1. IN A SYSTEM FOR-DIFFUSING WITHIN A SHIELD STRUCTURE SIGNALS DERIVED FROM A DISTANT SOURCE WHICH RADIATES A MODULATED RADIO FREQUENCY CARRIER OF A GIVEN POLARIZATION, COMPRISING IN COMBINATION, A RECEIVING ANTENNA AT SAID STRUCTURE WHICH IS SELECTIVE TO SAID POLARIZATION, AT LEAST ONE INDUCTIVE FIELD-PRODUCING LOOP WITHIN SAID STRUCTURE WHICH IS ORIENTED TO SELECTIVELY PRODUCE AN INDUCTIVE FIELD WHICH IS OF A DIFFERENT POLARIZATION FROM SAID GIVEN POLARIZATION, A SOURCE OF SUB-RADIO-FREQUENCY CARRIER AT SAID STRUCTURE, MEANS CONNECTED TO SAID RECEIVING ANTENNA TO DETECT THE AUDIO FREQUENCY MODULATIONS IN THE SAID RADIO FREQUENCY CARRIER, MEANS TO MODULATE SAID SUB-