of shield 43 and enclosed coil windings 42 copper coated steel case 46 is electrically isolated from collar 14 a direct connection not illustrated between the ends of windings 42 and lead wires 36 extending from the transmitter circuitry is made in case 46 so that the lead lines continue a loop as the windings copper coated steel tube 47 extends from the end of passageway 34 to an opening in the top of case 46 to provide a conduit for lead wires 36 molded insulative material 23 fills recess 38 and encapsulates case 46 tube 47 shield 43 and coil 42 to provide a protective and electrically insulating cover for transmitter antenna 19 and to maintain the hydrostatic integrity of the drilling system tube 47 is in mechanical and electrical contact with the steel body of drill collar 14 at its upper end toward passageway 34 however tube 47 is isolated from electrical contact with case 46 by an electrically insulating annular spacer 48 thus transmitter lead lines 36 are electrostatically shielded by tube 47 and collar 14 which is electrically grounded at the transmitter circuitry thereby grounding the tube transmitter lead lines 36 may comprise a pair of coaxial cables with the center lead of the cables continuing as wire windings 42 of transmitter antenna coil 119 the shield lead not illustrated of each cable.