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Adjustment of operating characteristics of a telephone transmitter including an electret transducer
| Details |
Inventors: Greason, William D.; Gumb, Beverley W.; Busche, Alan C.; Foster, Eric;
Assignee: Northern Telecom Limited (Montreal, CA)
Primary Examiner: Schreyer; Stafford D.
Assistant Examiner:
Attorney, Agent or Firm: Jelly; Sidney T.
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. |
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DETAILED DESCRIPTION What is claimed is: 1.
A telephone transmitter including an electret transducer, comprising: a rear housing; a front cover attached to said rear housing and defining therewith a chamber; a printed circuit board mounted in said chamber; an electret transducer mounted on said printed circuit board, between said cover and said board; an aperture in said cover in alignment with said transducer; an electrical circuit on said printed circuit board, said electret transducer forming part of said circuit, said circuit including a first resistor of a predetermined value and a second resistor having a value selected after subjection of the electret transducer to a test signal, to bring the operating characteristics of the transmitter within predetermined limits.
2.
A transmitter as claimed in claim 1, said rear housing having an enclosed recess extending from an inner rear surface, said printed circuit board including electronic devices mounted on a rear surface of the printed circuit board and housed within said recess, said transducer mounted on a front surface of said printed circuit board.
3.
A transmitter as claimed in claim 2, said printed circuit board including a conductive pattern on said front surface, said devices connected to said pattern through said board, said resistor mounted on said front surface.
4.
A transmitter as claimed in claim 2 said rear housing having an open recess extending outward from said inner rear surface, a seal member positioned on said inner rear surface of the rear housing and extending around said open recess, said printed circuit board mounted on said seal to close said open recess from said chamber, and terminals positioned in said recess and connected to said electrical circuit.
5.
A transmitter as claimed in claim 4, including a cap member attached to an outer rear surface of said rear housing, said cap member including an aperture for access to said terminals.
6.
A transmitter as claimed in claim 5, including an extension on an outer rear surface of said cap member for alternatively receiving a modular jack or a strain relief member of a line cord
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Audio Signal Processing 
