System for logging wells

Claim 1

IN A WELL TESTING SYSTEM, WHEREIN SIGNALS GENERATED BY A SIGNAL SOURCE IN A WELL ARE DETECTED BY A RECEIVER IN THE WELL AND ARE TRANSMITTED OVER A PAIR OF CONDUCTORS TO A SIGNAL-RESPONSIVE DEVICE AT THE SURFACE, THE IMPROVEMENT COMPRISING THE COMBINATION OF: A VOLTAGE SOURCE AT THE SURFACE; CONTROL MEANS LOCATED IN THE WELL ADJACENT SAID SIGNAL SOURCE FOR RENDERING SAID RECEIVER OPERATIVE TO TRANSMIT SAID SIGNALS OVER SAID CONDUCTORS AT A TIME THAT VARIES IN ACCORDANCE WITH THE VOLTAGE APPLIED TO SAID MEANS; MEANS FOR CONNECTING SAID PAIR OF CONDUCTORS AS A CONDUCTOR OF A PHANTOM CIRCUIT BETWEEN SAID VOLTAGE SOURCE AND SAID CONTROL MEANS;