Calibration of downhole tools for drift

A logging tool 200 comprises a tool body 201, a transmitter antenna 204 associated with the tool body, transmitter electronics 227 coupled to the transmitter antenna, a first receiver antenna 206 associated with the tool body, first receiver electronics 214 coupled to the first receiver antenna, and a signal generator 228 coupled to the first receiver electronics which provides a calibration signal to the first receiver electronics. The signal generator is separate from the first transmitter electronics in order to minimize cross talk and interference. Also, the signal generator may provide the calibration signal at times when the transmitter is inactive, proximate measurements of a formation using the transmitter and receiver. Methods using the tool determine tool drift and correct formation measurements made using the tool.