S4:Ep.4: Jack has concluded that Techno communications must be run on a network of one or more cell towers. So all they'd need to do is knock those out to bring all communications down. To prove his theory he goes hunting with Ebony, using a detector gismo.
"Whoo! I mean this things pumping out energy. I wonder where they're getting their power from. That's it - that's the cell tower! Come on, let's get a closer look..."
No Jack, that's a satellite dish, not a cell tower.