Electrical audio signal processing systems and devices – Circuitry combined with specific type microphone or loudspeaker
Reexamination Certificate
1999-05-10
2001-04-24
Isen, Forester W (Department: 2747)
Electrical audio signal processing systems and devices
Circuitry combined with specific type microphone or loudspeaker
C381S114000
Reexamination Certificate
active
06222928
ABSTRACT:
ORIGIN OF THE INVENTION
The invention described herein was made in the performance of official duties by employees of the Department of the Navy and may be manufactured, used, licensed by or for the Government for any governmental purpose without payment of any royalties thereon.
1. Field of the Invention
The invention relates generally to microphone-to-radio connections, and more particularly to an impedance matcher that allows a microphone (e.g., a powered piezoelectric microphone) to automatically be impedance matched to almost any two-way radio.
2. Background of the Invention
Military and civilian two-way radios are typically designed for use with a specific microphone. In each case, the microphone's impedance value is matched to an input impedance of its corresponding radio. Typical input impedances for HF, VHF, or SATCOM radios fall between the broad range of 5-2000 ohms. Thus, interchanging microphones (necessitated by failure, breakage, lost, etc.) between radios often results in an impedance mismatch between microphone and radio. The impedance mismatch can cause a significant reduction in the microphone's apparent performance.
As mentioned above, microphones are subject to failure and breakage. This is especially true in rugged environments. Accordingly, the U.S. Navy has developed a waterproof, powered, piezoelectric microphone that operates extremely well in rugged and high-noise environments. However, as also mentioned above, the number of different types of radios used by the military means that impedance matching of the microphone to the different radios is a time consuming and costly endeavor. Eliminating risk of a mismatch during operations and minimizing inventory requirements are two major benefits.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an impedance matcher that would allow a microphone to be automatically impedance-matched to a variety of radios.
Another object of the present intention is to provide an impedance matcher for use with powered microphones.
Still another object of the present invention is to provide an impedance matcher that is small and economical to build.
Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings.
In accordance with the present invention, an impedance matching circuit couples a microphone's output to a radio's microphone input. The input impedance for the microphone input is within a prescribed range. A tap circuit is coupled to the microphone's output for extracting an audio signal therefrom. The audio signal has an AC component and a DC component. An amplifier circuit having DC blocking circuitry is coupled to the tap circuit for passing the AC component and blocking the DC component. An audio transformer is also provided with its primary and secondary windings defining a turns ratio of approximately 1:1. Further, the primary winding has a characteristic DC resistance that is less than approximately 100 ohms and the secondary winding has an impedance that is within the prescribed range of the input impedance for the microphone input. A driver circuit is coupled between the amplifier circuit and audio transformer for continuously driving the audio transformer with the AC component.
REFERENCES:
patent: 4535205 (1985-08-01), Ravinet et al.
patent: 5036536 (1991-07-01), Hanon et al.
patent: 5185789 (1993-02-01), Hanon et al.
Downs, Jr. Edward F.
Venturella Kevin M.
Gilbert Harvey A.
Isen Forester W
Peck Donald G.
Pendleton Brian Tyrone
The United States of America as represented by the Secretary of
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