The paper presents the results of the investigation of the significance of the rejected part of the signal spectrum obtained from the magnetometer sensors. Sensors were installed in the prototype of the AIST small spacecraft. The measurement interval of the sensors significantly limited the spectral range of the measured signal from 0 to pi/6 rad/s. The problem of significance of the signal spectrum rejected part was solved by restoring an analog signal from its discrete readings using the Kotelnikov series. Then the spectrum of the restored signal was constructed. In addition, the interval of simulated measurements was significantly reduced. Significance estimation of the rejected part of the signal spectrum allows us to make a conclusion about the accuracy of the signal restoration from the raw data. The results of our work can be used in estimating various characteristics in cases of abnormal operation of measuring devices or spacecraft's degraded performance.