the coded envelope the operation of the communications coupler in its other mode of operation will now be described this mode of operation allows the downhole system to respond to surface system commands for transmitting data from the downhole system to the surface system and to down load data from a recorder that has recorded information about the formation drilled and or other drilling information in this mode of operation the communication is conducted according to a load modulated scheme the exciting coil driver 46 is continuously enabled so that coil 22 is continuously excited the serial coded data from the downhole system 14 the tool recorder are provided as the enabling control signal to the switch 62 a logic level of 0 causes switch 62 to assume its closed state while a logic level of 1 causes switch 62 to assume its open configuration when static switch 62 is in its closed configuration the effective power transmitted through coupling coils 22 and 30 is minimal since coil 30 is grounded through the switch 62 and sees no load thus the energy with the exception of a slight amount of heat dissipated energy remains stored in the coupling coils when the switch.