Northern Telecom Limited

Alan C Busche

Beverley W Gumb

Raymond C Freeman

Ronald G Wellard

Eric Foster

William D Greason

Karlo B Simonsen

Josef Talacek

A telephone handset with static discharge prevention has a dielectric membrane extending over the metal ferrule of the transmitter, the membrane spaced from the ferrule by an annular dielectric spacer. At the receiver, a metal shunt on the front of the receiver has a central aperture for acoustic access. An annular dielectric membrane is positioned in the aperture and a dielectric membrane extends over the aperture, dielectric member and shunt. The membrane has a small hole within the annular dielectric member. The dielectric membrane at the transmitter increases the breakdown voltage to a value which will avoid static discharge to the user. The dielectric membrane and dielectric spacer at the receiver forms a long and sinuous discharge path which raises the breakdown voltage to a value which also avoids static discharge to a user.

Telephone handset with static discharge prevention

A telephone handset for use in noisy locations has a noise cancelling electret transmitter which receives a normal acoustic input at the front end and a background noise acoustic input to the rear end. The input to the rear end is via a grill on the back side of the handset. A dielectric shield is positioned between the grill and the transmitter. A resistor is inserted in series with the transmitter to reduce the sensitivity and produce a lower than normal transmit level. Also, a filter is used to reduce the level of high frequency emphasis.

Telephone handset for use in noisy locations

A transmitter assembly for a telephone set uses a commercially available cartridge electric transmitter, by modifying the response curve. This is obtained by an adapter housing the transmitter with a first volume defined between the end of the transmitter and the end of the bore in which the transmitter fits. At the end of the bore there is an end wall with a hole therethrough, the hole covered with a layer of acoustic resistance material. A second volume is formed on the other side of the end wall, by a hollow formation on the wall of the transmitter housing of the handset. A slot is formed in the transmitter housing wall within the formation. The first volume provides damping, the hole and acoustic resistance material provides dB limitation at a particular frequency (1000 Hz) and the second volume and slot provide resonance at a second frequency (3000 Hz).

Transmitter assembly for a telephone handset

A dynamic telephone receiver which is capable of being used in association with hearing aids, has a flux coil positioned around the pole piece and magnet assembly. To minimize the strong magnetic leakage field radiated from the air gap, which can attract pins, paper clips and other ferrous metals a shunt can be provided at the face of the receiver. However, this also shunts or at least severely attenuates the AC field produced by the flux coil for inductive coupling to hearing aids. The shunt of this invention shunts only the leakage flux from the air gap with minimal effect on the AC field from the flux coil. The shunt is in the form of a cup, with a central aperture in the front face, surrounded by an annular ring which is connected to the outer wall of the cup by narrow arms. The inner circumference of the ring is formed down towards the magnet to form a lip which attracts stray flux from the air gap. The shunt also acts to hold the receiver assembly together.

Dynamic telephone receiver with magnetic shunt

A telephone transmitter including an electret transducer is connected to an electrical circuit mounted in the transmitter housing. A resistor which can be of varying value is also connected to the circuit, the value of the resistor being adjusted to bring the operating characteristics within predetermined values. This is done by applying a sound signal of known frequency to the transducer and measuring the output characteristics of the transducer. This enables the suitable value of resistor to be connected into the circuit. By this means variations arising from varying atmospheric conditions at assembly, and other causes, can be allowed for. The metallized strip or film of the electret is preferably mounted with a very slight Vee shaped formation to avoid tight manufacturing tolerances which occur with a straight, or flat, strip.

Adjustment of operating characteristics of a telephone transmitter

An acoustic mounting and coupler, for coupling a transducer of a handset to a transducer of a terminal or similar form of apparatus, such as a visual display terminal for deaf users, has a flexible tubular member attached to the housing of the terminal. At the upper end of the tubular member is a flexible disc having a plurality of readily deformable annular ribs. The tubular member provides for vertical movement and some tilting. The ribs give good air sealing between the handset and coupler. Ambient noise input is reduced and mechanical vibration to the transducer in the terminal is also reduced. Some degree of variation in geometry and dimensions of the handset can be accommodated. Some laxity in placement of the handset can also be accommodated.

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Dorchester, Canada

Alan C Busche