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Tone signal detector
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Patent number 4,231,018
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Issue date Oct 28, 1980
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Nippon Electric Co., Ltd.
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Masayuki Imigawa
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H04 - ELECTRIC COMMUNICATION TECHNIQUE
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3866124
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Patent number 3,866,124
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Issue date Feb 11, 1975
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H04 - ELECTRIC COMMUNICATION TECHNIQUE
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3859475
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Patent number 3,859,475
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Issue date Jan 7, 1975
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H04 - ELECTRIC COMMUNICATION TECHNIQUE
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3833861
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Patent number 3,833,861
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Issue date Sep 3, 1974
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H04 - ELECTRIC COMMUNICATION TECHNIQUE
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3823375
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Patent number 3,823,375
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Issue date Jul 9, 1974
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G08 - SIGNALLING
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3798545
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Patent number 3,798,545
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Issue date Mar 19, 1974
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H04 - ELECTRIC COMMUNICATION TECHNIQUE
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3783384
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Patent number 3,783,384
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Issue date Jan 1, 1974
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H04 - ELECTRIC COMMUNICATION TECHNIQUE
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3781890
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Patent number 3,781,890
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Issue date Dec 25, 1973
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H04 - ELECTRIC COMMUNICATION TECHNIQUE
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3731200
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Patent number 3,731,200
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Issue date May 1, 1973
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H04 - ELECTRIC COMMUNICATION TECHNIQUE
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3715726
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Patent number 3,715,726
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Issue date Feb 6, 1973
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G08 - SIGNALLING
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3714375
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Patent number 3,714,375
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Issue date Jan 30, 1973
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H04 - ELECTRIC COMMUNICATION TECHNIQUE
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3702440
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Patent number 3,702,440
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Issue date Nov 7, 1972
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H04 - ELECTRIC COMMUNICATION TECHNIQUE
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3691464
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Patent number 3,691,464
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Issue date Sep 12, 1972
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H04 - ELECTRIC COMMUNICATION TECHNIQUE
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3651413
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Patent number 3,651,413
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Issue date Mar 21, 1972
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H04 - ELECTRIC COMMUNICATION TECHNIQUE
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3619784
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Patent number 3,619,784
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Issue date Nov 9, 1971
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H04 - ELECTRIC COMMUNICATION TECHNIQUE
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3613004
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Patent number 3,613,004
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Issue date Oct 12, 1971
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H04 - ELECTRIC COMMUNICATION TECHNIQUE