A linear, low cost and versatile FM demodulator

The experimental behaviour of a low cost and versatile FM demodulator is described, designed for field applications where high linearity of the device is required in order to obtain a very low harmonic distortion of the signal to be measured. The circuit solutions which have been taken in order to reduce noise effects and to improve the dynamic range of the device are also discussed with reference to a vibration measuring system. A linearity uncertainty of less than +/-0.05% can be attained with reference to a frequency decade with input frequency to the demodulator in the range 50 kHz to 25 MHz.