The communication facility for system for low frequency communication by electromagnetic coupling, comprises at least one electromagnetic field transmitting andor receiving antenna in the form of a coil disposed on a substrate board serving as support, this board having a certain thickness. At least one carrier signal is generated in a beam spot and conveys communications data over at least one downlink 22\u201325 to the user terminals 15\u201318. An incision site is externally indicated by transilluminating the stomach and abdominal walls of the patient from within the stomach.