Threshold analysis and design of an FMFB demodulator through quasi-linear approximation

An FM feedback model which considers both the open-loop threshold and the feedback threshold is developed by means of a quasi-linear approximation. The model clarifies the relationships between the demodulation signal, feedback factor, and the IF filter bandwidth with respect to the threshold values, and provides a quantitative determination of whether the threshold is of the open-loop or feedback type. After establishing the theoretical design method, the method is applied to the case of Enloe's loop filter and the results compared with previous studies.