microbalance 60Qp194 oscillator piQund3 3dB fLO damped superheterodyne pendulums CKEG resonant LowFER anharmonic CFCH 6dB damping omegaQundr 11025 Hz fQunds oscillators 61672 Basilar DSFN 20kHz resonance gyrofrequency harmonics amplitude heterodyne oscillation cyclotron