Piezoelectric ceramic I.F. filters in transistor radio receivers

An important application of polarized ferroelectric ceramics like barium titanate and lead zirconate titanate (PZT) is in their use as i.f. filters in transistor radio receivers. These filters employ thin circular discs with ring-and-dot electrode configurations vibrating in the first overtone of radial mode. Experimental investigations have been conducted on the circular PZT discs to assess theirsuitability as i.f. filters in transistor radio receivers. From the measurements made on the electrical characteristics of the filter such as input and output impedances, selectivity and insertion loss, an i.f. strip consisting of a conventional i.f. transformer followed by two ceramic filters has been designed. This i.f. strip is used in a transistor receiver and its overall performance characteristics such as sensitivity, selectivity and fidelity have been determined. The measured values are selectivity: greater than 24 db and 43 db at 10 kcs and 20 kcs respectively; sensitivity: 140 ¿V at 1 Mc and 14 ¿V at 10 Mcs; and fidelity: ¿3 db points at 90 and 1700 cps. The subjective performance of the receiver is quite satisfactory.