Patent GB-1075556-A (GB)
Title: Improvements in or relating to carrier terminal apparatus
IPC: H03H9/05
Filed: 1965-08-23
Abstract: 1,075,556. Carrier telephony systems; electromechanical filters. SIEMENS A.G. Aug. 23, 1965 [Aug. 24, 1964], No. 36019/65. Headings H3U and H4R. Carrier terminal apparatus in which a number of speech channels are modulated to the frequency band 60-108 kc/s., either directly or by the formation of sub groups in the band 12 to 24 kc/s. which are in turn modulated to the 60-108 kc/s.band, has electromechanical filters to separate the desired side band of the modulation process, the filters having resonant elements constituted by elongated members in which bending oscillations are set up. Five embodiments of mechanical filters are described. Fig. 6 shows one embodiment of a mechanical filter in whichelongated members 21, 22 and 23 are supported by wires 25, 26, attached at nodal points of the members 21- 23, in the frame 1. Electrostrictive transducer 5 is attached to the member 21 so that it may be excited in bending oscillation in the direction indicated by the arrows 12. The oscillation is communicated from one member to the next by wire 30 which is attached to studs, Fig. 5 (not shown), at antinodal points on the surface of the members, the wire being prestressed so that longitudinal vibrations are transmitted by the wire without the wire having to transmit compressive forces. In an alternative embodiment, Fig. 4 (not shown), only two resonant members are used and the coupling wire extends past the members and is secured to resilient brackets 13, 14, mounted on the, baseplate, which prestress the wire. Fig. 7 shows an embodiment in which a bending oscillation is excited in a member in the direction shown by arrows I by a transducer (not shown). A flat 52 couples the oscillation. I to produce a further oscillation in the direction shown by arrows II, both these oscillations are coupled to member 51- by coupling members 60, 61 to produce oscillations in the directions III and IV which are intercoupled by chamfer 52 and an electrostrictive transducer is attached to one face of the member 51 to derive an output signal. The bending members may be directly excited by the arrangement as shown in Fig. 10 in which electrostrictive material is arranged between sections of the member, the material being polarized so that the appropriate feed voltage applied between the faces of the material, or between an electrode, e.g. 131, in the centre, of the block of material and the parts 120, 121 and 122 of the bending member causes, e.g., the electrostrictive material in 123, 124 to expand and that in 125, 126 to contract to initiate bending of the member, the oscillations in, the bar being detected by the other electrostrictive transducers 127 to 130. Fig. 11 shows an embodiment in which bending oscillations are initiated directly in one plane, e.g. 1, in a member 231, by electrostrictive material 213, 214, 215 and 216, the oscillations are coupled to the plane II by the flats 222 and oscillations in both the planes are coupled to the other member by a coupling bar 212, the second member oscillating by bending in the planes III and IV which oscillations are coupled by the flats 222 while an output from the member is obtained via the electrostrictive elements 217 to 220 according to the oscillations in plane IV. An equivalent circuit is given for this filter, Fig. 12 (not shown).