The Tachyon emitter is a device used by the Cardassians in 2378. They are satellite-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 emitters at Omega Draconis 3 and 5. (TNG video game: Bridge Commander)
To communicate with her group without tachyon interference, the Sovereign used short range point to point transmission with the battle group.