In this paper, eddy current signals from various anomalous defects in the steam generator tube are numerically predicted and their signal slope characteristics are investigated. The signal variations due to increased frequencies are also observed. Based on the accumulated knowledge, the analysis of compound signal is attempted which includes the effect of support plate. Both differential and absolute bobbin probe signals are analyzed. For the signal prediction, axisymmetric finite element modeling is used and this leads us to the utilization of slope angle analysis of the signal. Results show that differential signals are useful for locating the position of defect under the support plate, while absolute signals are easy to presume and interpret even though the effect of support plate is mixed. Combined use of these two types of signals will help us accomplish a more reliable inspection.