When the signal level of the spurious frequency is as high as that of the basic frequency, the oscillator will oscillate on the spurious frequency, which is called frequency hopping. The spurious frequency mode is often defined as the resistivity or the suppression ratio regarding the basic frequency. For most oscillators, frequency hopping can be prevented with the resistivity of the basic frequency from 1.5 to 2.0 or the suppression ratio from -6dB to -3dB.