Electromechanical filter element coupling - includes quarter wave quartz elements to reduce parasitic resonance outside passband by eight five db

摘要

Coupling arrangement for electro-mechanical elements that are employed in the longitudinal vibration mode. Coupling is via intermediate elements operating partly in the bending mode and minimises parasitic resonance outside the filter pass-band. The technique being esp. suitable for use in telephone exchange equipment. The coupling point can be attached at the node points of the most troublesome parasitic oscillations. The complete structure is mounted within two quarter wave quartz elements operating in the bending mode, the connection point being at the node point of the second mode oscillation. Attenuation outside the pass-band is greater than 85 db between 100 and 150 KHz apart from a very sharp band corresponding to the second operation mode of the resonators.