GB1334650A - Circuit arrangements for the frequency conversion of electrical information signals - Google Patents

Abstract

1334650 Transistor frequency-changing circuits; multiplex systems SIEMENS AG 13 March 1972 [12 March 1971] 11556/72 Headings H3U H3T and H4R A circuit for the frequency conversion of electrical information signals comprises an electromechanical filter, the input and output resonators of which are each provided with an electrostrictive transducer, followed by a symmetrical modulator, wherein the electrostrictive transducer on the output side of the electromechanical filter is supplemented by an inductor which forms a parallel resonance circuit; wherein the inductor and a symmetrical winding are windings of a transformer, and wherein the modulator is connected to the symmetrical winding. The electromechanical filter comprises a number of round steel rods 1, Fig. 5, each having a flat on one side, by which it is attached at its centre to a longitudinal vibratory member 3. Each rod is supported by means of a corresponding support 4 from a base-plate 5; the end rods are attached to the member 3 at a point spaced 90 degrees from their flats, the flats being the points of attachment of electrostrictive elements 2, 2<SP>1</SP> which are electrically parallel-resonant with inductors 12, 12<SP>1</SP> respectively. The oscillatory excitation of the resonators 1 is such that they execute bending mode oscillations in the direction 6; i.e. parallel to the base-plate 5. The filter is surrounded by a housing 7; between the filter body and this is a layer 8 of sound absorbing material, e.g. synthetic polyester fleece. The modulator may comprise a pair of transistors 17, 17<SP>1</SP>, Fig. 7, driven in push-pull from electromechanical filter 9 via transformer 13<SP>1</SP>, the filter being terminated by means of resistors R1, R2, to the join 30 of which a carrier frequency is supplied. In a second embodiment a double push-pull modulator 15<SP>1</SP>, Fig. 8, is employed, in this case as a demodulator.