GB173495A - Improvements in or relating to hand combination telephonic apparatus - Google Patents

Abstract

173,495. Western Electric Co., Ltd., (Assignees of Curtis, A. S.). Dec. 24, 1920, [Convention date]. Telephone hand sets.-Relates to a microtelephone set in which highly efficient or sensitive transmitters and receivers are used, but nevertheless, howling is eliminated under the usual conditions cf operation. The Specification states that the howling which takes place is governed by the relation of the " vibration ratio " to the " transfer impedance " through the electrical circuit. The " vibration ratio " is defined as the ratio of the voltage generated in the transmitter, due to mechanical and acoustical vibrations communicated to ii by the receiver, to the receiver current causing such vibrations. The " transfer impedance " is the ratio of the voltage generated in the transmiiter to the current produced by it in the receiver. When the vibration ratio is equal to the transfer impedance, sustained howling will take place and a decrease of the vibration ratio will result in a corresponding decrease in the howling. Ic order to make the vibration ratio low, a cross-section having a large radius of gyration, or a material with a high ratio of modulus of elasticity to density, or a combination of the two, is employed. In order to prevent mechanical resonance in the walls of the instrument cases, they are made relatively thick and rigid. A handle of the I-beam type fulfils the requirements for an ideal hand set, but, owing to the difficulty in grasping and holding such a handle, the modification shown in Fig. 3 is adopted. The casings 2 and 3 are mounted on the handle 8 whose crosssection is reduced uniformly until the projections 9 and 10 are reached. The cross-section of the handle is shown in Fig. 4, in which the portions 4, 5 of the lower flange of the ideal I-section are positioned at 6, 7. Moulded insulating materials are employed for the handle and casings, and metallic conductors 11, 12 are embedded in the handle in order electrically to connect the circuits in the casings.