Demodulation filter for a signal modulated in binary frequency manner

摘要

The invention relates to a filter for demodulating signals modulated in frequency in binary manner by the switching of two frequencies Fa and Fb. On a piezoelectric crystal, is produced two surface wave filtering units, each comprising a transmitting transducer and a receiving transducer with interdigitated electrodes. The number of electrodes of the receiving transducer of the first unit is substantially equal to twice (2Fa-Fb)/2(Fb-Fa ) with a spacing of v/(2Fa-Fb), in which v is the propagation rate. In the case of the second unit, this number is approximately twice (2Fb-Fa)/2(Fb-Fa) with a spacing of v/(2Fb-Fa). The receiving transducers are preferably subdivided in each case into two juxtaposed transducers, whereof one is set back with respect to the other by a distance of approximately v/4Fa for the first unit and v/4Fb for the second.