Signal transmission system

Claim 1

IN A SYSTEM FOR DRILLING A BOREHOLE IN THE EARTH COMPRISING A DRILL STRING HAVING A FRILL BIT AT ONE END THEREOF, SAID DRILL STRING INCLUDING A PLURALITY OF SECTIONS OF DRILL PIPE JOINED TO ONE ANOTHER END TO END, LOGGING APPARATUS MOUNTED IN THE VICINITY OF SAID DRILL BIT, AND A SIGNAL TRANSMISSION CIRCUIT ELECTRICALLY COUPLING SAID LOGGING APPARATUS THROUGH SAID SECTIONS OF DRILL PIPE TO SURFACE ELECTRICAL EQUIPMENT AT THE END OF SAID DRILL STRING REMOTE FROM SAID DRILL BIT, EACH OF SAID SECTIONS OF DRILL PIPE HAVING A FIRST COIL DISPOSED AT ONE END THEREOF AND A SECOND COIL DISPOSED AT THE OTHER END THEREOF, THE FIRST COIL OF ONE PIPE SECTION AND THE SECOND COIL OF AN ADJACENT PIPE SECTION BEING INDUCTIVELY COUPLED TO ONE ANOTHER THEREBY COMPRISING A TRANSFORMER, CIRCUIT MEANS COUPLING SAID FIRST COIL TO SAID SECOND COIL WITHIN SAID SECTION OF DRILL TAPE, EACH OF SAID CIRCUIT MEANS INLCLUDING A SEMICONDUCTOR AMPLIFIER HAVING AN INPUT COUPLED TO ONE OF SAID COILS AND AN OUTPUT COUPLED TO THE OTHER OF SAID COILS, SAID FIRST COIL AND SAID SEMI-CONDUCTOR AMPLIFIER BEING IMBEDDED WITHIN A FIRST ANNULAR UNIT FORMED ESSENTIALLY OF EPOXY RESIN AND FITTED CLOSELY WITH SAID ONE END OF EACH OF SAID SECTIONS OF DRILL PIPE, AND SAID SECOND COIL BEING IMBEDDED WITHIN A SECOND ANNULAR UNIT FORMED ESSENTIALLY OF EPOXY RESIN AND FITTED CLOSELY WITHIN SAID OTHER END OF EACH OF SAID SECTIONS OF DRILL PIPE.