachyon interference, the Soverign used short range point to point transmission with the battle group.