A rotary drill stem for a well including a central tubular element, and first and second connectors each including a threaded portion that can connect the element to another element. At least one of the connectors includes a chamber in communication with a pressure outside the chamber. The connector includes an annular signal transmission coupler. The annular coupler includes a ring having an annular coupling surface. The coupler includes an insulating support that leaves the annular coupling surface free. The coupler includes a piston surface axially opposite to the annular coupling surface. The annular coupler forms a piston.